Research ArticleInfluence of Heat Treatment on Biocorrosion andHemocompatibility of Biodegradable Mg-35Zn-3Ca Alloy

Jeong-Hui Ji1 Il-Song Park2 Yu-Kyoung Kim1 Sook-Jeong Lee3

Tae-Sung Bae1 and Min-Ho Lee1

1Department of Dental Biomaterials and Institute of Biodegradable Material Institute of Oral Bioscience and BK21 Plus ProjectSchool of Dentistry Chonbuk National University Jeonju 561-756 Republic of Korea2Division of Advanced Materials Engineering and Institute of Biodegradable Material Chonbuk National UniversityJeonju 561-756 Republic of Korea3Department of NewDrugDiscovery andDevelopment ChungnamNational University Yuseong Daejeon 305-764 Republic of Korea

Correspondence should be addressed to Min-Ho Lee lmhjbnuackr

Received 19 December 2014 Accepted 21 January 2015

Academic Editor Jinghuai Zhang

Copyright copy 2015 Jeong-Hui Ji et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

Mg-35Zn-3Ca (wt) alloy containing nontoxic and biocompatible Zn and Ca as alloying elements was prepared and subjectedto heat treatment and artificial aging for different duration of time to reduce its rate of degradation Solution heat treatment wasperformed at 310∘Cwhile artificial aging was performed at 170∘C for 0 25 50 75 and 100 h and they were designated as AT0 AT1AT2 AT3 and AT4 respectively The finest and most homogenous reticulum was observed on the surface of the AT2 group Theresult of immersion test in Hankrsquos balanced salt solution (HBSS) showed that the corrosion rate of the AT2 group was 232mg(cm2day) which was significantly lower as compared to other groups (119875 lt 005) The hemolysis value was le5 in all groups indicatingno toxicity during short-term blood reaction

1 Introduction

Implants are widely used for the replacement and treatmentof abnormally functioning bone tissues due to diseases orinjuries Among the various types of implants that are cur-rently being used ceramic- or polymer-based implants haveunsatisfactorymechanical properties while metal-based onesare considered suitable for load bearing implant applicationsdue to their superior mechanical strength and durabilityStainless steel titanium and its alloys and Co-Cr alloysare some of the commonly used materials for fabricatingmetallic implants However these implants pose a high risk ofrelease of toxic heavymetals or generating finemetallic debrisparticles induced by corrosion or wear or by tribocorrosionwhich could cause inflammation in the surrounding tissues[1ndash5] In addition the difference in Youngrsquos modulus betweenthese implants and bone tissues could cause stress-shieldingeffect resulting in stress concentration on the contact planebetween the natural bone and the implant This leads to

a reduction of the stimuli required for the new bone growththereby lowering the success rate of the implant [6]

Mg and its alloys possess a low density high mechanicalstrength and fracture toughness In addition they are bio-compatible and biodegradable [7] Youngrsquos modulus of Mgand its alloys are closer to the natural bone than stainlesssteels titanium and its alloys and Co-Cr alloys Mg isthe fourth abundant ion in the human body and it is anessential component for human metabolism The daily Mgintake of a normal adult is 300ndash400mg and the excess Mgions are excreted via urine [8ndash12] Mg which is a naturalcomponent of bone tissues helps bone growth and increasesbone strength [13] These attributes form the basis that Mgand its alloys can be explored towards the developmentof degradable biomaterials For load-bearing applicationbiodegradable implants must be retained in the body for atleast 12ndash18 weeks a time period which is usually requiredfor natural growth of bone tissues after treatment or surgerywhile maintaining sufficient mechanical strength [14 15]

Hindawi Publishing CorporationAdvances in Materials Science and EngineeringVolume 2015 Article ID 318696 10 pageshttpdxdoiorg1011552015318696

2 Advances in Materials Science and Engineering

Unfortunately Mg and its alloys undergo rapid corrosion inchloride containing solutions such as body fluid resultingin the generation of a huge volume of hydrogen gas withalkalinization of the medium [16] The hydrogen gas thusgenerated could cavern under the subcutaneous tissue andunder a worst scenario the hydrogen gas bubbles couldblock the blood flow causing death of the patient [8] Thusstudies on purification alloying and surface coating havebeen explored to resolve the rapid biodegradation of Mg andits alloys

Among the various alloys evaluated for biodegradableimplant applications Al-Zn based Mg alloys such as AZ91and AZ31 as well as rare earth based Mg alloys such asLAE442 and WE43 have received considerable attentionHowever whenAl-Zn basedMg alloys are used as degradableimplants the accumulation of aluminum in the body couldcause neurogenic disorders such as Alzheimerrsquos diseaseparticularly dementia and senile dementia [17] In case ofrare earth based Mg alloys cerium praseodymium andyttrium show hepatotoxicity and hence they are consideredinappropriate for use as degradable implants [18] Calciumis an important component of the natural bone As a bio-material it has advantages for being essential in cellularsignal transduction and for having density similar to thatof the bone [19] When Ca is added to Mg alloy Mg

2Ca

with high melting point is formed and a protective oxidelayer is also formed to improve corrosion resistance therebyincreasing hardness and creep resistance [20] Zinc is one ofthe typical inorganic matters that constitutes somatic cellsand regulates physiological functions Its deficiency in thebody could cause various anomalies such as low birth weightduring delivery and growth and developmental problems IfZn and Ca are added to Mg a stable intermetallic compoundCa2Mg6Zn3is formed that could help in age-hardening [21]

and in increasing the tensile strength and ductility of the alloy[22]

In the present study to reduce the biodegradation rate ofMg and to improve its biocompatibility in the body a ternaryMg alloy using Zn and Ca as nontoxic and biocompatiblealloying elements was preparedThe as-prepared ternaryMg-Zn-Ca alloy was subjected to heat treatment followed byartificial aging for different duration of time to alter themicrostructure so as to improve the corrosion resistancebiocompatibility and hemocompatibility

2 Materials and Methods

21 Materials Mg-35Zn-3Ca (wt) alloys were preparedusing magnesium (9993 Sincere East Co China) zinc(9990 Sincere East Co China) and calcium (9950 Jun-sei Chemical Co Ltd Japan) The experimental alloys weremelted in vacuum arc remelting furnace (Ace Vacuum CoKorea) equipped with water-cooling Cu hearth Vacuum arcremelting was performed in presence of argon gas (9999)at 50 times 10minus5 Torr under a current and voltage of 300A and12V respectively Melting was performed five or more timesto prevent segregation and remelting 10 more times whileflipping over to obtain homogeneity in Mg-Ca master alloy

Mg-35Zn-3Ca alloy was manufactured using a vacuuminduction melting furnace (Ace Vacuum Co Korea) Zincwas loaded on the bottom of alumina crucible and the Mg-Ca master alloy and Mg element were cross-loaded on top ofthe loaded zincThe alumina crucible was preheated for 200 sfollowed bymelting and agitation for 10min by increasing thepower in an interval of 200 sThe solutionwas poured into thealumina cast to produce Mg-35Zn-3Ca alloy

For the microstructure observation and assessment ofthe corrosion resistance of heat treated cast alloy a 164mmdiameter Mg stick was sliced into 2mm thickness before use

22 Methods

221 Heat Treatment and Artificial Aging In order to deter-mine the suitable temperature for solution heat treatment theMg-35Zn-3Ca alloy specimens were analyzed using Differen-tial Scanning Calorimetry (DSC) (TA Q20 TA InstrumentsLtd USA) Both the Mg-Zn-Ca alloy specimen and refer-ence materials underwent heatingcooling at a constant rateunder the same condition The temperature difference thatoccurs between the Mg-Zn-Ca alloy specimen and referencematerial either by exothermic or endothermic reactions wasadjusted by supplying the required amount of energy and thetransformation temperature was determined by measuringthe amount of the supplied energy

For solution heat treatment the Mg-Zn-Ca alloy spec-imens were placed inside an electric arc furnace (AjeonIndustrial Co Ltd Korea) and the temperature of the furnacewas raised to 310∘C at a heating rate of 10∘Cmin and thesamples were soaked for 48 h followed by quenching in dis-tilledwater at room temperature Some of the specimensweresubjected to artificial aging following solution heat treatmentFor artificial aging the specimens were placed in an electricarc furnace and the temperature of the furnace was raisedto 170∘C at a heating rate of 10∘Cmin Then the specimenswere soaked for various time intervals from 25 to 100 hSpecimens which were subjected to only heat treatment at310∘C were designated as AT0 whereas those subjected toan additional artificial aging for 25 50 75 and 100 h weredesignated as AT1 AT2 AT3 and AT4 respectively Thedetails of the experimental conditions employed for heattreatment and artificial aging are compiled in Table 1

222 Surface Examination and Analysis The heat treatedand artificially aged Mg alloy specimens were sequentiallypolished by SiC coated abrasive papers (grit size 800 to1600) followed by polishing using 03 120583m Al

2O3pow-

der and ultrasonic cleaning in distilled water for 5minThe polished specimens were carefully etched in 2 Nitaletchant (ethanol HNO

3= 98mL 2mL) for 5 s with a peri-

odic assessment of surface microstructure for any sign ofacidic corrosion The microstructure of the Mg-Zn-Ca alloyspecimens was examined by scanning electron microscopy(SEM) (JSM-5900 JEOL Japan) (low magnification images)and by field emission scanning electron microscopy (FE-SEM) (SUPRA 40VP Carl Zeiss Co Ltd Germany) (highmagnification images) In addition the concentration of the

Advances in Materials Science and Engineering 3

Table 1 Details of the heat treatment parameters of the Mg-35Za-3Ca alloy

Type of treatment Group designation and treatment conditionsAT0 AT1 AT2 AT3 AT4

Solution treatment 310∘C 48 h 310∘C 48 h 310∘C 48 h 310∘C 48 h 310∘C 48 hAging treatment Untreated 170∘C 25 h 170∘C 50 h 170∘C 75 h 170∘C 10 h

elements present in the alloy and their distribution weredetermined using energy dispersive X-ray analysis (EDX)(Oxford England)

223 Potentiodynamic Polarization Test Potentiodynamicpolarization test was used to assess the electrochemicalcorrosion behavior of Mg-Zn-Ca alloy specimens An elec-trochemical cell consisting of AgAgCl KCl (satrsquod) as thereference electrode a platinum plate as the counter electrodeand Mg-Zn-Ca alloy specimens subjected to heat treatmentand artificial aging for different duration of time as theworking electrode connected to a potentiostatgalvanostat(273A EGampG PARC USA) was used for the study Theexperiments were performed with exposing the area 1 cm2in 150mL of Hanks solution whose chemical composition ispresented in Table 2 The potentiodynamic polarization testwas performed in the potential range minus05 V to +05V ata scan rate of 3mVs at room temperature The corrosionpotential (119864corr) and current density (119894corr) were calculatedfrom the measured polarization curves using Tafel extrapo-lation method followed by assessment of extent of corrosionthe specimens

224 Immersion Test The initial pH of the HBSS wasadjusted to 72 with the incremental additions of eitherNaOH (01molL) or HCl (01molL) using a pHmeter (HD-PHP Davis Co Ltd USA) The Mg-Zn-Ca alloy specimenssubjected to heat treatment and artificial aging for differentduration of time were immersed in 45mL of HBSS andincubated at 37∘C for 72 hThe change in pH of the HBSS wasmeasured as a function of immersion time

225 Measurement of Corrosion Rate The Mg-Zn-Ca alloyspecimens subjected to heat treatment and artificial agingfor different duration of time were immersed in 45mL ofHBSS and incubated at 37∘C for 5 days The HBSS wasreplaced every 24 h to suppress the change in concentrationof the solution during the test After 5 days of immersionthe Mg alloy specimens were rinsed in deionized waterand ultrasonically cleaned using isopropanol for 5min toremove the corrosion products attached to the specimenThe specimens were washed with distilled water and thendried To examine weight changes in the specimen caused bycorrosion the specimen weight was measured before and 5days after depositionThe corrosion rate was calculated usingthe following equation [23]

119862119877=119882

119860 times 119905 (1)

Table 2 Chemical composition of Hankrsquos balanced salt solution(HBSS)

Constituents Quantity (gL)Potassium phosphate monobasic [anhydrous] 006Sodium phosphate dibasic [anhydrous] 004788Potassium chloride 04Sodium chloride 80Phenol red Na 0011D-Glucose 10

where 119862119877is corrosion rate 119882 is weight loss 119860 is surface

area of the specimen exposed to the etching reagent and 119905is exposure time

226 Hemolysis Assessment The test solution used forhemolysis assessment was blood samples collected from thecoronary artery of rats which were treated with heparinand diluted with saline solution in a 4 5 ratio (vol)Specimens having a dimensions of 164mm diameter and2mm thickness from each experimental group were treatedwith 10mLof saline solution for 30min and the elutewas usedas the experimental group 10mL saline solution containing01 wt of Na

2CO3and 10mL saline solution were used

as the positive and negative control groups respectivelyEach 10mL solution of each group (experimental group andthe positive and negative control group) was mixed with02mL of the prepared test solution and incubated at 37∘Cfor 60min Subsequently each mixture was centrifuged at680G for 3min and 200120583L of the supernatant liquid wascollected Then absorbance was measured at 540 nm using amedical enzyme analyzer (Emax Molecular Devices USA)The measured absorbance was used to assess the percentagehemolysis by the following equation [24]

hemolysis () =OD (test) minusOD (negative)

OD (positive) minusOD (negative)times 100

(2)

3 Results

The SEM image of the microstructure of the as-cast Mg-35Zn-3Ca alloy etched using Nital for 5 s and its chemicalcomposition analyzed by EDX analysis are shown in Figure 1The microstructure of the alloy is homogeneous and revealsno casting defects The chemical composition of the alloyindicates the presence of Mg (6382wt) Zn (3263wt)

4 Advances in Materials Science and Engineering

(a)

100 200 300 400 500 600 700 800

Ca

Zn

MgLSecs 42

Zn

00

31

124

62

93

155

900

KCnt

Energy (keV)

(b)

Figure 1 SEM micrograph of as-cast Mg-35Zn-3Ca (a) and EDX spectrum results (b)

Table 3 Elemental composition of Mg-35Zn-3Ca alloy assessed byenergy dispersive X-ray analysis

Atomic Weight Ca 276 355Zn 1554 3263Mg Balance Balance

and Ca (355 wt) as the major elements (Table 3) suggest-ing that the alloy conforms to the chemical compositionrequirements of Mg-35Zn-3Ca alloy

The DSC trace of the as-cast Mg-35Zn-3Ca alloy speci-men is shown in Figure 2 The liquidus and solidus temper-atures are 36184∘C and 34011∘C respectively Based on thisresult the suitable temperature for solution heat treatment isset as 310∘C which is slightly lower than the solidus tempera-ture of the alloy Accordingly the as-cast Mg-35Zn-3Ca alloyis homogenized at 310∘C for 48 h and quenched in deionizedwater at room temperature to prevent any microsegregationand residual stress during precipitation (designated as AT0)Some of the specimens were subjected to artificial aging heattreatment at 170∘C for 25 50 75 and 100 h and designatedas AT1 AT2 AT3 and AT4 respectively

The SEM images of the surface microstructure of theheat-treated (AT0) and artificially aged (AT1 AT2 AT3 andAT4) Mg-35Zn-3Ca alloy specimens etched in Nital for 5 sare shown in Figure 3 Among all the specimens the AT2group exhibits the finest and most homogenous distributionof 120572 and 120573 phases It is also evident from Figure 3 thatwith increase in aging time the size of 120572 phase is increasedwith the disappearance of the boundary of 120573 phase resultingin a change in microstructure from a homogeneous to aninhomogeneous state The X-ray elemental mapping of MgZn and Ca along with the secondary electron image ofthe Mg-35Zn-3Ca alloy is shown in Figure 4 It is evidentthat the darker regions of the microstructure are mostlythe 120572-Mg matrix whereas the lighter regions are mainly the

240 260 280 300 320 340 360 380 400 420

00

02

34011

34556 36184

34973

Temperature (∘C)

minus02

minus04

minus06

minus08

Hea

t flow

(cal

(g s

))

Figure 2 DSC thermogram (heating curve) of as-cast Mg-35Zn-3Ca alloy

120573-phase precipitate which are relatively lower in Mg andlargely consist of zinc and calcium

The potentiodynamic polarization curves of heat-treated(AT0) and artificially aged (AT1 AT2 AT3 and AT4) Mg-35Zn-3Ca alloy specimens in HBSS are shown in Figure 5The119864corr and 119894corr values of all the specimens calculated usingTafel extrapolation method are compiled in Table 4 There isnot much variation in the 119864corr of all the specimens testedand all of them lie in the range of minus120 to minus129V versusAgAgClKCl (satrsquod) The 119894corr values of the specimens thatare heat-treated and artificially aged for different duration oftime (AT1 to AT4) are relatively higher than those subjectedonly for heat treatment (AT0) Among the heat treated andartificially aged samples (AT1 to AT4) specimens of the AT2group exhibit a lower 119894corr Based on the 119894corr values thecorrosion resistance of the Mg-35Zn-3Ca alloys specimenssubjected to only heat treatment (AT0) and heat treatmentfollowed by artificial aging for different duration of time (AT1to AT4) can be ranked as follows AT0 gt AT2 gt AT3 gt AT4 gtAT1

Advances in Materials Science and Engineering 5

(a) (b) (c)

(d) (e) (f)

(g) (h) (i)

(j) (k) (l)

(m) (n) (o)

Figure 3 Surface morphology of various heat treated Mg-35Zn-3Ca alloys (a) AT0 (times2000) (b) AT0 (times5000) (c) AT0 (times10000) (d) AT1(times2000) (e) AT1 (times5000) (f) AT1 (times10000) (g) AT2 (times2000) (h) AT2 (times5000) (i) AT2 (times10000) (j) AT3 (times2000) (k) AT3 (times5000) (l) AT3(times10000) (m) AT4 (times2000) (n) AT4 (times5000) and (o) AT4 (times10000)

6 Advances in Materials Science and Engineering

Table 4 Electrochemical corrosion parameters of Mg-35Zn-3Ca alloy in HBSS derived from the potentiodynamic polarization test usingTafel extrapolation method

GroupAT0 AT1 AT2 AT3 AT4

119864corr (V vs AgAgClKCl (satrsquod)) minus129 minus123 minus123 minus120 minus123119894corr (120583Acm

2) 1011 5091 3641 3751 4908

CaZn

Mg

Figure 4 Analysis of elemental composition on the surface by EDX mapping of Mg-35Zn-3Ca alloy

Pote

ntia

l (V

ver

sus A

gClK

Cl)

AT0AT1AT2

AT3AT4

minus11

minus12

minus13

minus141E minus 8 1E minus 7 1E minus 6 1E minus 5 1E minus 4 1E minus 3

Current density (Acm2)

Figure 5 Potentiodynamic polarization curve obtained in HBSSvarious heat treated Mg-35Zn-3Ca alloys

The change in pH of the HBSS in which the Mg-35Zn-3Ca alloys subjected to only heat treatment (AT0) and heattreatment followed by artificial aging for different durations(AT1 to AT4) are immersed measured for a duration of 72 his shown in Figure 6 In general all the specimens exhibita rapid increase in pH during the first 6 h beyond whichthe extent of increase in pH is decreased Beyond 48 h ofimmersion the pH of HBSS reached a stable value for all thespecimens studiedDuring the first 6 h of immersion theMg-35Zn-3Ca alloy specimens subjected to heat treatment alone(AT0) showed a rapid increase in pHwhen compared to thosesubjected to heat treatment followed by artificial aging fordifferent duration of time (AT1 to AT4) Among the AT1 toAT4 group specimens of the AT2 group showed a relativelyless increase in pH suggesting the lower extent of dissolutionof the Mg alloy

The corrosion rate of the Mg-35Zn-3Ca alloy specimenssubjected to only heat treatment (AT0) and heat treatmentfollowed by artificial aging for different duration of time (AT1to AT4) calculated using the loss in weight after immersionin HBSS at 37∘C for 5 days is shown in Figure 7 It is evident

Advances in Materials Science and Engineering 7

0 12 24 36 48 60 72

pH

Ageing time (hour)

7

8

9

10

11

AT0AT1AT2

AT3AT4

Figure 6 pH value as a function of immersion time

AT0 AT1 AT2 AT3 AT40

1

2

3

4

232

308308

373

Sample code

392

Cor

rosio

n ra

te (m

g(c

m2

day)

)

Figure 7 Corrosion rates of different heat treated Mg-35Zn-3Caalloys after immersion in HBSS for 5 days

that specimens subjected to heat treatment alone (AT0) showa higher corrosion rate (392mg(cm2 day)) when comparedto those subjected to heat treatment followed by artificialaging for different durations (AT1 to AT4) (ranging from232 to 373mg(cm2 day)) Among the AT1 to AT4 groupspecimens of the AT2 group showed a lower corrosion rate of232mg(cm2 day) which is significantly lower than those ofother groups (119875 lt 005)

In vitro hemolysis test is a well-known method to assessthe biotoxicity in a short duration of time The hemolysisability of Mg-35Zn-3Ca alloy specimens subjected to onlyheat treatment (AT0) and heat treatment followed by arti-ficial aging for different duration of time (AT1 to AT4) ismeasured using the positive (10mL saline solution containing01 wt of Na

2CO3) and negative (10mL saline solution)

as controls The measured optical density values and the

Table 5 Absorbance value measured at 540 nm and percentage ofhemolysis of Mg-35Zn-3Ca alloy subjected to heat treatment andartificial aging for different duration of time

Sample code OD at 540 nm Hemolysis ()AT0 0051 plusmn 0002 0515 plusmn 0375AT1 0050 plusmn 0002 0371 plusmn 0204AT2 0049 plusmn 0001 0147 plusmn 0104AT3 0050 plusmn 0001 0299 plusmn 0275AT4 0051 plusmn 0002 0521 plusmn 0272Negative 0049 plusmn 0001 0Positive 0495 plusmn 0013 100

hemolysis are compiled in Table 5 The variation in the hemolysis of all the samples tested alongwith the negative andpositive controls is plotted in Figure 8 for a better comparisonand to understand the statistical difference among themIt is evident from Table 5 and Figure 8 that among all thespecimens tested those belonging to the AT2 group showedthe lowest value of hemolysis (0147) However whencompared to other groups the difference in hemolysis isstatistically insignificant (119875 gt 005)

4 Discussion

Mg undergoes rapid corrosion in electrolytes containingchlorides such as body fluid Hence it will be difficult touse Mg for implant applications When Mg is exposed to airthe oxide layer formed on its surface offers only a partialprotection In aqueous solution the formation of porousMg(OH)

2layer could not offer much protection (equation

(3)) In presence of chloride ions it gets dissolved as MgCl2

while the aggressive nature of the medium causes severecorrosion of theMg (equations (4) and (5)) [25]The reactionsequences ofMg in aqueousmedium in the absence (equation(3)) and presence (equations (4) and (5)) of chloride ions canbe represented as follows [8]

Mg (solid) + 2H2O 997888rarr Mg (OH)

2+H2(gas) (3)

Mg (solid) + 2Clminus (aqueous) 997888rarr MgCl2

(4)

Mg (OH)2(solid) + 2Clminus 997888rarr MgCl

2 (5)

The corrosion resistance of Mg could be improvedthrough alloying formation of composites surface treat-ment and heat treatment [25ndash31] However the alloyingelements the second phase materials used to prepare thecomposites and the surface treated layer should not beharmful to the body when used as a biomaterial Someof the commonly used Mg-based alloys contain aluminumthat is harmful to the nervous system and osteoblasts whilethe RE-based Mg alloys could cause blood toxicity [1718] In the present study Mg-35Zn-3Ca alloy is preparedby adding zinc and calcium as alloying elements both ofwhich are nontoxic Alloying magnesium with zinc enablesprecipitation hardening while alloying with calcium couldhelp in grain refinement The microstructure and corrosion

8 Advances in Materials Science and Engineering

AT0 AT1 AT2 AT3 AT4 Negative Positive

0

1

2

90

100

05150371

01470299

0521

100

Hem

olys

is (

)

Sample code

0

Figure 8 Hemolysis percentage of various heat treated Mg-35Zn-3Ca alloys

resistance of the Mg-35Zn-3Ca alloy are evaluated aftersubjecting them to only heat treatment (AT0) and heattreatment and artificial aging for different duration of time(AT1 to AT4)

The microstructural examination after solution heattreatment and artificial aging heat treatment performed overa specific period of time showed that the 120572 and 120573 phaseswere finest and most homogenous in the AT2 group whichunderwent an artificial aging heat treatment at 170∘C for5 h Moreover the grain boundary was broken and 120573 phasewas inhomogeneous in the AT3 group which underwentartificial aging heat treatment for 75 h Results also showedthat the size of crystal grain became larger and the continuityof the crystal margin has disappeared in the AT4 groupwhich underwent artificial aging heat treatment for 10 h(Figure 3) Solution heat treatment is a process to preparethe supersaturated solid solution of unstable state materialsare generally softened by solution heat treatment Previousstudies have reported that artificial aging heat treatmentfollowing solution heat treatment of Mg alloy improvedstrength by refinement of the precipitate [29] Meanwhile itwas reported that heat treatment changed the microstruc-ture of alloy thereby affecting the corrosion behavior[32 33]

In this study potentiodynamic polarization studieschange in pH of HBSS and loss in weight after immersionin HBSS were used to assess the corrosion resistance of theMg-35Zn-3Ca alloy both in as-prepared and heat-treatedconditions The results of the potentiodynamic polarizationtest conducted to assess electrochemical corrosion behaviorshowed the lowest corrosion current density of 1011120583Acm2for the AT0 group which underwent only the solutionheat treatment Among the groups that underwent artificialaging following solution heat treatment the lowest corro-sion current density of 3641 120583Acm2 is observed for theAT2 group The corrosion current density which is closelyassociated with corrosion rate is an intersection point atwhich the negative Tafel slope is extrapolated to corrosionpotential by the Tafel extrapolation method [34] This resultshowed that corrosion resistance of the Mg-35Zn-3Ca alloy

is much improved for the group that underwent solution heattreatment alone than in groups that underwent artificial agingheat treatment following solution heat treatment Whenimmersed in HBSS Mg undergoes anodic dissolution withthe release of H

2gas and generation of OHminus ions resulting

in an increase in pH of the medium [35] These reactionsequences can be represented as follows [36]

Anodic reaction Mg 997888rarr Mg2+ + 2e (6)

Cathodic reaction 2H2O + 2e 997888rarr H

2+ 2OHminus (7)

Formation of corrosion product

Mg2+ + 2OHminus 997888rarr Mg (OH)2

(8)

Thus the rate of corrosion of MgMg alloys could beestimated from the change in pH of the corrosive medium(HBSS in this study) as a function of time The change inpH of the HBSS measured as a function of time (Figure 6)showed that it is slowest for specimens in the T2 group whencompared to other groups This inference indicates that thecorrosion resistance is increased as the microstructure ofthe surface gets finer and denser The loss in weight of thespecimens measured after 5 days of immersion in HBSS is232mg(cm2 day) for the AT2 group which is significantlylower than that of the other groups (119875 lt 005) The lossin weight is 392mg(cm2 day) for the AT0 group whichis the highest among all the specimens tested Howeverthe difference between the specimens is insignificant whencomparedwith the specimens in other groups except with theAT2 group (119875 gt 005) Hence it is clear that the specimens ofthe AT2 group have offered an excellent corrosion resistancewhich is consistent with the results of change in pHHoweverthe results are inconsistent with those of the potentiodynamicpolarization test The fineness and homogeneity of the 120573phase largely determine the corrosion behavior which isreflected in the pH variation and weight loss These resultssupported that corrosion behavior of magnesium alloyswith multiphase structure is changed according to corro-sion potential difference distribution and volume fractionbetween micr-constituent phases [16 37 38] Since thesemeasurements are made for a long term the ability of the120573 phase to act as a physical barrier for corrosion becomeseffective [33 39] However during the electrochemical studysince the test is performed over a short duration the effect isnot reflected [29]

The hemolysis test which is conducted to assess thetoxicity to the body uses the principle that red blood cellsare divided or necrotized when the hemoglobin is destroyedThe concentration of free hemoglobin is proportional to thenumber of the injured RBC and the volume of the fluid [2440] The results of hemolysis test showed that the percentageof hemolysis (0147) in AT2 group is the lowest among allthe samples tested and when compared with other groups nostatistical significance difference could be observed (Figure 8Table 5) (119875 gt 005) In general if the hemolysis value is 5or less then it is considered as nonhemolytic according to

Advances in Materials Science and Engineering 9

ISO 10993-42002 [41] Accordingly the composition of Mg-35Zn-3Ca has low hemolysis and analogies good biocompat-ibility In other words homogenization and aging process ofthe Mg-35Zn-3Ca alloy can improve the physical propertiesand corrosion resistance of the material and it does not havea significant effect on the hemolytic toxicity

5 Conclusions

The preparation of Mg-35Zn-3Ca alloy containing zinc andcalcium rather than aluminum or RE elements as nontoxicand biocompatible alloying elements followed by heat treat-ment and artificial aging of the alloy to control its rate ofdegradation is reported The study leads to the followingconclusions

(1) DSC studies showed that the liquidus and solidustemperatures of the Mg-35Zn-3Ca alloy were36184∘C and 34011∘C respectively

(2) The microstructural features of the Mg-35Zn-3Caalloy indicate the presence of 120572-Mg matrix and 120573phase after heat treatment and artificial aging forvarious duration of time Among them the AT2group (heat treatment at 170∘C for 5 h followed byartificial aging at 310∘C for 48 h) exhibits the finest andmost homogenous distribution of 120572 and 120573 phases

(3) Potentiodynamic polarization studies of the Mg-35Zn-3Ca alloy specimens indicate that the 119894corr valuesof specimens that are heat-treated and artificiallyaged for different duration of time (AT1 to AT4) arerelatively higher than those subjected only to heattreatment (AT0) Among heat-treated and artificiallyaged samples (AT1 to AT4) specimens of the AT2group exhibit a lower 119894corr Based on the 119894corr valuesthe specimens can be ranked as follows AT0 gtAT2 gtAT3 gt AT4 gt AT1

(4) The change in pH of theHBSSmeasured for 72 h indi-cates that all the specimens exhibit a rapid increase inpH during the first 6 h during which the Mg-35Zn-3Ca alloy specimens subjected to heat treatment alone(AT0) showed a rapid increase in pH Beyond 48 hof immersion the pH of HBSS reached a stable valuefor all the specimens studied Among the AT1 toAT4 groups specimens of the AT2 group showed arelatively less increase in pH suggesting the lowerextent of dissolution of the Mg alloy

(5) Mg-35Zn-3Ca alloy specimens subjected to heattreatment alone (AT0) showed a corrosion rate of392mg(cm2 day) than those subjected to heat treat-ment followed by artificial aging for different dura-tions (AT1 to AT4) which ranges between 232 and373mg(cm2 day) Among the AT1 to AT4 groupsspecimens of theAT2 group showed a lower corrosionrate of 232mg(cm2 day) which is significantly lowerthan those of other groups (119875 lt 005)

(6) In vitro hemolysis test showed the lowest hemolysispercentage value of 0147 for the AT2 group but

the differences were statistically insignificant whencompared with that of other groups (119875 lt 005) Thehemolysis was 5 or less for all groups which indi-cates no significant hemoglobin destruction whichsuggests that Mg-35Zn-3Ca alloy has no cytotoxicity

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Authorsrsquo Contribution

Il-Song Park contributed to this work and is considered asjoint first author

Acknowledgments

This work was supported by the National Research Founda-tion of Korea (NRF) Grant funded by the Korea government(MSIP) (no 2011-0028709 and no 2014R1A4A1005309) andRegional Strategic Industry project (2013-R0002274)

References

[1] D A Puleo and W W Huh ldquoAcute toxicity of metal ions incultures of osteogenic cells derived from bone marrow stromalcellsrdquo Journal of Applied Biomaterials vol 6 no 2 pp 109ndash1161995

[2] J J Jacobs J L Gilbert and R M Urban ldquoCurrent conceptsreview Corrosion of metal orthopaedic implantsrdquo The Journalof Bone amp Joint Surgery vol 80 pp 268ndash282 1998

[3] C Lhotka T Szekeres I Steffan K Zhuber and K ZweymullerldquoFour-year study of cobalt and chromium blood levels inpatients managed with two different metal-on-metal total hipreplacementsrdquo Journal of Orthopaedic Research vol 21 no 2pp 189ndash195 2003

[4] J J Jacobs A K Skipor L M Patterson et al ldquoMetal releasein patients who have had a primary total hip arthroplasty Aprospective controlled longitudinal studyrdquoThe Journal of Boneand Joint SurgerymdashAmerican Volume vol 80 no 10 pp 1447ndash1458 1998

[5] J J Jacobs N J Hallab A K Skipor and R M UrbanldquoMetal degradation products a cause for concern in metal-metal bearingsrdquo Clinical Orthopaedics and Related Researchno 417 pp 139ndash147 2003

[6] J Nagels M Stokdijk and P M Rozing ldquoStress shielding andbone resorption in shoulder arthroplastyrdquo Journal of Shoulderand Elbow Surgery vol 12 no 1 pp 35ndash39 2003

[7] H G Seiler H Sigel and A Sigel Handbook on Toxicity ofInorganic Compounds 1988

[8] M P Staiger A M Pietak J Huadmai and G Dias ldquoMag-nesium and its alloys as orthopedic biomaterials a reviewrdquoBiomaterials vol 27 no 9 pp 1728ndash1734 2006

[9] E P DeGarmo J T Black and R A Kohser DeGarmorsquosMaterials and Processes in Manufacturing John Wiley amp Sons2011

[10] L J Gibson and M F Ashby Cellular Solids Structure andProperties Cambridge University Press 1999

10 Advances in Materials Science and Engineering

[11] J-W Choi Y-M Kong H-E Kim and I-S Lee ldquoReinforce-ment of hydroxyapatite bioceramic by addition of Ni

3

Al andAl2

O3

rdquo Journal of the American Ceramic Society vol 81 no 7pp 1743ndash1748 1998

[12] T Thamaraiselvi and S Rajeswari ldquoBiological evaluation ofbioceramic materialsmdasha reviewrdquo Trends in Biomaterials andArtificial Organs vol 18 no 1 pp 9ndash17 2004

[13] H Zreiqat C R Howlett A Zannettino et al ldquoMechanismsof magnesium-stimulated adhesion of osteoblastic cells tocommonly used orthopaedic implantsrdquo Journal of BiomedicalMaterials Research vol 62 no 2 pp 175ndash184 2002

[14] F Witte V Kaese H Haferkamp et al ldquoIn vivo corrosionof four magnesium alloys and the associated bone responserdquoBiomaterials vol 26 no 17 pp 3557ndash3563 2005

[15] C EWenMMabuchi Y Yamada K Shimojima Y Chino andT Asahina ldquoProcessing of biocompatible porous Ti and MgrdquoScripta Materialia vol 45 no 10 pp 1147ndash1153 2001

[16] G Song ldquoRecent progress in corrosion and protection ofmagnesium alloysrdquo Advanced Engineering Materials vol 7 no7 pp 563ndash586 2005

[17] S S A El-Rahman ldquoNeuropathology of aluminum toxicityin rats (glutamate and GABA impairment)rdquo PharmacologicalResearch vol 47 no 3 pp 189ndash194 2003

[18] Y Nakamura Y Tsumura Y Tonogai T Shibata and Y ItoldquoDifferences in behavior among the chlorides of seven rare earthelements administered intravenously to ratsrdquo Toxicological Sci-ences vol 37 no 2 pp 106ndash116 1997

[19] J Z Ilich and J E Kerstetter ldquoNutrition in bone health revisiteda story beyond calciumrdquo Journal of the American College ofNutrition vol 19 no 6 pp 715ndash737 2000

[20] J C Oh T Ohkubo T Mukai and K Hono ldquoTEM and 3DAPcharacterization of an age-hardened Mg-Ca-Zn alloyrdquo ScriptaMaterialia vol 53 no 6 pp 675ndash679 2005

[21] G Levi S Avraham A Zilberov and M Bamberger ldquoSolidifi-cation solution treatment and age hardening of a Mg-16 wtCa-32 wt Zn alloyrdquo Acta Materialia vol 54 no 2 pp 523ndash530 2006

[22] T Miyazaki J Kaneko and M Sugamata ldquoStructures andproperties of rapidly solidified Mg-Ca based alloysrdquo MaterialsScience and Engineering A vol 181-182 pp 1410ndash1414 1994

[23] C Liu Y Xin G Tang and P K Chu ldquoInfluence of heattreatment on degradation behavior of bio-degradable die-castAZ63 magnesium alloy in simulated body fluidrdquo MaterialsScience and Engineering A vol 456 no 1-2 pp 350ndash357 2007

[24] X Gu Y Zheng Y Cheng S Zhong and T Xi ldquoIn vitrocorrosion and biocompatibility of binary magnesium alloysrdquoBiomaterials vol 30 no 4 pp 484ndash498 2009

[25] B A Shaw Corrosion Resistance of Magnesium Alloys vol 13ASM handbook 2003

[26] V Kaesel P T Tai F Bach H Haferkamp F Witte and HWindhagen ldquoApproach to control the corrosion of magnesiumby alloyingrdquo inMagnesium Proceedings of the 6th InternationalConference Magnesium Alloys and Their Applications pp 534ndash539 Wiley Online Library 2004

[27] J E Gray and B Luan ldquoProtective coatings on magnesium andits alloysmdasha critical reviewrdquo Journal of Alloys and Compoundsvol 336 no 1-2 pp 88ndash113 2002

[28] M-C Zhao M Liu G Song and A Atrens ldquoInfluence of the120573-phase morphology on the corrosion of the Mg alloy AZ91rdquoCorrosion Science vol 50 no 7 pp 1939ndash1953 2008

[29] N N Aung andW Zhou ldquoEffect of heat treatment on corrosionand electrochemical behaviour of AZ91D magnesium alloyrdquoJournal of Applied Electrochemistry vol 32 no 12 pp 1397ndash14012002

[30] G Song A L Bowles and D H StJohn ldquoCorrosion resistanceof aged die cast magnesium alloy AZ91DrdquoMaterials Science andEngineering A vol 366 no 1 pp 74ndash86 2004

[31] M Jonsson D Persson and R Gubner ldquoThe initial steps ofatmospheric corrosion on magnesium alloy AZ91Drdquo Journal ofthe Electrochemical Society vol 154 no 11 pp C684ndashC691 2007

[32] T Beldjoudi C Fiaud and L Robbiola ldquoInfluence of homog-enization and artificial aging heat treatments on corrosionbehavior of Mg-Al alloysrdquo Corrosion vol 49 no 9 pp 738ndash7451993

[33] O Lunder J E Lein T K Aune and K Nisancioglu ldquoRole ofMg17Al12 phase in the corrosion of Mg alloy AZ91rdquo Corrosionvol 45 no 9 pp 741ndash748 1989

[34] D L Piron The Electrochemistry of Corrosion University ofHouston Houston Tex USA 1991

[35] G Song A Atrens D Stjohn J Nairn and Y Li ldquoThe electro-chemical corrosion of pure magnesium in 1 N NaClrdquo CorrosionScience vol 39 no 5 pp 855ndash875 1997

[36] Z Li X Gu S Lou and Y Zheng ldquoThe development of binaryMg-Ca alloys for use as biodegradable materials within bonerdquoBiomaterials vol 29 no 10 pp 1329ndash1344 2008

[37] A E Coy F Viejo P Skeldon and G E Thompson ldquoSus-ceptibility of rare-earth-magnesium alloys to micro-galvaniccorrosionrdquo Corrosion Science vol 52 no 12 pp 3896ndash39062010

[38] G Song and A Atrens ldquoUnderstanding magnesiumcorrosionmdasha framework for improved alloy performancerdquoAdvanced Engineering Materials vol 5 no 12 pp 837ndash8582003

[39] A F Crawley and K S Milliken ldquoPrecipitate morphology andorientation relationships in an agedMg-9Al-1 Zn-03Mnalloyrdquo Acta Metallurgica vol 22 no 5 pp 557ndash562 1974

[40] S O Sowemimo-Coker ldquoRed blood cell hemolysis duringprocessingrdquoTransfusionMedicine Reviews vol 16 no 1 pp 46ndash60 2002

[41] ISO ldquoBiological evaluation of medical devicesmdashPart 4 selec-tion of tests for interactions with bloodrdquo Tech Rep ISO 10993-4 2002

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CeramicsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CompositesJournal of

NanoparticlesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Biomaterials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MetallurgyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

MaterialsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nano

materials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofNanomaterials

2 Advances in Materials Science and Engineering

Unfortunately Mg and its alloys undergo rapid corrosion inchloride containing solutions such as body fluid resultingin the generation of a huge volume of hydrogen gas withalkalinization of the medium [16] The hydrogen gas thusgenerated could cavern under the subcutaneous tissue andunder a worst scenario the hydrogen gas bubbles couldblock the blood flow causing death of the patient [8] Thusstudies on purification alloying and surface coating havebeen explored to resolve the rapid biodegradation of Mg andits alloys

Among the various alloys evaluated for biodegradableimplant applications Al-Zn based Mg alloys such as AZ91and AZ31 as well as rare earth based Mg alloys such asLAE442 and WE43 have received considerable attentionHowever whenAl-Zn basedMg alloys are used as degradableimplants the accumulation of aluminum in the body couldcause neurogenic disorders such as Alzheimerrsquos diseaseparticularly dementia and senile dementia [17] In case ofrare earth based Mg alloys cerium praseodymium andyttrium show hepatotoxicity and hence they are consideredinappropriate for use as degradable implants [18] Calciumis an important component of the natural bone As a bio-material it has advantages for being essential in cellularsignal transduction and for having density similar to thatof the bone [19] When Ca is added to Mg alloy Mg

2Ca

with high melting point is formed and a protective oxidelayer is also formed to improve corrosion resistance therebyincreasing hardness and creep resistance [20] Zinc is one ofthe typical inorganic matters that constitutes somatic cellsand regulates physiological functions Its deficiency in thebody could cause various anomalies such as low birth weightduring delivery and growth and developmental problems IfZn and Ca are added to Mg a stable intermetallic compoundCa2Mg6Zn3is formed that could help in age-hardening [21]

and in increasing the tensile strength and ductility of the alloy[22]

In the present study to reduce the biodegradation rate ofMg and to improve its biocompatibility in the body a ternaryMg alloy using Zn and Ca as nontoxic and biocompatiblealloying elements was preparedThe as-prepared ternaryMg-Zn-Ca alloy was subjected to heat treatment followed byartificial aging for different duration of time to alter themicrostructure so as to improve the corrosion resistancebiocompatibility and hemocompatibility

2 Materials and Methods

21 Materials Mg-35Zn-3Ca (wt) alloys were preparedusing magnesium (9993 Sincere East Co China) zinc(9990 Sincere East Co China) and calcium (9950 Jun-sei Chemical Co Ltd Japan) The experimental alloys weremelted in vacuum arc remelting furnace (Ace Vacuum CoKorea) equipped with water-cooling Cu hearth Vacuum arcremelting was performed in presence of argon gas (9999)at 50 times 10minus5 Torr under a current and voltage of 300A and12V respectively Melting was performed five or more timesto prevent segregation and remelting 10 more times whileflipping over to obtain homogeneity in Mg-Ca master alloy

Mg-35Zn-3Ca alloy was manufactured using a vacuuminduction melting furnace (Ace Vacuum Co Korea) Zincwas loaded on the bottom of alumina crucible and the Mg-Ca master alloy and Mg element were cross-loaded on top ofthe loaded zincThe alumina crucible was preheated for 200 sfollowed bymelting and agitation for 10min by increasing thepower in an interval of 200 sThe solutionwas poured into thealumina cast to produce Mg-35Zn-3Ca alloy

For the microstructure observation and assessment ofthe corrosion resistance of heat treated cast alloy a 164mmdiameter Mg stick was sliced into 2mm thickness before use

22 Methods

221 Heat Treatment and Artificial Aging In order to deter-mine the suitable temperature for solution heat treatment theMg-35Zn-3Ca alloy specimens were analyzed using Differen-tial Scanning Calorimetry (DSC) (TA Q20 TA InstrumentsLtd USA) Both the Mg-Zn-Ca alloy specimen and refer-ence materials underwent heatingcooling at a constant rateunder the same condition The temperature difference thatoccurs between the Mg-Zn-Ca alloy specimen and referencematerial either by exothermic or endothermic reactions wasadjusted by supplying the required amount of energy and thetransformation temperature was determined by measuringthe amount of the supplied energy

For solution heat treatment the Mg-Zn-Ca alloy spec-imens were placed inside an electric arc furnace (AjeonIndustrial Co Ltd Korea) and the temperature of the furnacewas raised to 310∘C at a heating rate of 10∘Cmin and thesamples were soaked for 48 h followed by quenching in dis-tilledwater at room temperature Some of the specimensweresubjected to artificial aging following solution heat treatmentFor artificial aging the specimens were placed in an electricarc furnace and the temperature of the furnace was raisedto 170∘C at a heating rate of 10∘Cmin Then the specimenswere soaked for various time intervals from 25 to 100 hSpecimens which were subjected to only heat treatment at310∘C were designated as AT0 whereas those subjected toan additional artificial aging for 25 50 75 and 100 h weredesignated as AT1 AT2 AT3 and AT4 respectively Thedetails of the experimental conditions employed for heattreatment and artificial aging are compiled in Table 1

222 Surface Examination and Analysis The heat treatedand artificially aged Mg alloy specimens were sequentiallypolished by SiC coated abrasive papers (grit size 800 to1600) followed by polishing using 03 120583m Al

2O3pow-

der and ultrasonic cleaning in distilled water for 5minThe polished specimens were carefully etched in 2 Nitaletchant (ethanol HNO

3= 98mL 2mL) for 5 s with a peri-

odic assessment of surface microstructure for any sign ofacidic corrosion The microstructure of the Mg-Zn-Ca alloyspecimens was examined by scanning electron microscopy(SEM) (JSM-5900 JEOL Japan) (low magnification images)and by field emission scanning electron microscopy (FE-SEM) (SUPRA 40VP Carl Zeiss Co Ltd Germany) (highmagnification images) In addition the concentration of the

Advances in Materials Science and Engineering 3

Table 1 Details of the heat treatment parameters of the Mg-35Za-3Ca alloy

Type of treatment Group designation and treatment conditionsAT0 AT1 AT2 AT3 AT4

Solution treatment 310∘C 48 h 310∘C 48 h 310∘C 48 h 310∘C 48 h 310∘C 48 hAging treatment Untreated 170∘C 25 h 170∘C 50 h 170∘C 75 h 170∘C 10 h

elements present in the alloy and their distribution weredetermined using energy dispersive X-ray analysis (EDX)(Oxford England)

223 Potentiodynamic Polarization Test Potentiodynamicpolarization test was used to assess the electrochemicalcorrosion behavior of Mg-Zn-Ca alloy specimens An elec-trochemical cell consisting of AgAgCl KCl (satrsquod) as thereference electrode a platinum plate as the counter electrodeand Mg-Zn-Ca alloy specimens subjected to heat treatmentand artificial aging for different duration of time as theworking electrode connected to a potentiostatgalvanostat(273A EGampG PARC USA) was used for the study Theexperiments were performed with exposing the area 1 cm2in 150mL of Hanks solution whose chemical composition ispresented in Table 2 The potentiodynamic polarization testwas performed in the potential range minus05 V to +05V ata scan rate of 3mVs at room temperature The corrosionpotential (119864corr) and current density (119894corr) were calculatedfrom the measured polarization curves using Tafel extrapo-lation method followed by assessment of extent of corrosionthe specimens

224 Immersion Test The initial pH of the HBSS wasadjusted to 72 with the incremental additions of eitherNaOH (01molL) or HCl (01molL) using a pHmeter (HD-PHP Davis Co Ltd USA) The Mg-Zn-Ca alloy specimenssubjected to heat treatment and artificial aging for differentduration of time were immersed in 45mL of HBSS andincubated at 37∘C for 72 hThe change in pH of the HBSS wasmeasured as a function of immersion time

225 Measurement of Corrosion Rate The Mg-Zn-Ca alloyspecimens subjected to heat treatment and artificial agingfor different duration of time were immersed in 45mL ofHBSS and incubated at 37∘C for 5 days The HBSS wasreplaced every 24 h to suppress the change in concentrationof the solution during the test After 5 days of immersionthe Mg alloy specimens were rinsed in deionized waterand ultrasonically cleaned using isopropanol for 5min toremove the corrosion products attached to the specimenThe specimens were washed with distilled water and thendried To examine weight changes in the specimen caused bycorrosion the specimen weight was measured before and 5days after depositionThe corrosion rate was calculated usingthe following equation [23]

119862119877=119882

119860 times 119905 (1)

Table 2 Chemical composition of Hankrsquos balanced salt solution(HBSS)

Constituents Quantity (gL)Potassium phosphate monobasic [anhydrous] 006Sodium phosphate dibasic [anhydrous] 004788Potassium chloride 04Sodium chloride 80Phenol red Na 0011D-Glucose 10

where 119862119877is corrosion rate 119882 is weight loss 119860 is surface

area of the specimen exposed to the etching reagent and 119905is exposure time

226 Hemolysis Assessment The test solution used forhemolysis assessment was blood samples collected from thecoronary artery of rats which were treated with heparinand diluted with saline solution in a 4 5 ratio (vol)Specimens having a dimensions of 164mm diameter and2mm thickness from each experimental group were treatedwith 10mLof saline solution for 30min and the elutewas usedas the experimental group 10mL saline solution containing01 wt of Na

2CO3and 10mL saline solution were used

as the positive and negative control groups respectivelyEach 10mL solution of each group (experimental group andthe positive and negative control group) was mixed with02mL of the prepared test solution and incubated at 37∘Cfor 60min Subsequently each mixture was centrifuged at680G for 3min and 200120583L of the supernatant liquid wascollected Then absorbance was measured at 540 nm using amedical enzyme analyzer (Emax Molecular Devices USA)The measured absorbance was used to assess the percentagehemolysis by the following equation [24]

hemolysis () =OD (test) minusOD (negative)

OD (positive) minusOD (negative)times 100

(2)

3 Results

The SEM image of the microstructure of the as-cast Mg-35Zn-3Ca alloy etched using Nital for 5 s and its chemicalcomposition analyzed by EDX analysis are shown in Figure 1The microstructure of the alloy is homogeneous and revealsno casting defects The chemical composition of the alloyindicates the presence of Mg (6382wt) Zn (3263wt)

4 Advances in Materials Science and Engineering

(a)

100 200 300 400 500 600 700 800

Ca

Zn

MgLSecs 42

Zn

00

31

124

62

93

155

900

KCnt

Energy (keV)

(b)

Figure 1 SEM micrograph of as-cast Mg-35Zn-3Ca (a) and EDX spectrum results (b)

Table 3 Elemental composition of Mg-35Zn-3Ca alloy assessed byenergy dispersive X-ray analysis

Atomic Weight Ca 276 355Zn 1554 3263Mg Balance Balance

and Ca (355 wt) as the major elements (Table 3) suggest-ing that the alloy conforms to the chemical compositionrequirements of Mg-35Zn-3Ca alloy

The DSC trace of the as-cast Mg-35Zn-3Ca alloy speci-men is shown in Figure 2 The liquidus and solidus temper-atures are 36184∘C and 34011∘C respectively Based on thisresult the suitable temperature for solution heat treatment isset as 310∘C which is slightly lower than the solidus tempera-ture of the alloy Accordingly the as-cast Mg-35Zn-3Ca alloyis homogenized at 310∘C for 48 h and quenched in deionizedwater at room temperature to prevent any microsegregationand residual stress during precipitation (designated as AT0)Some of the specimens were subjected to artificial aging heattreatment at 170∘C for 25 50 75 and 100 h and designatedas AT1 AT2 AT3 and AT4 respectively

The SEM images of the surface microstructure of theheat-treated (AT0) and artificially aged (AT1 AT2 AT3 andAT4) Mg-35Zn-3Ca alloy specimens etched in Nital for 5 sare shown in Figure 3 Among all the specimens the AT2group exhibits the finest and most homogenous distributionof 120572 and 120573 phases It is also evident from Figure 3 thatwith increase in aging time the size of 120572 phase is increasedwith the disappearance of the boundary of 120573 phase resultingin a change in microstructure from a homogeneous to aninhomogeneous state The X-ray elemental mapping of MgZn and Ca along with the secondary electron image ofthe Mg-35Zn-3Ca alloy is shown in Figure 4 It is evidentthat the darker regions of the microstructure are mostlythe 120572-Mg matrix whereas the lighter regions are mainly the

240 260 280 300 320 340 360 380 400 420

00

02

34011

34556 36184

34973

Temperature (∘C)

minus02

minus04

minus06

minus08

Hea

t flow

(cal

(g s

))

Figure 2 DSC thermogram (heating curve) of as-cast Mg-35Zn-3Ca alloy

120573-phase precipitate which are relatively lower in Mg andlargely consist of zinc and calcium

The potentiodynamic polarization curves of heat-treated(AT0) and artificially aged (AT1 AT2 AT3 and AT4) Mg-35Zn-3Ca alloy specimens in HBSS are shown in Figure 5The119864corr and 119894corr values of all the specimens calculated usingTafel extrapolation method are compiled in Table 4 There isnot much variation in the 119864corr of all the specimens testedand all of them lie in the range of minus120 to minus129V versusAgAgClKCl (satrsquod) The 119894corr values of the specimens thatare heat-treated and artificially aged for different duration oftime (AT1 to AT4) are relatively higher than those subjectedonly for heat treatment (AT0) Among the heat treated andartificially aged samples (AT1 to AT4) specimens of the AT2group exhibit a lower 119894corr Based on the 119894corr values thecorrosion resistance of the Mg-35Zn-3Ca alloys specimenssubjected to only heat treatment (AT0) and heat treatmentfollowed by artificial aging for different duration of time (AT1to AT4) can be ranked as follows AT0 gt AT2 gt AT3 gt AT4 gtAT1

Advances in Materials Science and Engineering 5

(a) (b) (c)

(d) (e) (f)

(g) (h) (i)

(j) (k) (l)

(m) (n) (o)

Figure 3 Surface morphology of various heat treated Mg-35Zn-3Ca alloys (a) AT0 (times2000) (b) AT0 (times5000) (c) AT0 (times10000) (d) AT1(times2000) (e) AT1 (times5000) (f) AT1 (times10000) (g) AT2 (times2000) (h) AT2 (times5000) (i) AT2 (times10000) (j) AT3 (times2000) (k) AT3 (times5000) (l) AT3(times10000) (m) AT4 (times2000) (n) AT4 (times5000) and (o) AT4 (times10000)

6 Advances in Materials Science and Engineering

Table 4 Electrochemical corrosion parameters of Mg-35Zn-3Ca alloy in HBSS derived from the potentiodynamic polarization test usingTafel extrapolation method

GroupAT0 AT1 AT2 AT3 AT4

119864corr (V vs AgAgClKCl (satrsquod)) minus129 minus123 minus123 minus120 minus123119894corr (120583Acm

2) 1011 5091 3641 3751 4908

CaZn

Mg

Figure 4 Analysis of elemental composition on the surface by EDX mapping of Mg-35Zn-3Ca alloy

Pote

ntia

l (V

ver

sus A

gClK

Cl)

AT0AT1AT2

AT3AT4

minus11

minus12

minus13

minus141E minus 8 1E minus 7 1E minus 6 1E minus 5 1E minus 4 1E minus 3

Current density (Acm2)

Figure 5 Potentiodynamic polarization curve obtained in HBSSvarious heat treated Mg-35Zn-3Ca alloys

The change in pH of the HBSS in which the Mg-35Zn-3Ca alloys subjected to only heat treatment (AT0) and heattreatment followed by artificial aging for different durations(AT1 to AT4) are immersed measured for a duration of 72 his shown in Figure 6 In general all the specimens exhibita rapid increase in pH during the first 6 h beyond whichthe extent of increase in pH is decreased Beyond 48 h ofimmersion the pH of HBSS reached a stable value for all thespecimens studiedDuring the first 6 h of immersion theMg-35Zn-3Ca alloy specimens subjected to heat treatment alone(AT0) showed a rapid increase in pHwhen compared to thosesubjected to heat treatment followed by artificial aging fordifferent duration of time (AT1 to AT4) Among the AT1 toAT4 group specimens of the AT2 group showed a relativelyless increase in pH suggesting the lower extent of dissolutionof the Mg alloy

The corrosion rate of the Mg-35Zn-3Ca alloy specimenssubjected to only heat treatment (AT0) and heat treatmentfollowed by artificial aging for different duration of time (AT1to AT4) calculated using the loss in weight after immersionin HBSS at 37∘C for 5 days is shown in Figure 7 It is evident

Advances in Materials Science and Engineering 7

0 12 24 36 48 60 72

pH

Ageing time (hour)

7

8

9

10

11

AT0AT1AT2

AT3AT4

Figure 6 pH value as a function of immersion time

AT0 AT1 AT2 AT3 AT40

1

2

3

4

232

308308

373

Sample code

392

Cor

rosio

n ra

te (m

g(c

m2

day)

)

Figure 7 Corrosion rates of different heat treated Mg-35Zn-3Caalloys after immersion in HBSS for 5 days

that specimens subjected to heat treatment alone (AT0) showa higher corrosion rate (392mg(cm2 day)) when comparedto those subjected to heat treatment followed by artificialaging for different durations (AT1 to AT4) (ranging from232 to 373mg(cm2 day)) Among the AT1 to AT4 groupspecimens of the AT2 group showed a lower corrosion rate of232mg(cm2 day) which is significantly lower than those ofother groups (119875 lt 005)

In vitro hemolysis test is a well-known method to assessthe biotoxicity in a short duration of time The hemolysisability of Mg-35Zn-3Ca alloy specimens subjected to onlyheat treatment (AT0) and heat treatment followed by arti-ficial aging for different duration of time (AT1 to AT4) ismeasured using the positive (10mL saline solution containing01 wt of Na

2CO3) and negative (10mL saline solution)

as controls The measured optical density values and the

Table 5 Absorbance value measured at 540 nm and percentage ofhemolysis of Mg-35Zn-3Ca alloy subjected to heat treatment andartificial aging for different duration of time

Sample code OD at 540 nm Hemolysis ()AT0 0051 plusmn 0002 0515 plusmn 0375AT1 0050 plusmn 0002 0371 plusmn 0204AT2 0049 plusmn 0001 0147 plusmn 0104AT3 0050 plusmn 0001 0299 plusmn 0275AT4 0051 plusmn 0002 0521 plusmn 0272Negative 0049 plusmn 0001 0Positive 0495 plusmn 0013 100

hemolysis are compiled in Table 5 The variation in the hemolysis of all the samples tested alongwith the negative andpositive controls is plotted in Figure 8 for a better comparisonand to understand the statistical difference among themIt is evident from Table 5 and Figure 8 that among all thespecimens tested those belonging to the AT2 group showedthe lowest value of hemolysis (0147) However whencompared to other groups the difference in hemolysis isstatistically insignificant (119875 gt 005)

4 Discussion

Mg undergoes rapid corrosion in electrolytes containingchlorides such as body fluid Hence it will be difficult touse Mg for implant applications When Mg is exposed to airthe oxide layer formed on its surface offers only a partialprotection In aqueous solution the formation of porousMg(OH)

2layer could not offer much protection (equation

(3)) In presence of chloride ions it gets dissolved as MgCl2

while the aggressive nature of the medium causes severecorrosion of theMg (equations (4) and (5)) [25]The reactionsequences ofMg in aqueousmedium in the absence (equation(3)) and presence (equations (4) and (5)) of chloride ions canbe represented as follows [8]

Mg (solid) + 2H2O 997888rarr Mg (OH)

2+H2(gas) (3)

Mg (solid) + 2Clminus (aqueous) 997888rarr MgCl2

(4)

Mg (OH)2(solid) + 2Clminus 997888rarr MgCl

2 (5)

The corrosion resistance of Mg could be improvedthrough alloying formation of composites surface treat-ment and heat treatment [25ndash31] However the alloyingelements the second phase materials used to prepare thecomposites and the surface treated layer should not beharmful to the body when used as a biomaterial Someof the commonly used Mg-based alloys contain aluminumthat is harmful to the nervous system and osteoblasts whilethe RE-based Mg alloys could cause blood toxicity [1718] In the present study Mg-35Zn-3Ca alloy is preparedby adding zinc and calcium as alloying elements both ofwhich are nontoxic Alloying magnesium with zinc enablesprecipitation hardening while alloying with calcium couldhelp in grain refinement The microstructure and corrosion

8 Advances in Materials Science and Engineering

AT0 AT1 AT2 AT3 AT4 Negative Positive

0

1

2

90

100

05150371

01470299

0521

100

Hem

olys

is (

)

Sample code

0

Figure 8 Hemolysis percentage of various heat treated Mg-35Zn-3Ca alloys

resistance of the Mg-35Zn-3Ca alloy are evaluated aftersubjecting them to only heat treatment (AT0) and heattreatment and artificial aging for different duration of time(AT1 to AT4)

The microstructural examination after solution heattreatment and artificial aging heat treatment performed overa specific period of time showed that the 120572 and 120573 phaseswere finest and most homogenous in the AT2 group whichunderwent an artificial aging heat treatment at 170∘C for5 h Moreover the grain boundary was broken and 120573 phasewas inhomogeneous in the AT3 group which underwentartificial aging heat treatment for 75 h Results also showedthat the size of crystal grain became larger and the continuityof the crystal margin has disappeared in the AT4 groupwhich underwent artificial aging heat treatment for 10 h(Figure 3) Solution heat treatment is a process to preparethe supersaturated solid solution of unstable state materialsare generally softened by solution heat treatment Previousstudies have reported that artificial aging heat treatmentfollowing solution heat treatment of Mg alloy improvedstrength by refinement of the precipitate [29] Meanwhile itwas reported that heat treatment changed the microstruc-ture of alloy thereby affecting the corrosion behavior[32 33]

In this study potentiodynamic polarization studieschange in pH of HBSS and loss in weight after immersionin HBSS were used to assess the corrosion resistance of theMg-35Zn-3Ca alloy both in as-prepared and heat-treatedconditions The results of the potentiodynamic polarizationtest conducted to assess electrochemical corrosion behaviorshowed the lowest corrosion current density of 1011120583Acm2for the AT0 group which underwent only the solutionheat treatment Among the groups that underwent artificialaging following solution heat treatment the lowest corro-sion current density of 3641 120583Acm2 is observed for theAT2 group The corrosion current density which is closelyassociated with corrosion rate is an intersection point atwhich the negative Tafel slope is extrapolated to corrosionpotential by the Tafel extrapolation method [34] This resultshowed that corrosion resistance of the Mg-35Zn-3Ca alloy

is much improved for the group that underwent solution heattreatment alone than in groups that underwent artificial agingheat treatment following solution heat treatment Whenimmersed in HBSS Mg undergoes anodic dissolution withthe release of H

2gas and generation of OHminus ions resulting

in an increase in pH of the medium [35] These reactionsequences can be represented as follows [36]

Anodic reaction Mg 997888rarr Mg2+ + 2e (6)

Cathodic reaction 2H2O + 2e 997888rarr H

2+ 2OHminus (7)

Formation of corrosion product

Mg2+ + 2OHminus 997888rarr Mg (OH)2

(8)

Thus the rate of corrosion of MgMg alloys could beestimated from the change in pH of the corrosive medium(HBSS in this study) as a function of time The change inpH of the HBSS measured as a function of time (Figure 6)showed that it is slowest for specimens in the T2 group whencompared to other groups This inference indicates that thecorrosion resistance is increased as the microstructure ofthe surface gets finer and denser The loss in weight of thespecimens measured after 5 days of immersion in HBSS is232mg(cm2 day) for the AT2 group which is significantlylower than that of the other groups (119875 lt 005) The lossin weight is 392mg(cm2 day) for the AT0 group whichis the highest among all the specimens tested Howeverthe difference between the specimens is insignificant whencomparedwith the specimens in other groups except with theAT2 group (119875 gt 005) Hence it is clear that the specimens ofthe AT2 group have offered an excellent corrosion resistancewhich is consistent with the results of change in pHHoweverthe results are inconsistent with those of the potentiodynamicpolarization test The fineness and homogeneity of the 120573phase largely determine the corrosion behavior which isreflected in the pH variation and weight loss These resultssupported that corrosion behavior of magnesium alloyswith multiphase structure is changed according to corro-sion potential difference distribution and volume fractionbetween micr-constituent phases [16 37 38] Since thesemeasurements are made for a long term the ability of the120573 phase to act as a physical barrier for corrosion becomeseffective [33 39] However during the electrochemical studysince the test is performed over a short duration the effect isnot reflected [29]

The hemolysis test which is conducted to assess thetoxicity to the body uses the principle that red blood cellsare divided or necrotized when the hemoglobin is destroyedThe concentration of free hemoglobin is proportional to thenumber of the injured RBC and the volume of the fluid [2440] The results of hemolysis test showed that the percentageof hemolysis (0147) in AT2 group is the lowest among allthe samples tested and when compared with other groups nostatistical significance difference could be observed (Figure 8Table 5) (119875 gt 005) In general if the hemolysis value is 5or less then it is considered as nonhemolytic according to

Advances in Materials Science and Engineering 9

ISO 10993-42002 [41] Accordingly the composition of Mg-35Zn-3Ca has low hemolysis and analogies good biocompat-ibility In other words homogenization and aging process ofthe Mg-35Zn-3Ca alloy can improve the physical propertiesand corrosion resistance of the material and it does not havea significant effect on the hemolytic toxicity

5 Conclusions

The preparation of Mg-35Zn-3Ca alloy containing zinc andcalcium rather than aluminum or RE elements as nontoxicand biocompatible alloying elements followed by heat treat-ment and artificial aging of the alloy to control its rate ofdegradation is reported The study leads to the followingconclusions

(1) DSC studies showed that the liquidus and solidustemperatures of the Mg-35Zn-3Ca alloy were36184∘C and 34011∘C respectively

(2) The microstructural features of the Mg-35Zn-3Caalloy indicate the presence of 120572-Mg matrix and 120573phase after heat treatment and artificial aging forvarious duration of time Among them the AT2group (heat treatment at 170∘C for 5 h followed byartificial aging at 310∘C for 48 h) exhibits the finest andmost homogenous distribution of 120572 and 120573 phases

(3) Potentiodynamic polarization studies of the Mg-35Zn-3Ca alloy specimens indicate that the 119894corr valuesof specimens that are heat-treated and artificiallyaged for different duration of time (AT1 to AT4) arerelatively higher than those subjected only to heattreatment (AT0) Among heat-treated and artificiallyaged samples (AT1 to AT4) specimens of the AT2group exhibit a lower 119894corr Based on the 119894corr valuesthe specimens can be ranked as follows AT0 gtAT2 gtAT3 gt AT4 gt AT1

(4) The change in pH of theHBSSmeasured for 72 h indi-cates that all the specimens exhibit a rapid increase inpH during the first 6 h during which the Mg-35Zn-3Ca alloy specimens subjected to heat treatment alone(AT0) showed a rapid increase in pH Beyond 48 hof immersion the pH of HBSS reached a stable valuefor all the specimens studied Among the AT1 toAT4 groups specimens of the AT2 group showed arelatively less increase in pH suggesting the lowerextent of dissolution of the Mg alloy

(5) Mg-35Zn-3Ca alloy specimens subjected to heattreatment alone (AT0) showed a corrosion rate of392mg(cm2 day) than those subjected to heat treat-ment followed by artificial aging for different dura-tions (AT1 to AT4) which ranges between 232 and373mg(cm2 day) Among the AT1 to AT4 groupsspecimens of theAT2 group showed a lower corrosionrate of 232mg(cm2 day) which is significantly lowerthan those of other groups (119875 lt 005)

(6) In vitro hemolysis test showed the lowest hemolysispercentage value of 0147 for the AT2 group but

the differences were statistically insignificant whencompared with that of other groups (119875 lt 005) Thehemolysis was 5 or less for all groups which indi-cates no significant hemoglobin destruction whichsuggests that Mg-35Zn-3Ca alloy has no cytotoxicity

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Authorsrsquo Contribution

Il-Song Park contributed to this work and is considered asjoint first author

Acknowledgments

This work was supported by the National Research Founda-tion of Korea (NRF) Grant funded by the Korea government(MSIP) (no 2011-0028709 and no 2014R1A4A1005309) andRegional Strategic Industry project (2013-R0002274)

References

[1] D A Puleo and W W Huh ldquoAcute toxicity of metal ions incultures of osteogenic cells derived from bone marrow stromalcellsrdquo Journal of Applied Biomaterials vol 6 no 2 pp 109ndash1161995

[2] J J Jacobs J L Gilbert and R M Urban ldquoCurrent conceptsreview Corrosion of metal orthopaedic implantsrdquo The Journalof Bone amp Joint Surgery vol 80 pp 268ndash282 1998

[3] C Lhotka T Szekeres I Steffan K Zhuber and K ZweymullerldquoFour-year study of cobalt and chromium blood levels inpatients managed with two different metal-on-metal total hipreplacementsrdquo Journal of Orthopaedic Research vol 21 no 2pp 189ndash195 2003

[4] J J Jacobs A K Skipor L M Patterson et al ldquoMetal releasein patients who have had a primary total hip arthroplasty Aprospective controlled longitudinal studyrdquoThe Journal of Boneand Joint SurgerymdashAmerican Volume vol 80 no 10 pp 1447ndash1458 1998

[5] J J Jacobs N J Hallab A K Skipor and R M UrbanldquoMetal degradation products a cause for concern in metal-metal bearingsrdquo Clinical Orthopaedics and Related Researchno 417 pp 139ndash147 2003

[6] J Nagels M Stokdijk and P M Rozing ldquoStress shielding andbone resorption in shoulder arthroplastyrdquo Journal of Shoulderand Elbow Surgery vol 12 no 1 pp 35ndash39 2003

[7] H G Seiler H Sigel and A Sigel Handbook on Toxicity ofInorganic Compounds 1988

[8] M P Staiger A M Pietak J Huadmai and G Dias ldquoMag-nesium and its alloys as orthopedic biomaterials a reviewrdquoBiomaterials vol 27 no 9 pp 1728ndash1734 2006

[9] E P DeGarmo J T Black and R A Kohser DeGarmorsquosMaterials and Processes in Manufacturing John Wiley amp Sons2011

[10] L J Gibson and M F Ashby Cellular Solids Structure andProperties Cambridge University Press 1999

10 Advances in Materials Science and Engineering

[11] J-W Choi Y-M Kong H-E Kim and I-S Lee ldquoReinforce-ment of hydroxyapatite bioceramic by addition of Ni

3

Al andAl2

O3

rdquo Journal of the American Ceramic Society vol 81 no 7pp 1743ndash1748 1998

[12] T Thamaraiselvi and S Rajeswari ldquoBiological evaluation ofbioceramic materialsmdasha reviewrdquo Trends in Biomaterials andArtificial Organs vol 18 no 1 pp 9ndash17 2004

[13] H Zreiqat C R Howlett A Zannettino et al ldquoMechanismsof magnesium-stimulated adhesion of osteoblastic cells tocommonly used orthopaedic implantsrdquo Journal of BiomedicalMaterials Research vol 62 no 2 pp 175ndash184 2002

[14] F Witte V Kaese H Haferkamp et al ldquoIn vivo corrosionof four magnesium alloys and the associated bone responserdquoBiomaterials vol 26 no 17 pp 3557ndash3563 2005

[15] C EWenMMabuchi Y Yamada K Shimojima Y Chino andT Asahina ldquoProcessing of biocompatible porous Ti and MgrdquoScripta Materialia vol 45 no 10 pp 1147ndash1153 2001

[16] G Song ldquoRecent progress in corrosion and protection ofmagnesium alloysrdquo Advanced Engineering Materials vol 7 no7 pp 563ndash586 2005

[17] S S A El-Rahman ldquoNeuropathology of aluminum toxicityin rats (glutamate and GABA impairment)rdquo PharmacologicalResearch vol 47 no 3 pp 189ndash194 2003

[18] Y Nakamura Y Tsumura Y Tonogai T Shibata and Y ItoldquoDifferences in behavior among the chlorides of seven rare earthelements administered intravenously to ratsrdquo Toxicological Sci-ences vol 37 no 2 pp 106ndash116 1997

[19] J Z Ilich and J E Kerstetter ldquoNutrition in bone health revisiteda story beyond calciumrdquo Journal of the American College ofNutrition vol 19 no 6 pp 715ndash737 2000

[20] J C Oh T Ohkubo T Mukai and K Hono ldquoTEM and 3DAPcharacterization of an age-hardened Mg-Ca-Zn alloyrdquo ScriptaMaterialia vol 53 no 6 pp 675ndash679 2005

[21] G Levi S Avraham A Zilberov and M Bamberger ldquoSolidifi-cation solution treatment and age hardening of a Mg-16 wtCa-32 wt Zn alloyrdquo Acta Materialia vol 54 no 2 pp 523ndash530 2006

[22] T Miyazaki J Kaneko and M Sugamata ldquoStructures andproperties of rapidly solidified Mg-Ca based alloysrdquo MaterialsScience and Engineering A vol 181-182 pp 1410ndash1414 1994

[23] C Liu Y Xin G Tang and P K Chu ldquoInfluence of heattreatment on degradation behavior of bio-degradable die-castAZ63 magnesium alloy in simulated body fluidrdquo MaterialsScience and Engineering A vol 456 no 1-2 pp 350ndash357 2007

[24] X Gu Y Zheng Y Cheng S Zhong and T Xi ldquoIn vitrocorrosion and biocompatibility of binary magnesium alloysrdquoBiomaterials vol 30 no 4 pp 484ndash498 2009

[25] B A Shaw Corrosion Resistance of Magnesium Alloys vol 13ASM handbook 2003

[26] V Kaesel P T Tai F Bach H Haferkamp F Witte and HWindhagen ldquoApproach to control the corrosion of magnesiumby alloyingrdquo inMagnesium Proceedings of the 6th InternationalConference Magnesium Alloys and Their Applications pp 534ndash539 Wiley Online Library 2004

[27] J E Gray and B Luan ldquoProtective coatings on magnesium andits alloysmdasha critical reviewrdquo Journal of Alloys and Compoundsvol 336 no 1-2 pp 88ndash113 2002

[28] M-C Zhao M Liu G Song and A Atrens ldquoInfluence of the120573-phase morphology on the corrosion of the Mg alloy AZ91rdquoCorrosion Science vol 50 no 7 pp 1939ndash1953 2008

[29] N N Aung andW Zhou ldquoEffect of heat treatment on corrosionand electrochemical behaviour of AZ91D magnesium alloyrdquoJournal of Applied Electrochemistry vol 32 no 12 pp 1397ndash14012002

[30] G Song A L Bowles and D H StJohn ldquoCorrosion resistanceof aged die cast magnesium alloy AZ91DrdquoMaterials Science andEngineering A vol 366 no 1 pp 74ndash86 2004

[31] M Jonsson D Persson and R Gubner ldquoThe initial steps ofatmospheric corrosion on magnesium alloy AZ91Drdquo Journal ofthe Electrochemical Society vol 154 no 11 pp C684ndashC691 2007

[32] T Beldjoudi C Fiaud and L Robbiola ldquoInfluence of homog-enization and artificial aging heat treatments on corrosionbehavior of Mg-Al alloysrdquo Corrosion vol 49 no 9 pp 738ndash7451993

[33] O Lunder J E Lein T K Aune and K Nisancioglu ldquoRole ofMg17Al12 phase in the corrosion of Mg alloy AZ91rdquo Corrosionvol 45 no 9 pp 741ndash748 1989

[34] D L Piron The Electrochemistry of Corrosion University ofHouston Houston Tex USA 1991

[35] G Song A Atrens D Stjohn J Nairn and Y Li ldquoThe electro-chemical corrosion of pure magnesium in 1 N NaClrdquo CorrosionScience vol 39 no 5 pp 855ndash875 1997

[36] Z Li X Gu S Lou and Y Zheng ldquoThe development of binaryMg-Ca alloys for use as biodegradable materials within bonerdquoBiomaterials vol 29 no 10 pp 1329ndash1344 2008

[37] A E Coy F Viejo P Skeldon and G E Thompson ldquoSus-ceptibility of rare-earth-magnesium alloys to micro-galvaniccorrosionrdquo Corrosion Science vol 52 no 12 pp 3896ndash39062010

[38] G Song and A Atrens ldquoUnderstanding magnesiumcorrosionmdasha framework for improved alloy performancerdquoAdvanced Engineering Materials vol 5 no 12 pp 837ndash8582003

[39] A F Crawley and K S Milliken ldquoPrecipitate morphology andorientation relationships in an agedMg-9Al-1 Zn-03Mnalloyrdquo Acta Metallurgica vol 22 no 5 pp 557ndash562 1974

[40] S O Sowemimo-Coker ldquoRed blood cell hemolysis duringprocessingrdquoTransfusionMedicine Reviews vol 16 no 1 pp 46ndash60 2002

[41] ISO ldquoBiological evaluation of medical devicesmdashPart 4 selec-tion of tests for interactions with bloodrdquo Tech Rep ISO 10993-4 2002

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CeramicsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CompositesJournal of

NanoparticlesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Biomaterials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MetallurgyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

MaterialsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nano

materials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofNanomaterials

Advances in Materials Science and Engineering 3

Table 1 Details of the heat treatment parameters of the Mg-35Za-3Ca alloy

Type of treatment Group designation and treatment conditionsAT0 AT1 AT2 AT3 AT4

Solution treatment 310∘C 48 h 310∘C 48 h 310∘C 48 h 310∘C 48 h 310∘C 48 hAging treatment Untreated 170∘C 25 h 170∘C 50 h 170∘C 75 h 170∘C 10 h

elements present in the alloy and their distribution weredetermined using energy dispersive X-ray analysis (EDX)(Oxford England)

223 Potentiodynamic Polarization Test Potentiodynamicpolarization test was used to assess the electrochemicalcorrosion behavior of Mg-Zn-Ca alloy specimens An elec-trochemical cell consisting of AgAgCl KCl (satrsquod) as thereference electrode a platinum plate as the counter electrodeand Mg-Zn-Ca alloy specimens subjected to heat treatmentand artificial aging for different duration of time as theworking electrode connected to a potentiostatgalvanostat(273A EGampG PARC USA) was used for the study Theexperiments were performed with exposing the area 1 cm2in 150mL of Hanks solution whose chemical composition ispresented in Table 2 The potentiodynamic polarization testwas performed in the potential range minus05 V to +05V ata scan rate of 3mVs at room temperature The corrosionpotential (119864corr) and current density (119894corr) were calculatedfrom the measured polarization curves using Tafel extrapo-lation method followed by assessment of extent of corrosionthe specimens

224 Immersion Test The initial pH of the HBSS wasadjusted to 72 with the incremental additions of eitherNaOH (01molL) or HCl (01molL) using a pHmeter (HD-PHP Davis Co Ltd USA) The Mg-Zn-Ca alloy specimenssubjected to heat treatment and artificial aging for differentduration of time were immersed in 45mL of HBSS andincubated at 37∘C for 72 hThe change in pH of the HBSS wasmeasured as a function of immersion time

225 Measurement of Corrosion Rate The Mg-Zn-Ca alloyspecimens subjected to heat treatment and artificial agingfor different duration of time were immersed in 45mL ofHBSS and incubated at 37∘C for 5 days The HBSS wasreplaced every 24 h to suppress the change in concentrationof the solution during the test After 5 days of immersionthe Mg alloy specimens were rinsed in deionized waterand ultrasonically cleaned using isopropanol for 5min toremove the corrosion products attached to the specimenThe specimens were washed with distilled water and thendried To examine weight changes in the specimen caused bycorrosion the specimen weight was measured before and 5days after depositionThe corrosion rate was calculated usingthe following equation [23]

119862119877=119882

119860 times 119905 (1)

Table 2 Chemical composition of Hankrsquos balanced salt solution(HBSS)

Constituents Quantity (gL)Potassium phosphate monobasic [anhydrous] 006Sodium phosphate dibasic [anhydrous] 004788Potassium chloride 04Sodium chloride 80Phenol red Na 0011D-Glucose 10

where 119862119877is corrosion rate 119882 is weight loss 119860 is surface

area of the specimen exposed to the etching reagent and 119905is exposure time

226 Hemolysis Assessment The test solution used forhemolysis assessment was blood samples collected from thecoronary artery of rats which were treated with heparinand diluted with saline solution in a 4 5 ratio (vol)Specimens having a dimensions of 164mm diameter and2mm thickness from each experimental group were treatedwith 10mLof saline solution for 30min and the elutewas usedas the experimental group 10mL saline solution containing01 wt of Na

2CO3and 10mL saline solution were used

as the positive and negative control groups respectivelyEach 10mL solution of each group (experimental group andthe positive and negative control group) was mixed with02mL of the prepared test solution and incubated at 37∘Cfor 60min Subsequently each mixture was centrifuged at680G for 3min and 200120583L of the supernatant liquid wascollected Then absorbance was measured at 540 nm using amedical enzyme analyzer (Emax Molecular Devices USA)The measured absorbance was used to assess the percentagehemolysis by the following equation [24]

hemolysis () =OD (test) minusOD (negative)

OD (positive) minusOD (negative)times 100

(2)

3 Results

The SEM image of the microstructure of the as-cast Mg-35Zn-3Ca alloy etched using Nital for 5 s and its chemicalcomposition analyzed by EDX analysis are shown in Figure 1The microstructure of the alloy is homogeneous and revealsno casting defects The chemical composition of the alloyindicates the presence of Mg (6382wt) Zn (3263wt)

4 Advances in Materials Science and Engineering

(a)

100 200 300 400 500 600 700 800

Ca

Zn

MgLSecs 42

Zn

00

31

124

62

93

155

900

KCnt

Energy (keV)

(b)

Figure 1 SEM micrograph of as-cast Mg-35Zn-3Ca (a) and EDX spectrum results (b)

Table 3 Elemental composition of Mg-35Zn-3Ca alloy assessed byenergy dispersive X-ray analysis

Atomic Weight Ca 276 355Zn 1554 3263Mg Balance Balance

and Ca (355 wt) as the major elements (Table 3) suggest-ing that the alloy conforms to the chemical compositionrequirements of Mg-35Zn-3Ca alloy

The DSC trace of the as-cast Mg-35Zn-3Ca alloy speci-men is shown in Figure 2 The liquidus and solidus temper-atures are 36184∘C and 34011∘C respectively Based on thisresult the suitable temperature for solution heat treatment isset as 310∘C which is slightly lower than the solidus tempera-ture of the alloy Accordingly the as-cast Mg-35Zn-3Ca alloyis homogenized at 310∘C for 48 h and quenched in deionizedwater at room temperature to prevent any microsegregationand residual stress during precipitation (designated as AT0)Some of the specimens were subjected to artificial aging heattreatment at 170∘C for 25 50 75 and 100 h and designatedas AT1 AT2 AT3 and AT4 respectively

The SEM images of the surface microstructure of theheat-treated (AT0) and artificially aged (AT1 AT2 AT3 andAT4) Mg-35Zn-3Ca alloy specimens etched in Nital for 5 sare shown in Figure 3 Among all the specimens the AT2group exhibits the finest and most homogenous distributionof 120572 and 120573 phases It is also evident from Figure 3 thatwith increase in aging time the size of 120572 phase is increasedwith the disappearance of the boundary of 120573 phase resultingin a change in microstructure from a homogeneous to aninhomogeneous state The X-ray elemental mapping of MgZn and Ca along with the secondary electron image ofthe Mg-35Zn-3Ca alloy is shown in Figure 4 It is evidentthat the darker regions of the microstructure are mostlythe 120572-Mg matrix whereas the lighter regions are mainly the

240 260 280 300 320 340 360 380 400 420

00

02

34011

34556 36184

34973

Temperature (∘C)

minus02

minus04

minus06

minus08

Hea

t flow

(cal

(g s

))

Figure 2 DSC thermogram (heating curve) of as-cast Mg-35Zn-3Ca alloy

120573-phase precipitate which are relatively lower in Mg andlargely consist of zinc and calcium

The potentiodynamic polarization curves of heat-treated(AT0) and artificially aged (AT1 AT2 AT3 and AT4) Mg-35Zn-3Ca alloy specimens in HBSS are shown in Figure 5The119864corr and 119894corr values of all the specimens calculated usingTafel extrapolation method are compiled in Table 4 There isnot much variation in the 119864corr of all the specimens testedand all of them lie in the range of minus120 to minus129V versusAgAgClKCl (satrsquod) The 119894corr values of the specimens thatare heat-treated and artificially aged for different duration oftime (AT1 to AT4) are relatively higher than those subjectedonly for heat treatment (AT0) Among the heat treated andartificially aged samples (AT1 to AT4) specimens of the AT2group exhibit a lower 119894corr Based on the 119894corr values thecorrosion resistance of the Mg-35Zn-3Ca alloys specimenssubjected to only heat treatment (AT0) and heat treatmentfollowed by artificial aging for different duration of time (AT1to AT4) can be ranked as follows AT0 gt AT2 gt AT3 gt AT4 gtAT1

Advances in Materials Science and Engineering 5

(a) (b) (c)

(d) (e) (f)

(g) (h) (i)

(j) (k) (l)

(m) (n) (o)

Figure 3 Surface morphology of various heat treated Mg-35Zn-3Ca alloys (a) AT0 (times2000) (b) AT0 (times5000) (c) AT0 (times10000) (d) AT1(times2000) (e) AT1 (times5000) (f) AT1 (times10000) (g) AT2 (times2000) (h) AT2 (times5000) (i) AT2 (times10000) (j) AT3 (times2000) (k) AT3 (times5000) (l) AT3(times10000) (m) AT4 (times2000) (n) AT4 (times5000) and (o) AT4 (times10000)

6 Advances in Materials Science and Engineering

Table 4 Electrochemical corrosion parameters of Mg-35Zn-3Ca alloy in HBSS derived from the potentiodynamic polarization test usingTafel extrapolation method

GroupAT0 AT1 AT2 AT3 AT4

119864corr (V vs AgAgClKCl (satrsquod)) minus129 minus123 minus123 minus120 minus123119894corr (120583Acm

2) 1011 5091 3641 3751 4908

CaZn

Mg

Figure 4 Analysis of elemental composition on the surface by EDX mapping of Mg-35Zn-3Ca alloy

Pote

ntia

l (V

ver

sus A

gClK

Cl)

AT0AT1AT2

AT3AT4

minus11

minus12

minus13

minus141E minus 8 1E minus 7 1E minus 6 1E minus 5 1E minus 4 1E minus 3

Current density (Acm2)

Figure 5 Potentiodynamic polarization curve obtained in HBSSvarious heat treated Mg-35Zn-3Ca alloys

The change in pH of the HBSS in which the Mg-35Zn-3Ca alloys subjected to only heat treatment (AT0) and heattreatment followed by artificial aging for different durations(AT1 to AT4) are immersed measured for a duration of 72 his shown in Figure 6 In general all the specimens exhibita rapid increase in pH during the first 6 h beyond whichthe extent of increase in pH is decreased Beyond 48 h ofimmersion the pH of HBSS reached a stable value for all thespecimens studiedDuring the first 6 h of immersion theMg-35Zn-3Ca alloy specimens subjected to heat treatment alone(AT0) showed a rapid increase in pHwhen compared to thosesubjected to heat treatment followed by artificial aging fordifferent duration of time (AT1 to AT4) Among the AT1 toAT4 group specimens of the AT2 group showed a relativelyless increase in pH suggesting the lower extent of dissolutionof the Mg alloy

The corrosion rate of the Mg-35Zn-3Ca alloy specimenssubjected to only heat treatment (AT0) and heat treatmentfollowed by artificial aging for different duration of time (AT1to AT4) calculated using the loss in weight after immersionin HBSS at 37∘C for 5 days is shown in Figure 7 It is evident

Advances in Materials Science and Engineering 7

0 12 24 36 48 60 72

pH

Ageing time (hour)

7

8

9

10

11

AT0AT1AT2

AT3AT4

Figure 6 pH value as a function of immersion time

AT0 AT1 AT2 AT3 AT40

1

2

3

4

232

308308

373

Sample code

392

Cor

rosio

n ra

te (m

g(c

m2

day)

)

Figure 7 Corrosion rates of different heat treated Mg-35Zn-3Caalloys after immersion in HBSS for 5 days

that specimens subjected to heat treatment alone (AT0) showa higher corrosion rate (392mg(cm2 day)) when comparedto those subjected to heat treatment followed by artificialaging for different durations (AT1 to AT4) (ranging from232 to 373mg(cm2 day)) Among the AT1 to AT4 groupspecimens of the AT2 group showed a lower corrosion rate of232mg(cm2 day) which is significantly lower than those ofother groups (119875 lt 005)

In vitro hemolysis test is a well-known method to assessthe biotoxicity in a short duration of time The hemolysisability of Mg-35Zn-3Ca alloy specimens subjected to onlyheat treatment (AT0) and heat treatment followed by arti-ficial aging for different duration of time (AT1 to AT4) ismeasured using the positive (10mL saline solution containing01 wt of Na

2CO3) and negative (10mL saline solution)

as controls The measured optical density values and the

Table 5 Absorbance value measured at 540 nm and percentage ofhemolysis of Mg-35Zn-3Ca alloy subjected to heat treatment andartificial aging for different duration of time

Sample code OD at 540 nm Hemolysis ()AT0 0051 plusmn 0002 0515 plusmn 0375AT1 0050 plusmn 0002 0371 plusmn 0204AT2 0049 plusmn 0001 0147 plusmn 0104AT3 0050 plusmn 0001 0299 plusmn 0275AT4 0051 plusmn 0002 0521 plusmn 0272Negative 0049 plusmn 0001 0Positive 0495 plusmn 0013 100

hemolysis are compiled in Table 5 The variation in the hemolysis of all the samples tested alongwith the negative andpositive controls is plotted in Figure 8 for a better comparisonand to understand the statistical difference among themIt is evident from Table 5 and Figure 8 that among all thespecimens tested those belonging to the AT2 group showedthe lowest value of hemolysis (0147) However whencompared to other groups the difference in hemolysis isstatistically insignificant (119875 gt 005)

4 Discussion

Mg undergoes rapid corrosion in electrolytes containingchlorides such as body fluid Hence it will be difficult touse Mg for implant applications When Mg is exposed to airthe oxide layer formed on its surface offers only a partialprotection In aqueous solution the formation of porousMg(OH)

2layer could not offer much protection (equation

(3)) In presence of chloride ions it gets dissolved as MgCl2

while the aggressive nature of the medium causes severecorrosion of theMg (equations (4) and (5)) [25]The reactionsequences ofMg in aqueousmedium in the absence (equation(3)) and presence (equations (4) and (5)) of chloride ions canbe represented as follows [8]

Mg (solid) + 2H2O 997888rarr Mg (OH)

2+H2(gas) (3)

Mg (solid) + 2Clminus (aqueous) 997888rarr MgCl2

(4)

Mg (OH)2(solid) + 2Clminus 997888rarr MgCl

2 (5)

The corrosion resistance of Mg could be improvedthrough alloying formation of composites surface treat-ment and heat treatment [25ndash31] However the alloyingelements the second phase materials used to prepare thecomposites and the surface treated layer should not beharmful to the body when used as a biomaterial Someof the commonly used Mg-based alloys contain aluminumthat is harmful to the nervous system and osteoblasts whilethe RE-based Mg alloys could cause blood toxicity [1718] In the present study Mg-35Zn-3Ca alloy is preparedby adding zinc and calcium as alloying elements both ofwhich are nontoxic Alloying magnesium with zinc enablesprecipitation hardening while alloying with calcium couldhelp in grain refinement The microstructure and corrosion

8 Advances in Materials Science and Engineering

AT0 AT1 AT2 AT3 AT4 Negative Positive

0

1

2

90

100

05150371

01470299

0521

100

Hem

olys

is (

)

Sample code

0

Figure 8 Hemolysis percentage of various heat treated Mg-35Zn-3Ca alloys

resistance of the Mg-35Zn-3Ca alloy are evaluated aftersubjecting them to only heat treatment (AT0) and heattreatment and artificial aging for different duration of time(AT1 to AT4)

The microstructural examination after solution heattreatment and artificial aging heat treatment performed overa specific period of time showed that the 120572 and 120573 phaseswere finest and most homogenous in the AT2 group whichunderwent an artificial aging heat treatment at 170∘C for5 h Moreover the grain boundary was broken and 120573 phasewas inhomogeneous in the AT3 group which underwentartificial aging heat treatment for 75 h Results also showedthat the size of crystal grain became larger and the continuityof the crystal margin has disappeared in the AT4 groupwhich underwent artificial aging heat treatment for 10 h(Figure 3) Solution heat treatment is a process to preparethe supersaturated solid solution of unstable state materialsare generally softened by solution heat treatment Previousstudies have reported that artificial aging heat treatmentfollowing solution heat treatment of Mg alloy improvedstrength by refinement of the precipitate [29] Meanwhile itwas reported that heat treatment changed the microstruc-ture of alloy thereby affecting the corrosion behavior[32 33]

In this study potentiodynamic polarization studieschange in pH of HBSS and loss in weight after immersionin HBSS were used to assess the corrosion resistance of theMg-35Zn-3Ca alloy both in as-prepared and heat-treatedconditions The results of the potentiodynamic polarizationtest conducted to assess electrochemical corrosion behaviorshowed the lowest corrosion current density of 1011120583Acm2for the AT0 group which underwent only the solutionheat treatment Among the groups that underwent artificialaging following solution heat treatment the lowest corro-sion current density of 3641 120583Acm2 is observed for theAT2 group The corrosion current density which is closelyassociated with corrosion rate is an intersection point atwhich the negative Tafel slope is extrapolated to corrosionpotential by the Tafel extrapolation method [34] This resultshowed that corrosion resistance of the Mg-35Zn-3Ca alloy

is much improved for the group that underwent solution heattreatment alone than in groups that underwent artificial agingheat treatment following solution heat treatment Whenimmersed in HBSS Mg undergoes anodic dissolution withthe release of H

2gas and generation of OHminus ions resulting

in an increase in pH of the medium [35] These reactionsequences can be represented as follows [36]

Anodic reaction Mg 997888rarr Mg2+ + 2e (6)

Cathodic reaction 2H2O + 2e 997888rarr H

2+ 2OHminus (7)

Formation of corrosion product

Mg2+ + 2OHminus 997888rarr Mg (OH)2

(8)

Thus the rate of corrosion of MgMg alloys could beestimated from the change in pH of the corrosive medium(HBSS in this study) as a function of time The change inpH of the HBSS measured as a function of time (Figure 6)showed that it is slowest for specimens in the T2 group whencompared to other groups This inference indicates that thecorrosion resistance is increased as the microstructure ofthe surface gets finer and denser The loss in weight of thespecimens measured after 5 days of immersion in HBSS is232mg(cm2 day) for the AT2 group which is significantlylower than that of the other groups (119875 lt 005) The lossin weight is 392mg(cm2 day) for the AT0 group whichis the highest among all the specimens tested Howeverthe difference between the specimens is insignificant whencomparedwith the specimens in other groups except with theAT2 group (119875 gt 005) Hence it is clear that the specimens ofthe AT2 group have offered an excellent corrosion resistancewhich is consistent with the results of change in pHHoweverthe results are inconsistent with those of the potentiodynamicpolarization test The fineness and homogeneity of the 120573phase largely determine the corrosion behavior which isreflected in the pH variation and weight loss These resultssupported that corrosion behavior of magnesium alloyswith multiphase structure is changed according to corro-sion potential difference distribution and volume fractionbetween micr-constituent phases [16 37 38] Since thesemeasurements are made for a long term the ability of the120573 phase to act as a physical barrier for corrosion becomeseffective [33 39] However during the electrochemical studysince the test is performed over a short duration the effect isnot reflected [29]

The hemolysis test which is conducted to assess thetoxicity to the body uses the principle that red blood cellsare divided or necrotized when the hemoglobin is destroyedThe concentration of free hemoglobin is proportional to thenumber of the injured RBC and the volume of the fluid [2440] The results of hemolysis test showed that the percentageof hemolysis (0147) in AT2 group is the lowest among allthe samples tested and when compared with other groups nostatistical significance difference could be observed (Figure 8Table 5) (119875 gt 005) In general if the hemolysis value is 5or less then it is considered as nonhemolytic according to

Advances in Materials Science and Engineering 9

ISO 10993-42002 [41] Accordingly the composition of Mg-35Zn-3Ca has low hemolysis and analogies good biocompat-ibility In other words homogenization and aging process ofthe Mg-35Zn-3Ca alloy can improve the physical propertiesand corrosion resistance of the material and it does not havea significant effect on the hemolytic toxicity

5 Conclusions

The preparation of Mg-35Zn-3Ca alloy containing zinc andcalcium rather than aluminum or RE elements as nontoxicand biocompatible alloying elements followed by heat treat-ment and artificial aging of the alloy to control its rate ofdegradation is reported The study leads to the followingconclusions

(1) DSC studies showed that the liquidus and solidustemperatures of the Mg-35Zn-3Ca alloy were36184∘C and 34011∘C respectively

(2) The microstructural features of the Mg-35Zn-3Caalloy indicate the presence of 120572-Mg matrix and 120573phase after heat treatment and artificial aging forvarious duration of time Among them the AT2group (heat treatment at 170∘C for 5 h followed byartificial aging at 310∘C for 48 h) exhibits the finest andmost homogenous distribution of 120572 and 120573 phases

(3) Potentiodynamic polarization studies of the Mg-35Zn-3Ca alloy specimens indicate that the 119894corr valuesof specimens that are heat-treated and artificiallyaged for different duration of time (AT1 to AT4) arerelatively higher than those subjected only to heattreatment (AT0) Among heat-treated and artificiallyaged samples (AT1 to AT4) specimens of the AT2group exhibit a lower 119894corr Based on the 119894corr valuesthe specimens can be ranked as follows AT0 gtAT2 gtAT3 gt AT4 gt AT1

(4) The change in pH of theHBSSmeasured for 72 h indi-cates that all the specimens exhibit a rapid increase inpH during the first 6 h during which the Mg-35Zn-3Ca alloy specimens subjected to heat treatment alone(AT0) showed a rapid increase in pH Beyond 48 hof immersion the pH of HBSS reached a stable valuefor all the specimens studied Among the AT1 toAT4 groups specimens of the AT2 group showed arelatively less increase in pH suggesting the lowerextent of dissolution of the Mg alloy

(5) Mg-35Zn-3Ca alloy specimens subjected to heattreatment alone (AT0) showed a corrosion rate of392mg(cm2 day) than those subjected to heat treat-ment followed by artificial aging for different dura-tions (AT1 to AT4) which ranges between 232 and373mg(cm2 day) Among the AT1 to AT4 groupsspecimens of theAT2 group showed a lower corrosionrate of 232mg(cm2 day) which is significantly lowerthan those of other groups (119875 lt 005)

(6) In vitro hemolysis test showed the lowest hemolysispercentage value of 0147 for the AT2 group but

the differences were statistically insignificant whencompared with that of other groups (119875 lt 005) Thehemolysis was 5 or less for all groups which indi-cates no significant hemoglobin destruction whichsuggests that Mg-35Zn-3Ca alloy has no cytotoxicity

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Authorsrsquo Contribution

Il-Song Park contributed to this work and is considered asjoint first author

Acknowledgments

This work was supported by the National Research Founda-tion of Korea (NRF) Grant funded by the Korea government(MSIP) (no 2011-0028709 and no 2014R1A4A1005309) andRegional Strategic Industry project (2013-R0002274)

References

[1] D A Puleo and W W Huh ldquoAcute toxicity of metal ions incultures of osteogenic cells derived from bone marrow stromalcellsrdquo Journal of Applied Biomaterials vol 6 no 2 pp 109ndash1161995

[2] J J Jacobs J L Gilbert and R M Urban ldquoCurrent conceptsreview Corrosion of metal orthopaedic implantsrdquo The Journalof Bone amp Joint Surgery vol 80 pp 268ndash282 1998

[3] C Lhotka T Szekeres I Steffan K Zhuber and K ZweymullerldquoFour-year study of cobalt and chromium blood levels inpatients managed with two different metal-on-metal total hipreplacementsrdquo Journal of Orthopaedic Research vol 21 no 2pp 189ndash195 2003

[4] J J Jacobs A K Skipor L M Patterson et al ldquoMetal releasein patients who have had a primary total hip arthroplasty Aprospective controlled longitudinal studyrdquoThe Journal of Boneand Joint SurgerymdashAmerican Volume vol 80 no 10 pp 1447ndash1458 1998

[5] J J Jacobs N J Hallab A K Skipor and R M UrbanldquoMetal degradation products a cause for concern in metal-metal bearingsrdquo Clinical Orthopaedics and Related Researchno 417 pp 139ndash147 2003

[6] J Nagels M Stokdijk and P M Rozing ldquoStress shielding andbone resorption in shoulder arthroplastyrdquo Journal of Shoulderand Elbow Surgery vol 12 no 1 pp 35ndash39 2003

[7] H G Seiler H Sigel and A Sigel Handbook on Toxicity ofInorganic Compounds 1988

[8] M P Staiger A M Pietak J Huadmai and G Dias ldquoMag-nesium and its alloys as orthopedic biomaterials a reviewrdquoBiomaterials vol 27 no 9 pp 1728ndash1734 2006

[9] E P DeGarmo J T Black and R A Kohser DeGarmorsquosMaterials and Processes in Manufacturing John Wiley amp Sons2011

[10] L J Gibson and M F Ashby Cellular Solids Structure andProperties Cambridge University Press 1999

10 Advances in Materials Science and Engineering

[11] J-W Choi Y-M Kong H-E Kim and I-S Lee ldquoReinforce-ment of hydroxyapatite bioceramic by addition of Ni

3

Al andAl2

O3

rdquo Journal of the American Ceramic Society vol 81 no 7pp 1743ndash1748 1998

[12] T Thamaraiselvi and S Rajeswari ldquoBiological evaluation ofbioceramic materialsmdasha reviewrdquo Trends in Biomaterials andArtificial Organs vol 18 no 1 pp 9ndash17 2004

[13] H Zreiqat C R Howlett A Zannettino et al ldquoMechanismsof magnesium-stimulated adhesion of osteoblastic cells tocommonly used orthopaedic implantsrdquo Journal of BiomedicalMaterials Research vol 62 no 2 pp 175ndash184 2002

[14] F Witte V Kaese H Haferkamp et al ldquoIn vivo corrosionof four magnesium alloys and the associated bone responserdquoBiomaterials vol 26 no 17 pp 3557ndash3563 2005

[15] C EWenMMabuchi Y Yamada K Shimojima Y Chino andT Asahina ldquoProcessing of biocompatible porous Ti and MgrdquoScripta Materialia vol 45 no 10 pp 1147ndash1153 2001

[16] G Song ldquoRecent progress in corrosion and protection ofmagnesium alloysrdquo Advanced Engineering Materials vol 7 no7 pp 563ndash586 2005

[17] S S A El-Rahman ldquoNeuropathology of aluminum toxicityin rats (glutamate and GABA impairment)rdquo PharmacologicalResearch vol 47 no 3 pp 189ndash194 2003

[18] Y Nakamura Y Tsumura Y Tonogai T Shibata and Y ItoldquoDifferences in behavior among the chlorides of seven rare earthelements administered intravenously to ratsrdquo Toxicological Sci-ences vol 37 no 2 pp 106ndash116 1997

[19] J Z Ilich and J E Kerstetter ldquoNutrition in bone health revisiteda story beyond calciumrdquo Journal of the American College ofNutrition vol 19 no 6 pp 715ndash737 2000

[20] J C Oh T Ohkubo T Mukai and K Hono ldquoTEM and 3DAPcharacterization of an age-hardened Mg-Ca-Zn alloyrdquo ScriptaMaterialia vol 53 no 6 pp 675ndash679 2005

[21] G Levi S Avraham A Zilberov and M Bamberger ldquoSolidifi-cation solution treatment and age hardening of a Mg-16 wtCa-32 wt Zn alloyrdquo Acta Materialia vol 54 no 2 pp 523ndash530 2006

[22] T Miyazaki J Kaneko and M Sugamata ldquoStructures andproperties of rapidly solidified Mg-Ca based alloysrdquo MaterialsScience and Engineering A vol 181-182 pp 1410ndash1414 1994

[23] C Liu Y Xin G Tang and P K Chu ldquoInfluence of heattreatment on degradation behavior of bio-degradable die-castAZ63 magnesium alloy in simulated body fluidrdquo MaterialsScience and Engineering A vol 456 no 1-2 pp 350ndash357 2007

[24] X Gu Y Zheng Y Cheng S Zhong and T Xi ldquoIn vitrocorrosion and biocompatibility of binary magnesium alloysrdquoBiomaterials vol 30 no 4 pp 484ndash498 2009

[25] B A Shaw Corrosion Resistance of Magnesium Alloys vol 13ASM handbook 2003

[26] V Kaesel P T Tai F Bach H Haferkamp F Witte and HWindhagen ldquoApproach to control the corrosion of magnesiumby alloyingrdquo inMagnesium Proceedings of the 6th InternationalConference Magnesium Alloys and Their Applications pp 534ndash539 Wiley Online Library 2004

[27] J E Gray and B Luan ldquoProtective coatings on magnesium andits alloysmdasha critical reviewrdquo Journal of Alloys and Compoundsvol 336 no 1-2 pp 88ndash113 2002

[28] M-C Zhao M Liu G Song and A Atrens ldquoInfluence of the120573-phase morphology on the corrosion of the Mg alloy AZ91rdquoCorrosion Science vol 50 no 7 pp 1939ndash1953 2008

[29] N N Aung andW Zhou ldquoEffect of heat treatment on corrosionand electrochemical behaviour of AZ91D magnesium alloyrdquoJournal of Applied Electrochemistry vol 32 no 12 pp 1397ndash14012002

[30] G Song A L Bowles and D H StJohn ldquoCorrosion resistanceof aged die cast magnesium alloy AZ91DrdquoMaterials Science andEngineering A vol 366 no 1 pp 74ndash86 2004

[31] M Jonsson D Persson and R Gubner ldquoThe initial steps ofatmospheric corrosion on magnesium alloy AZ91Drdquo Journal ofthe Electrochemical Society vol 154 no 11 pp C684ndashC691 2007

[32] T Beldjoudi C Fiaud and L Robbiola ldquoInfluence of homog-enization and artificial aging heat treatments on corrosionbehavior of Mg-Al alloysrdquo Corrosion vol 49 no 9 pp 738ndash7451993

[33] O Lunder J E Lein T K Aune and K Nisancioglu ldquoRole ofMg17Al12 phase in the corrosion of Mg alloy AZ91rdquo Corrosionvol 45 no 9 pp 741ndash748 1989

[34] D L Piron The Electrochemistry of Corrosion University ofHouston Houston Tex USA 1991

[35] G Song A Atrens D Stjohn J Nairn and Y Li ldquoThe electro-chemical corrosion of pure magnesium in 1 N NaClrdquo CorrosionScience vol 39 no 5 pp 855ndash875 1997

[36] Z Li X Gu S Lou and Y Zheng ldquoThe development of binaryMg-Ca alloys for use as biodegradable materials within bonerdquoBiomaterials vol 29 no 10 pp 1329ndash1344 2008

[37] A E Coy F Viejo P Skeldon and G E Thompson ldquoSus-ceptibility of rare-earth-magnesium alloys to micro-galvaniccorrosionrdquo Corrosion Science vol 52 no 12 pp 3896ndash39062010

[38] G Song and A Atrens ldquoUnderstanding magnesiumcorrosionmdasha framework for improved alloy performancerdquoAdvanced Engineering Materials vol 5 no 12 pp 837ndash8582003

[39] A F Crawley and K S Milliken ldquoPrecipitate morphology andorientation relationships in an agedMg-9Al-1 Zn-03Mnalloyrdquo Acta Metallurgica vol 22 no 5 pp 557ndash562 1974

[40] S O Sowemimo-Coker ldquoRed blood cell hemolysis duringprocessingrdquoTransfusionMedicine Reviews vol 16 no 1 pp 46ndash60 2002

[41] ISO ldquoBiological evaluation of medical devicesmdashPart 4 selec-tion of tests for interactions with bloodrdquo Tech Rep ISO 10993-4 2002

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CeramicsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CompositesJournal of

NanoparticlesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Biomaterials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MetallurgyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

MaterialsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nano

materials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofNanomaterials

4 Advances in Materials Science and Engineering

(a)

100 200 300 400 500 600 700 800

Ca

Zn

MgLSecs 42

Zn

00

31

124

62

93

155

900

KCnt

Energy (keV)

(b)

Figure 1 SEM micrograph of as-cast Mg-35Zn-3Ca (a) and EDX spectrum results (b)

Table 3 Elemental composition of Mg-35Zn-3Ca alloy assessed byenergy dispersive X-ray analysis

Atomic Weight Ca 276 355Zn 1554 3263Mg Balance Balance

and Ca (355 wt) as the major elements (Table 3) suggest-ing that the alloy conforms to the chemical compositionrequirements of Mg-35Zn-3Ca alloy

The DSC trace of the as-cast Mg-35Zn-3Ca alloy speci-men is shown in Figure 2 The liquidus and solidus temper-atures are 36184∘C and 34011∘C respectively Based on thisresult the suitable temperature for solution heat treatment isset as 310∘C which is slightly lower than the solidus tempera-ture of the alloy Accordingly the as-cast Mg-35Zn-3Ca alloyis homogenized at 310∘C for 48 h and quenched in deionizedwater at room temperature to prevent any microsegregationand residual stress during precipitation (designated as AT0)Some of the specimens were subjected to artificial aging heattreatment at 170∘C for 25 50 75 and 100 h and designatedas AT1 AT2 AT3 and AT4 respectively

The SEM images of the surface microstructure of theheat-treated (AT0) and artificially aged (AT1 AT2 AT3 andAT4) Mg-35Zn-3Ca alloy specimens etched in Nital for 5 sare shown in Figure 3 Among all the specimens the AT2group exhibits the finest and most homogenous distributionof 120572 and 120573 phases It is also evident from Figure 3 thatwith increase in aging time the size of 120572 phase is increasedwith the disappearance of the boundary of 120573 phase resultingin a change in microstructure from a homogeneous to aninhomogeneous state The X-ray elemental mapping of MgZn and Ca along with the secondary electron image ofthe Mg-35Zn-3Ca alloy is shown in Figure 4 It is evidentthat the darker regions of the microstructure are mostlythe 120572-Mg matrix whereas the lighter regions are mainly the

240 260 280 300 320 340 360 380 400 420

00

02

34011

34556 36184

34973

Temperature (∘C)

minus02

minus04

minus06

minus08

Hea

t flow

(cal

(g s

))

Figure 2 DSC thermogram (heating curve) of as-cast Mg-35Zn-3Ca alloy

120573-phase precipitate which are relatively lower in Mg andlargely consist of zinc and calcium

The potentiodynamic polarization curves of heat-treated(AT0) and artificially aged (AT1 AT2 AT3 and AT4) Mg-35Zn-3Ca alloy specimens in HBSS are shown in Figure 5The119864corr and 119894corr values of all the specimens calculated usingTafel extrapolation method are compiled in Table 4 There isnot much variation in the 119864corr of all the specimens testedand all of them lie in the range of minus120 to minus129V versusAgAgClKCl (satrsquod) The 119894corr values of the specimens thatare heat-treated and artificially aged for different duration oftime (AT1 to AT4) are relatively higher than those subjectedonly for heat treatment (AT0) Among the heat treated andartificially aged samples (AT1 to AT4) specimens of the AT2group exhibit a lower 119894corr Based on the 119894corr values thecorrosion resistance of the Mg-35Zn-3Ca alloys specimenssubjected to only heat treatment (AT0) and heat treatmentfollowed by artificial aging for different duration of time (AT1to AT4) can be ranked as follows AT0 gt AT2 gt AT3 gt AT4 gtAT1

Advances in Materials Science and Engineering 5

(a) (b) (c)

(d) (e) (f)

(g) (h) (i)

(j) (k) (l)

(m) (n) (o)

Figure 3 Surface morphology of various heat treated Mg-35Zn-3Ca alloys (a) AT0 (times2000) (b) AT0 (times5000) (c) AT0 (times10000) (d) AT1(times2000) (e) AT1 (times5000) (f) AT1 (times10000) (g) AT2 (times2000) (h) AT2 (times5000) (i) AT2 (times10000) (j) AT3 (times2000) (k) AT3 (times5000) (l) AT3(times10000) (m) AT4 (times2000) (n) AT4 (times5000) and (o) AT4 (times10000)

6 Advances in Materials Science and Engineering

Table 4 Electrochemical corrosion parameters of Mg-35Zn-3Ca alloy in HBSS derived from the potentiodynamic polarization test usingTafel extrapolation method

GroupAT0 AT1 AT2 AT3 AT4

119864corr (V vs AgAgClKCl (satrsquod)) minus129 minus123 minus123 minus120 minus123119894corr (120583Acm

2) 1011 5091 3641 3751 4908

CaZn

Mg

Figure 4 Analysis of elemental composition on the surface by EDX mapping of Mg-35Zn-3Ca alloy

Pote

ntia

l (V

ver

sus A

gClK

Cl)

AT0AT1AT2

AT3AT4

minus11

minus12

minus13

minus141E minus 8 1E minus 7 1E minus 6 1E minus 5 1E minus 4 1E minus 3

Current density (Acm2)

Figure 5 Potentiodynamic polarization curve obtained in HBSSvarious heat treated Mg-35Zn-3Ca alloys

The change in pH of the HBSS in which the Mg-35Zn-3Ca alloys subjected to only heat treatment (AT0) and heattreatment followed by artificial aging for different durations(AT1 to AT4) are immersed measured for a duration of 72 his shown in Figure 6 In general all the specimens exhibita rapid increase in pH during the first 6 h beyond whichthe extent of increase in pH is decreased Beyond 48 h ofimmersion the pH of HBSS reached a stable value for all thespecimens studiedDuring the first 6 h of immersion theMg-35Zn-3Ca alloy specimens subjected to heat treatment alone(AT0) showed a rapid increase in pHwhen compared to thosesubjected to heat treatment followed by artificial aging fordifferent duration of time (AT1 to AT4) Among the AT1 toAT4 group specimens of the AT2 group showed a relativelyless increase in pH suggesting the lower extent of dissolutionof the Mg alloy

The corrosion rate of the Mg-35Zn-3Ca alloy specimenssubjected to only heat treatment (AT0) and heat treatmentfollowed by artificial aging for different duration of time (AT1to AT4) calculated using the loss in weight after immersionin HBSS at 37∘C for 5 days is shown in Figure 7 It is evident

Advances in Materials Science and Engineering 7

0 12 24 36 48 60 72

pH

Ageing time (hour)

7

8

9

10

11

AT0AT1AT2

AT3AT4

Figure 6 pH value as a function of immersion time

AT0 AT1 AT2 AT3 AT40

1

2

3

4

232

308308

373

Sample code

392

Cor

rosio

n ra

te (m

g(c

m2

day)

)

Figure 7 Corrosion rates of different heat treated Mg-35Zn-3Caalloys after immersion in HBSS for 5 days

that specimens subjected to heat treatment alone (AT0) showa higher corrosion rate (392mg(cm2 day)) when comparedto those subjected to heat treatment followed by artificialaging for different durations (AT1 to AT4) (ranging from232 to 373mg(cm2 day)) Among the AT1 to AT4 groupspecimens of the AT2 group showed a lower corrosion rate of232mg(cm2 day) which is significantly lower than those ofother groups (119875 lt 005)

In vitro hemolysis test is a well-known method to assessthe biotoxicity in a short duration of time The hemolysisability of Mg-35Zn-3Ca alloy specimens subjected to onlyheat treatment (AT0) and heat treatment followed by arti-ficial aging for different duration of time (AT1 to AT4) ismeasured using the positive (10mL saline solution containing01 wt of Na

2CO3) and negative (10mL saline solution)

as controls The measured optical density values and the

Table 5 Absorbance value measured at 540 nm and percentage ofhemolysis of Mg-35Zn-3Ca alloy subjected to heat treatment andartificial aging for different duration of time

Sample code OD at 540 nm Hemolysis ()AT0 0051 plusmn 0002 0515 plusmn 0375AT1 0050 plusmn 0002 0371 plusmn 0204AT2 0049 plusmn 0001 0147 plusmn 0104AT3 0050 plusmn 0001 0299 plusmn 0275AT4 0051 plusmn 0002 0521 plusmn 0272Negative 0049 plusmn 0001 0Positive 0495 plusmn 0013 100

hemolysis are compiled in Table 5 The variation in the hemolysis of all the samples tested alongwith the negative andpositive controls is plotted in Figure 8 for a better comparisonand to understand the statistical difference among themIt is evident from Table 5 and Figure 8 that among all thespecimens tested those belonging to the AT2 group showedthe lowest value of hemolysis (0147) However whencompared to other groups the difference in hemolysis isstatistically insignificant (119875 gt 005)

4 Discussion

Mg undergoes rapid corrosion in electrolytes containingchlorides such as body fluid Hence it will be difficult touse Mg for implant applications When Mg is exposed to airthe oxide layer formed on its surface offers only a partialprotection In aqueous solution the formation of porousMg(OH)

2layer could not offer much protection (equation

(3)) In presence of chloride ions it gets dissolved as MgCl2

while the aggressive nature of the medium causes severecorrosion of theMg (equations (4) and (5)) [25]The reactionsequences ofMg in aqueousmedium in the absence (equation(3)) and presence (equations (4) and (5)) of chloride ions canbe represented as follows [8]

Mg (solid) + 2H2O 997888rarr Mg (OH)

2+H2(gas) (3)

Mg (solid) + 2Clminus (aqueous) 997888rarr MgCl2

(4)

Mg (OH)2(solid) + 2Clminus 997888rarr MgCl

2 (5)

The corrosion resistance of Mg could be improvedthrough alloying formation of composites surface treat-ment and heat treatment [25ndash31] However the alloyingelements the second phase materials used to prepare thecomposites and the surface treated layer should not beharmful to the body when used as a biomaterial Someof the commonly used Mg-based alloys contain aluminumthat is harmful to the nervous system and osteoblasts whilethe RE-based Mg alloys could cause blood toxicity [1718] In the present study Mg-35Zn-3Ca alloy is preparedby adding zinc and calcium as alloying elements both ofwhich are nontoxic Alloying magnesium with zinc enablesprecipitation hardening while alloying with calcium couldhelp in grain refinement The microstructure and corrosion

8 Advances in Materials Science and Engineering

AT0 AT1 AT2 AT3 AT4 Negative Positive

0

1

2

90

100

05150371

01470299

0521

100

Hem

olys

is (

)

Sample code

0

Figure 8 Hemolysis percentage of various heat treated Mg-35Zn-3Ca alloys

resistance of the Mg-35Zn-3Ca alloy are evaluated aftersubjecting them to only heat treatment (AT0) and heattreatment and artificial aging for different duration of time(AT1 to AT4)

The microstructural examination after solution heattreatment and artificial aging heat treatment performed overa specific period of time showed that the 120572 and 120573 phaseswere finest and most homogenous in the AT2 group whichunderwent an artificial aging heat treatment at 170∘C for5 h Moreover the grain boundary was broken and 120573 phasewas inhomogeneous in the AT3 group which underwentartificial aging heat treatment for 75 h Results also showedthat the size of crystal grain became larger and the continuityof the crystal margin has disappeared in the AT4 groupwhich underwent artificial aging heat treatment for 10 h(Figure 3) Solution heat treatment is a process to preparethe supersaturated solid solution of unstable state materialsare generally softened by solution heat treatment Previousstudies have reported that artificial aging heat treatmentfollowing solution heat treatment of Mg alloy improvedstrength by refinement of the precipitate [29] Meanwhile itwas reported that heat treatment changed the microstruc-ture of alloy thereby affecting the corrosion behavior[32 33]

In this study potentiodynamic polarization studieschange in pH of HBSS and loss in weight after immersionin HBSS were used to assess the corrosion resistance of theMg-35Zn-3Ca alloy both in as-prepared and heat-treatedconditions The results of the potentiodynamic polarizationtest conducted to assess electrochemical corrosion behaviorshowed the lowest corrosion current density of 1011120583Acm2for the AT0 group which underwent only the solutionheat treatment Among the groups that underwent artificialaging following solution heat treatment the lowest corro-sion current density of 3641 120583Acm2 is observed for theAT2 group The corrosion current density which is closelyassociated with corrosion rate is an intersection point atwhich the negative Tafel slope is extrapolated to corrosionpotential by the Tafel extrapolation method [34] This resultshowed that corrosion resistance of the Mg-35Zn-3Ca alloy

is much improved for the group that underwent solution heattreatment alone than in groups that underwent artificial agingheat treatment following solution heat treatment Whenimmersed in HBSS Mg undergoes anodic dissolution withthe release of H

2gas and generation of OHminus ions resulting

in an increase in pH of the medium [35] These reactionsequences can be represented as follows [36]

Anodic reaction Mg 997888rarr Mg2+ + 2e (6)

Cathodic reaction 2H2O + 2e 997888rarr H

2+ 2OHminus (7)

Formation of corrosion product

Mg2+ + 2OHminus 997888rarr Mg (OH)2

(8)

Thus the rate of corrosion of MgMg alloys could beestimated from the change in pH of the corrosive medium(HBSS in this study) as a function of time The change inpH of the HBSS measured as a function of time (Figure 6)showed that it is slowest for specimens in the T2 group whencompared to other groups This inference indicates that thecorrosion resistance is increased as the microstructure ofthe surface gets finer and denser The loss in weight of thespecimens measured after 5 days of immersion in HBSS is232mg(cm2 day) for the AT2 group which is significantlylower than that of the other groups (119875 lt 005) The lossin weight is 392mg(cm2 day) for the AT0 group whichis the highest among all the specimens tested Howeverthe difference between the specimens is insignificant whencomparedwith the specimens in other groups except with theAT2 group (119875 gt 005) Hence it is clear that the specimens ofthe AT2 group have offered an excellent corrosion resistancewhich is consistent with the results of change in pHHoweverthe results are inconsistent with those of the potentiodynamicpolarization test The fineness and homogeneity of the 120573phase largely determine the corrosion behavior which isreflected in the pH variation and weight loss These resultssupported that corrosion behavior of magnesium alloyswith multiphase structure is changed according to corro-sion potential difference distribution and volume fractionbetween micr-constituent phases [16 37 38] Since thesemeasurements are made for a long term the ability of the120573 phase to act as a physical barrier for corrosion becomeseffective [33 39] However during the electrochemical studysince the test is performed over a short duration the effect isnot reflected [29]

The hemolysis test which is conducted to assess thetoxicity to the body uses the principle that red blood cellsare divided or necrotized when the hemoglobin is destroyedThe concentration of free hemoglobin is proportional to thenumber of the injured RBC and the volume of the fluid [2440] The results of hemolysis test showed that the percentageof hemolysis (0147) in AT2 group is the lowest among allthe samples tested and when compared with other groups nostatistical significance difference could be observed (Figure 8Table 5) (119875 gt 005) In general if the hemolysis value is 5or less then it is considered as nonhemolytic according to

Advances in Materials Science and Engineering 9

ISO 10993-42002 [41] Accordingly the composition of Mg-35Zn-3Ca has low hemolysis and analogies good biocompat-ibility In other words homogenization and aging process ofthe Mg-35Zn-3Ca alloy can improve the physical propertiesand corrosion resistance of the material and it does not havea significant effect on the hemolytic toxicity

5 Conclusions

The preparation of Mg-35Zn-3Ca alloy containing zinc andcalcium rather than aluminum or RE elements as nontoxicand biocompatible alloying elements followed by heat treat-ment and artificial aging of the alloy to control its rate ofdegradation is reported The study leads to the followingconclusions

(1) DSC studies showed that the liquidus and solidustemperatures of the Mg-35Zn-3Ca alloy were36184∘C and 34011∘C respectively

(2) The microstructural features of the Mg-35Zn-3Caalloy indicate the presence of 120572-Mg matrix and 120573phase after heat treatment and artificial aging forvarious duration of time Among them the AT2group (heat treatment at 170∘C for 5 h followed byartificial aging at 310∘C for 48 h) exhibits the finest andmost homogenous distribution of 120572 and 120573 phases

(3) Potentiodynamic polarization studies of the Mg-35Zn-3Ca alloy specimens indicate that the 119894corr valuesof specimens that are heat-treated and artificiallyaged for different duration of time (AT1 to AT4) arerelatively higher than those subjected only to heattreatment (AT0) Among heat-treated and artificiallyaged samples (AT1 to AT4) specimens of the AT2group exhibit a lower 119894corr Based on the 119894corr valuesthe specimens can be ranked as follows AT0 gtAT2 gtAT3 gt AT4 gt AT1

(4) The change in pH of theHBSSmeasured for 72 h indi-cates that all the specimens exhibit a rapid increase inpH during the first 6 h during which the Mg-35Zn-3Ca alloy specimens subjected to heat treatment alone(AT0) showed a rapid increase in pH Beyond 48 hof immersion the pH of HBSS reached a stable valuefor all the specimens studied Among the AT1 toAT4 groups specimens of the AT2 group showed arelatively less increase in pH suggesting the lowerextent of dissolution of the Mg alloy

(5) Mg-35Zn-3Ca alloy specimens subjected to heattreatment alone (AT0) showed a corrosion rate of392mg(cm2 day) than those subjected to heat treat-ment followed by artificial aging for different dura-tions (AT1 to AT4) which ranges between 232 and373mg(cm2 day) Among the AT1 to AT4 groupsspecimens of theAT2 group showed a lower corrosionrate of 232mg(cm2 day) which is significantly lowerthan those of other groups (119875 lt 005)

(6) In vitro hemolysis test showed the lowest hemolysispercentage value of 0147 for the AT2 group but

the differences were statistically insignificant whencompared with that of other groups (119875 lt 005) Thehemolysis was 5 or less for all groups which indi-cates no significant hemoglobin destruction whichsuggests that Mg-35Zn-3Ca alloy has no cytotoxicity

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Authorsrsquo Contribution

Il-Song Park contributed to this work and is considered asjoint first author

Acknowledgments

This work was supported by the National Research Founda-tion of Korea (NRF) Grant funded by the Korea government(MSIP) (no 2011-0028709 and no 2014R1A4A1005309) andRegional Strategic Industry project (2013-R0002274)

References

[1] D A Puleo and W W Huh ldquoAcute toxicity of metal ions incultures of osteogenic cells derived from bone marrow stromalcellsrdquo Journal of Applied Biomaterials vol 6 no 2 pp 109ndash1161995

[2] J J Jacobs J L Gilbert and R M Urban ldquoCurrent conceptsreview Corrosion of metal orthopaedic implantsrdquo The Journalof Bone amp Joint Surgery vol 80 pp 268ndash282 1998

[3] C Lhotka T Szekeres I Steffan K Zhuber and K ZweymullerldquoFour-year study of cobalt and chromium blood levels inpatients managed with two different metal-on-metal total hipreplacementsrdquo Journal of Orthopaedic Research vol 21 no 2pp 189ndash195 2003

[4] J J Jacobs A K Skipor L M Patterson et al ldquoMetal releasein patients who have had a primary total hip arthroplasty Aprospective controlled longitudinal studyrdquoThe Journal of Boneand Joint SurgerymdashAmerican Volume vol 80 no 10 pp 1447ndash1458 1998

[5] J J Jacobs N J Hallab A K Skipor and R M UrbanldquoMetal degradation products a cause for concern in metal-metal bearingsrdquo Clinical Orthopaedics and Related Researchno 417 pp 139ndash147 2003

[6] J Nagels M Stokdijk and P M Rozing ldquoStress shielding andbone resorption in shoulder arthroplastyrdquo Journal of Shoulderand Elbow Surgery vol 12 no 1 pp 35ndash39 2003

[7] H G Seiler H Sigel and A Sigel Handbook on Toxicity ofInorganic Compounds 1988

[8] M P Staiger A M Pietak J Huadmai and G Dias ldquoMag-nesium and its alloys as orthopedic biomaterials a reviewrdquoBiomaterials vol 27 no 9 pp 1728ndash1734 2006

[9] E P DeGarmo J T Black and R A Kohser DeGarmorsquosMaterials and Processes in Manufacturing John Wiley amp Sons2011

[10] L J Gibson and M F Ashby Cellular Solids Structure andProperties Cambridge University Press 1999

10 Advances in Materials Science and Engineering

[11] J-W Choi Y-M Kong H-E Kim and I-S Lee ldquoReinforce-ment of hydroxyapatite bioceramic by addition of Ni

3

Al andAl2

O3

rdquo Journal of the American Ceramic Society vol 81 no 7pp 1743ndash1748 1998

[12] T Thamaraiselvi and S Rajeswari ldquoBiological evaluation ofbioceramic materialsmdasha reviewrdquo Trends in Biomaterials andArtificial Organs vol 18 no 1 pp 9ndash17 2004

[13] H Zreiqat C R Howlett A Zannettino et al ldquoMechanismsof magnesium-stimulated adhesion of osteoblastic cells tocommonly used orthopaedic implantsrdquo Journal of BiomedicalMaterials Research vol 62 no 2 pp 175ndash184 2002

[14] F Witte V Kaese H Haferkamp et al ldquoIn vivo corrosionof four magnesium alloys and the associated bone responserdquoBiomaterials vol 26 no 17 pp 3557ndash3563 2005

[15] C EWenMMabuchi Y Yamada K Shimojima Y Chino andT Asahina ldquoProcessing of biocompatible porous Ti and MgrdquoScripta Materialia vol 45 no 10 pp 1147ndash1153 2001

[16] G Song ldquoRecent progress in corrosion and protection ofmagnesium alloysrdquo Advanced Engineering Materials vol 7 no7 pp 563ndash586 2005

[17] S S A El-Rahman ldquoNeuropathology of aluminum toxicityin rats (glutamate and GABA impairment)rdquo PharmacologicalResearch vol 47 no 3 pp 189ndash194 2003

[18] Y Nakamura Y Tsumura Y Tonogai T Shibata and Y ItoldquoDifferences in behavior among the chlorides of seven rare earthelements administered intravenously to ratsrdquo Toxicological Sci-ences vol 37 no 2 pp 106ndash116 1997

[19] J Z Ilich and J E Kerstetter ldquoNutrition in bone health revisiteda story beyond calciumrdquo Journal of the American College ofNutrition vol 19 no 6 pp 715ndash737 2000

[20] J C Oh T Ohkubo T Mukai and K Hono ldquoTEM and 3DAPcharacterization of an age-hardened Mg-Ca-Zn alloyrdquo ScriptaMaterialia vol 53 no 6 pp 675ndash679 2005

[21] G Levi S Avraham A Zilberov and M Bamberger ldquoSolidifi-cation solution treatment and age hardening of a Mg-16 wtCa-32 wt Zn alloyrdquo Acta Materialia vol 54 no 2 pp 523ndash530 2006

[22] T Miyazaki J Kaneko and M Sugamata ldquoStructures andproperties of rapidly solidified Mg-Ca based alloysrdquo MaterialsScience and Engineering A vol 181-182 pp 1410ndash1414 1994

[23] C Liu Y Xin G Tang and P K Chu ldquoInfluence of heattreatment on degradation behavior of bio-degradable die-castAZ63 magnesium alloy in simulated body fluidrdquo MaterialsScience and Engineering A vol 456 no 1-2 pp 350ndash357 2007

[24] X Gu Y Zheng Y Cheng S Zhong and T Xi ldquoIn vitrocorrosion and biocompatibility of binary magnesium alloysrdquoBiomaterials vol 30 no 4 pp 484ndash498 2009

[25] B A Shaw Corrosion Resistance of Magnesium Alloys vol 13ASM handbook 2003

[26] V Kaesel P T Tai F Bach H Haferkamp F Witte and HWindhagen ldquoApproach to control the corrosion of magnesiumby alloyingrdquo inMagnesium Proceedings of the 6th InternationalConference Magnesium Alloys and Their Applications pp 534ndash539 Wiley Online Library 2004

[27] J E Gray and B Luan ldquoProtective coatings on magnesium andits alloysmdasha critical reviewrdquo Journal of Alloys and Compoundsvol 336 no 1-2 pp 88ndash113 2002

[28] M-C Zhao M Liu G Song and A Atrens ldquoInfluence of the120573-phase morphology on the corrosion of the Mg alloy AZ91rdquoCorrosion Science vol 50 no 7 pp 1939ndash1953 2008

[29] N N Aung andW Zhou ldquoEffect of heat treatment on corrosionand electrochemical behaviour of AZ91D magnesium alloyrdquoJournal of Applied Electrochemistry vol 32 no 12 pp 1397ndash14012002

[30] G Song A L Bowles and D H StJohn ldquoCorrosion resistanceof aged die cast magnesium alloy AZ91DrdquoMaterials Science andEngineering A vol 366 no 1 pp 74ndash86 2004

[31] M Jonsson D Persson and R Gubner ldquoThe initial steps ofatmospheric corrosion on magnesium alloy AZ91Drdquo Journal ofthe Electrochemical Society vol 154 no 11 pp C684ndashC691 2007

[32] T Beldjoudi C Fiaud and L Robbiola ldquoInfluence of homog-enization and artificial aging heat treatments on corrosionbehavior of Mg-Al alloysrdquo Corrosion vol 49 no 9 pp 738ndash7451993

[33] O Lunder J E Lein T K Aune and K Nisancioglu ldquoRole ofMg17Al12 phase in the corrosion of Mg alloy AZ91rdquo Corrosionvol 45 no 9 pp 741ndash748 1989

[34] D L Piron The Electrochemistry of Corrosion University ofHouston Houston Tex USA 1991

[35] G Song A Atrens D Stjohn J Nairn and Y Li ldquoThe electro-chemical corrosion of pure magnesium in 1 N NaClrdquo CorrosionScience vol 39 no 5 pp 855ndash875 1997

[36] Z Li X Gu S Lou and Y Zheng ldquoThe development of binaryMg-Ca alloys for use as biodegradable materials within bonerdquoBiomaterials vol 29 no 10 pp 1329ndash1344 2008

[37] A E Coy F Viejo P Skeldon and G E Thompson ldquoSus-ceptibility of rare-earth-magnesium alloys to micro-galvaniccorrosionrdquo Corrosion Science vol 52 no 12 pp 3896ndash39062010

[38] G Song and A Atrens ldquoUnderstanding magnesiumcorrosionmdasha framework for improved alloy performancerdquoAdvanced Engineering Materials vol 5 no 12 pp 837ndash8582003

[39] A F Crawley and K S Milliken ldquoPrecipitate morphology andorientation relationships in an agedMg-9Al-1 Zn-03Mnalloyrdquo Acta Metallurgica vol 22 no 5 pp 557ndash562 1974

[40] S O Sowemimo-Coker ldquoRed blood cell hemolysis duringprocessingrdquoTransfusionMedicine Reviews vol 16 no 1 pp 46ndash60 2002

[41] ISO ldquoBiological evaluation of medical devicesmdashPart 4 selec-tion of tests for interactions with bloodrdquo Tech Rep ISO 10993-4 2002

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CeramicsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CompositesJournal of

NanoparticlesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Biomaterials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MetallurgyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

MaterialsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nano

materials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofNanomaterials

Advances in Materials Science and Engineering 5

(a) (b) (c)

(d) (e) (f)

(g) (h) (i)

(j) (k) (l)

(m) (n) (o)

Figure 3 Surface morphology of various heat treated Mg-35Zn-3Ca alloys (a) AT0 (times2000) (b) AT0 (times5000) (c) AT0 (times10000) (d) AT1(times2000) (e) AT1 (times5000) (f) AT1 (times10000) (g) AT2 (times2000) (h) AT2 (times5000) (i) AT2 (times10000) (j) AT3 (times2000) (k) AT3 (times5000) (l) AT3(times10000) (m) AT4 (times2000) (n) AT4 (times5000) and (o) AT4 (times10000)

6 Advances in Materials Science and Engineering

Table 4 Electrochemical corrosion parameters of Mg-35Zn-3Ca alloy in HBSS derived from the potentiodynamic polarization test usingTafel extrapolation method

GroupAT0 AT1 AT2 AT3 AT4

119864corr (V vs AgAgClKCl (satrsquod)) minus129 minus123 minus123 minus120 minus123119894corr (120583Acm

2) 1011 5091 3641 3751 4908

CaZn

Mg

Figure 4 Analysis of elemental composition on the surface by EDX mapping of Mg-35Zn-3Ca alloy

Pote

ntia

l (V

ver

sus A

gClK

Cl)

AT0AT1AT2

AT3AT4

minus11

minus12

minus13

minus141E minus 8 1E minus 7 1E minus 6 1E minus 5 1E minus 4 1E minus 3

Current density (Acm2)

Figure 5 Potentiodynamic polarization curve obtained in HBSSvarious heat treated Mg-35Zn-3Ca alloys

The change in pH of the HBSS in which the Mg-35Zn-3Ca alloys subjected to only heat treatment (AT0) and heattreatment followed by artificial aging for different durations(AT1 to AT4) are immersed measured for a duration of 72 his shown in Figure 6 In general all the specimens exhibita rapid increase in pH during the first 6 h beyond whichthe extent of increase in pH is decreased Beyond 48 h ofimmersion the pH of HBSS reached a stable value for all thespecimens studiedDuring the first 6 h of immersion theMg-35Zn-3Ca alloy specimens subjected to heat treatment alone(AT0) showed a rapid increase in pHwhen compared to thosesubjected to heat treatment followed by artificial aging fordifferent duration of time (AT1 to AT4) Among the AT1 toAT4 group specimens of the AT2 group showed a relativelyless increase in pH suggesting the lower extent of dissolutionof the Mg alloy

The corrosion rate of the Mg-35Zn-3Ca alloy specimenssubjected to only heat treatment (AT0) and heat treatmentfollowed by artificial aging for different duration of time (AT1to AT4) calculated using the loss in weight after immersionin HBSS at 37∘C for 5 days is shown in Figure 7 It is evident

Advances in Materials Science and Engineering 7

0 12 24 36 48 60 72

pH

Ageing time (hour)

7

8

9

10

11

AT0AT1AT2

AT3AT4

Figure 6 pH value as a function of immersion time

AT0 AT1 AT2 AT3 AT40

1

2

3

4

232

308308

373

Sample code

392

Cor

rosio

n ra

te (m

g(c

m2

day)

)

Figure 7 Corrosion rates of different heat treated Mg-35Zn-3Caalloys after immersion in HBSS for 5 days

that specimens subjected to heat treatment alone (AT0) showa higher corrosion rate (392mg(cm2 day)) when comparedto those subjected to heat treatment followed by artificialaging for different durations (AT1 to AT4) (ranging from232 to 373mg(cm2 day)) Among the AT1 to AT4 groupspecimens of the AT2 group showed a lower corrosion rate of232mg(cm2 day) which is significantly lower than those ofother groups (119875 lt 005)

In vitro hemolysis test is a well-known method to assessthe biotoxicity in a short duration of time The hemolysisability of Mg-35Zn-3Ca alloy specimens subjected to onlyheat treatment (AT0) and heat treatment followed by arti-ficial aging for different duration of time (AT1 to AT4) ismeasured using the positive (10mL saline solution containing01 wt of Na

2CO3) and negative (10mL saline solution)

as controls The measured optical density values and the

Table 5 Absorbance value measured at 540 nm and percentage ofhemolysis of Mg-35Zn-3Ca alloy subjected to heat treatment andartificial aging for different duration of time

Sample code OD at 540 nm Hemolysis ()AT0 0051 plusmn 0002 0515 plusmn 0375AT1 0050 plusmn 0002 0371 plusmn 0204AT2 0049 plusmn 0001 0147 plusmn 0104AT3 0050 plusmn 0001 0299 plusmn 0275AT4 0051 plusmn 0002 0521 plusmn 0272Negative 0049 plusmn 0001 0Positive 0495 plusmn 0013 100

hemolysis are compiled in Table 5 The variation in the hemolysis of all the samples tested alongwith the negative andpositive controls is plotted in Figure 8 for a better comparisonand to understand the statistical difference among themIt is evident from Table 5 and Figure 8 that among all thespecimens tested those belonging to the AT2 group showedthe lowest value of hemolysis (0147) However whencompared to other groups the difference in hemolysis isstatistically insignificant (119875 gt 005)

4 Discussion

Mg undergoes rapid corrosion in electrolytes containingchlorides such as body fluid Hence it will be difficult touse Mg for implant applications When Mg is exposed to airthe oxide layer formed on its surface offers only a partialprotection In aqueous solution the formation of porousMg(OH)

2layer could not offer much protection (equation

(3)) In presence of chloride ions it gets dissolved as MgCl2

while the aggressive nature of the medium causes severecorrosion of theMg (equations (4) and (5)) [25]The reactionsequences ofMg in aqueousmedium in the absence (equation(3)) and presence (equations (4) and (5)) of chloride ions canbe represented as follows [8]

Mg (solid) + 2H2O 997888rarr Mg (OH)

2+H2(gas) (3)

Mg (solid) + 2Clminus (aqueous) 997888rarr MgCl2

(4)

Mg (OH)2(solid) + 2Clminus 997888rarr MgCl

2 (5)

The corrosion resistance of Mg could be improvedthrough alloying formation of composites surface treat-ment and heat treatment [25ndash31] However the alloyingelements the second phase materials used to prepare thecomposites and the surface treated layer should not beharmful to the body when used as a biomaterial Someof the commonly used Mg-based alloys contain aluminumthat is harmful to the nervous system and osteoblasts whilethe RE-based Mg alloys could cause blood toxicity [1718] In the present study Mg-35Zn-3Ca alloy is preparedby adding zinc and calcium as alloying elements both ofwhich are nontoxic Alloying magnesium with zinc enablesprecipitation hardening while alloying with calcium couldhelp in grain refinement The microstructure and corrosion

8 Advances in Materials Science and Engineering

AT0 AT1 AT2 AT3 AT4 Negative Positive

0

1

2

90

100

05150371

01470299

0521

100

Hem

olys

is (

)

Sample code

0

Figure 8 Hemolysis percentage of various heat treated Mg-35Zn-3Ca alloys

resistance of the Mg-35Zn-3Ca alloy are evaluated aftersubjecting them to only heat treatment (AT0) and heattreatment and artificial aging for different duration of time(AT1 to AT4)

The microstructural examination after solution heattreatment and artificial aging heat treatment performed overa specific period of time showed that the 120572 and 120573 phaseswere finest and most homogenous in the AT2 group whichunderwent an artificial aging heat treatment at 170∘C for5 h Moreover the grain boundary was broken and 120573 phasewas inhomogeneous in the AT3 group which underwentartificial aging heat treatment for 75 h Results also showedthat the size of crystal grain became larger and the continuityof the crystal margin has disappeared in the AT4 groupwhich underwent artificial aging heat treatment for 10 h(Figure 3) Solution heat treatment is a process to preparethe supersaturated solid solution of unstable state materialsare generally softened by solution heat treatment Previousstudies have reported that artificial aging heat treatmentfollowing solution heat treatment of Mg alloy improvedstrength by refinement of the precipitate [29] Meanwhile itwas reported that heat treatment changed the microstruc-ture of alloy thereby affecting the corrosion behavior[32 33]

In this study potentiodynamic polarization studieschange in pH of HBSS and loss in weight after immersionin HBSS were used to assess the corrosion resistance of theMg-35Zn-3Ca alloy both in as-prepared and heat-treatedconditions The results of the potentiodynamic polarizationtest conducted to assess electrochemical corrosion behaviorshowed the lowest corrosion current density of 1011120583Acm2for the AT0 group which underwent only the solutionheat treatment Among the groups that underwent artificialaging following solution heat treatment the lowest corro-sion current density of 3641 120583Acm2 is observed for theAT2 group The corrosion current density which is closelyassociated with corrosion rate is an intersection point atwhich the negative Tafel slope is extrapolated to corrosionpotential by the Tafel extrapolation method [34] This resultshowed that corrosion resistance of the Mg-35Zn-3Ca alloy

is much improved for the group that underwent solution heattreatment alone than in groups that underwent artificial agingheat treatment following solution heat treatment Whenimmersed in HBSS Mg undergoes anodic dissolution withthe release of H

2gas and generation of OHminus ions resulting

in an increase in pH of the medium [35] These reactionsequences can be represented as follows [36]

Anodic reaction Mg 997888rarr Mg2+ + 2e (6)

Cathodic reaction 2H2O + 2e 997888rarr H

2+ 2OHminus (7)

Formation of corrosion product

Mg2+ + 2OHminus 997888rarr Mg (OH)2

(8)

Thus the rate of corrosion of MgMg alloys could beestimated from the change in pH of the corrosive medium(HBSS in this study) as a function of time The change inpH of the HBSS measured as a function of time (Figure 6)showed that it is slowest for specimens in the T2 group whencompared to other groups This inference indicates that thecorrosion resistance is increased as the microstructure ofthe surface gets finer and denser The loss in weight of thespecimens measured after 5 days of immersion in HBSS is232mg(cm2 day) for the AT2 group which is significantlylower than that of the other groups (119875 lt 005) The lossin weight is 392mg(cm2 day) for the AT0 group whichis the highest among all the specimens tested Howeverthe difference between the specimens is insignificant whencomparedwith the specimens in other groups except with theAT2 group (119875 gt 005) Hence it is clear that the specimens ofthe AT2 group have offered an excellent corrosion resistancewhich is consistent with the results of change in pHHoweverthe results are inconsistent with those of the potentiodynamicpolarization test The fineness and homogeneity of the 120573phase largely determine the corrosion behavior which isreflected in the pH variation and weight loss These resultssupported that corrosion behavior of magnesium alloyswith multiphase structure is changed according to corro-sion potential difference distribution and volume fractionbetween micr-constituent phases [16 37 38] Since thesemeasurements are made for a long term the ability of the120573 phase to act as a physical barrier for corrosion becomeseffective [33 39] However during the electrochemical studysince the test is performed over a short duration the effect isnot reflected [29]

The hemolysis test which is conducted to assess thetoxicity to the body uses the principle that red blood cellsare divided or necrotized when the hemoglobin is destroyedThe concentration of free hemoglobin is proportional to thenumber of the injured RBC and the volume of the fluid [2440] The results of hemolysis test showed that the percentageof hemolysis (0147) in AT2 group is the lowest among allthe samples tested and when compared with other groups nostatistical significance difference could be observed (Figure 8Table 5) (119875 gt 005) In general if the hemolysis value is 5or less then it is considered as nonhemolytic according to

Advances in Materials Science and Engineering 9

ISO 10993-42002 [41] Accordingly the composition of Mg-35Zn-3Ca has low hemolysis and analogies good biocompat-ibility In other words homogenization and aging process ofthe Mg-35Zn-3Ca alloy can improve the physical propertiesand corrosion resistance of the material and it does not havea significant effect on the hemolytic toxicity

5 Conclusions

The preparation of Mg-35Zn-3Ca alloy containing zinc andcalcium rather than aluminum or RE elements as nontoxicand biocompatible alloying elements followed by heat treat-ment and artificial aging of the alloy to control its rate ofdegradation is reported The study leads to the followingconclusions

(1) DSC studies showed that the liquidus and solidustemperatures of the Mg-35Zn-3Ca alloy were36184∘C and 34011∘C respectively

(2) The microstructural features of the Mg-35Zn-3Caalloy indicate the presence of 120572-Mg matrix and 120573phase after heat treatment and artificial aging forvarious duration of time Among them the AT2group (heat treatment at 170∘C for 5 h followed byartificial aging at 310∘C for 48 h) exhibits the finest andmost homogenous distribution of 120572 and 120573 phases

(3) Potentiodynamic polarization studies of the Mg-35Zn-3Ca alloy specimens indicate that the 119894corr valuesof specimens that are heat-treated and artificiallyaged for different duration of time (AT1 to AT4) arerelatively higher than those subjected only to heattreatment (AT0) Among heat-treated and artificiallyaged samples (AT1 to AT4) specimens of the AT2group exhibit a lower 119894corr Based on the 119894corr valuesthe specimens can be ranked as follows AT0 gtAT2 gtAT3 gt AT4 gt AT1

(4) The change in pH of theHBSSmeasured for 72 h indi-cates that all the specimens exhibit a rapid increase inpH during the first 6 h during which the Mg-35Zn-3Ca alloy specimens subjected to heat treatment alone(AT0) showed a rapid increase in pH Beyond 48 hof immersion the pH of HBSS reached a stable valuefor all the specimens studied Among the AT1 toAT4 groups specimens of the AT2 group showed arelatively less increase in pH suggesting the lowerextent of dissolution of the Mg alloy

(5) Mg-35Zn-3Ca alloy specimens subjected to heattreatment alone (AT0) showed a corrosion rate of392mg(cm2 day) than those subjected to heat treat-ment followed by artificial aging for different dura-tions (AT1 to AT4) which ranges between 232 and373mg(cm2 day) Among the AT1 to AT4 groupsspecimens of theAT2 group showed a lower corrosionrate of 232mg(cm2 day) which is significantly lowerthan those of other groups (119875 lt 005)

(6) In vitro hemolysis test showed the lowest hemolysispercentage value of 0147 for the AT2 group but

the differences were statistically insignificant whencompared with that of other groups (119875 lt 005) Thehemolysis was 5 or less for all groups which indi-cates no significant hemoglobin destruction whichsuggests that Mg-35Zn-3Ca alloy has no cytotoxicity

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Authorsrsquo Contribution

Il-Song Park contributed to this work and is considered asjoint first author

Acknowledgments

This work was supported by the National Research Founda-tion of Korea (NRF) Grant funded by the Korea government(MSIP) (no 2011-0028709 and no 2014R1A4A1005309) andRegional Strategic Industry project (2013-R0002274)

References

[1] D A Puleo and W W Huh ldquoAcute toxicity of metal ions incultures of osteogenic cells derived from bone marrow stromalcellsrdquo Journal of Applied Biomaterials vol 6 no 2 pp 109ndash1161995

[2] J J Jacobs J L Gilbert and R M Urban ldquoCurrent conceptsreview Corrosion of metal orthopaedic implantsrdquo The Journalof Bone amp Joint Surgery vol 80 pp 268ndash282 1998

[3] C Lhotka T Szekeres I Steffan K Zhuber and K ZweymullerldquoFour-year study of cobalt and chromium blood levels inpatients managed with two different metal-on-metal total hipreplacementsrdquo Journal of Orthopaedic Research vol 21 no 2pp 189ndash195 2003

[4] J J Jacobs A K Skipor L M Patterson et al ldquoMetal releasein patients who have had a primary total hip arthroplasty Aprospective controlled longitudinal studyrdquoThe Journal of Boneand Joint SurgerymdashAmerican Volume vol 80 no 10 pp 1447ndash1458 1998

[5] J J Jacobs N J Hallab A K Skipor and R M UrbanldquoMetal degradation products a cause for concern in metal-metal bearingsrdquo Clinical Orthopaedics and Related Researchno 417 pp 139ndash147 2003

[6] J Nagels M Stokdijk and P M Rozing ldquoStress shielding andbone resorption in shoulder arthroplastyrdquo Journal of Shoulderand Elbow Surgery vol 12 no 1 pp 35ndash39 2003

[7] H G Seiler H Sigel and A Sigel Handbook on Toxicity ofInorganic Compounds 1988

[8] M P Staiger A M Pietak J Huadmai and G Dias ldquoMag-nesium and its alloys as orthopedic biomaterials a reviewrdquoBiomaterials vol 27 no 9 pp 1728ndash1734 2006

[9] E P DeGarmo J T Black and R A Kohser DeGarmorsquosMaterials and Processes in Manufacturing John Wiley amp Sons2011

[10] L J Gibson and M F Ashby Cellular Solids Structure andProperties Cambridge University Press 1999

10 Advances in Materials Science and Engineering

[11] J-W Choi Y-M Kong H-E Kim and I-S Lee ldquoReinforce-ment of hydroxyapatite bioceramic by addition of Ni

3

Al andAl2

O3

rdquo Journal of the American Ceramic Society vol 81 no 7pp 1743ndash1748 1998

[12] T Thamaraiselvi and S Rajeswari ldquoBiological evaluation ofbioceramic materialsmdasha reviewrdquo Trends in Biomaterials andArtificial Organs vol 18 no 1 pp 9ndash17 2004

[13] H Zreiqat C R Howlett A Zannettino et al ldquoMechanismsof magnesium-stimulated adhesion of osteoblastic cells tocommonly used orthopaedic implantsrdquo Journal of BiomedicalMaterials Research vol 62 no 2 pp 175ndash184 2002

[14] F Witte V Kaese H Haferkamp et al ldquoIn vivo corrosionof four magnesium alloys and the associated bone responserdquoBiomaterials vol 26 no 17 pp 3557ndash3563 2005

[15] C EWenMMabuchi Y Yamada K Shimojima Y Chino andT Asahina ldquoProcessing of biocompatible porous Ti and MgrdquoScripta Materialia vol 45 no 10 pp 1147ndash1153 2001

[16] G Song ldquoRecent progress in corrosion and protection ofmagnesium alloysrdquo Advanced Engineering Materials vol 7 no7 pp 563ndash586 2005

[17] S S A El-Rahman ldquoNeuropathology of aluminum toxicityin rats (glutamate and GABA impairment)rdquo PharmacologicalResearch vol 47 no 3 pp 189ndash194 2003

[18] Y Nakamura Y Tsumura Y Tonogai T Shibata and Y ItoldquoDifferences in behavior among the chlorides of seven rare earthelements administered intravenously to ratsrdquo Toxicological Sci-ences vol 37 no 2 pp 106ndash116 1997

[19] J Z Ilich and J E Kerstetter ldquoNutrition in bone health revisiteda story beyond calciumrdquo Journal of the American College ofNutrition vol 19 no 6 pp 715ndash737 2000

[20] J C Oh T Ohkubo T Mukai and K Hono ldquoTEM and 3DAPcharacterization of an age-hardened Mg-Ca-Zn alloyrdquo ScriptaMaterialia vol 53 no 6 pp 675ndash679 2005

[21] G Levi S Avraham A Zilberov and M Bamberger ldquoSolidifi-cation solution treatment and age hardening of a Mg-16 wtCa-32 wt Zn alloyrdquo Acta Materialia vol 54 no 2 pp 523ndash530 2006

[22] T Miyazaki J Kaneko and M Sugamata ldquoStructures andproperties of rapidly solidified Mg-Ca based alloysrdquo MaterialsScience and Engineering A vol 181-182 pp 1410ndash1414 1994

[23] C Liu Y Xin G Tang and P K Chu ldquoInfluence of heattreatment on degradation behavior of bio-degradable die-castAZ63 magnesium alloy in simulated body fluidrdquo MaterialsScience and Engineering A vol 456 no 1-2 pp 350ndash357 2007

[24] X Gu Y Zheng Y Cheng S Zhong and T Xi ldquoIn vitrocorrosion and biocompatibility of binary magnesium alloysrdquoBiomaterials vol 30 no 4 pp 484ndash498 2009

[25] B A Shaw Corrosion Resistance of Magnesium Alloys vol 13ASM handbook 2003

[26] V Kaesel P T Tai F Bach H Haferkamp F Witte and HWindhagen ldquoApproach to control the corrosion of magnesiumby alloyingrdquo inMagnesium Proceedings of the 6th InternationalConference Magnesium Alloys and Their Applications pp 534ndash539 Wiley Online Library 2004

[27] J E Gray and B Luan ldquoProtective coatings on magnesium andits alloysmdasha critical reviewrdquo Journal of Alloys and Compoundsvol 336 no 1-2 pp 88ndash113 2002

[28] M-C Zhao M Liu G Song and A Atrens ldquoInfluence of the120573-phase morphology on the corrosion of the Mg alloy AZ91rdquoCorrosion Science vol 50 no 7 pp 1939ndash1953 2008

[29] N N Aung andW Zhou ldquoEffect of heat treatment on corrosionand electrochemical behaviour of AZ91D magnesium alloyrdquoJournal of Applied Electrochemistry vol 32 no 12 pp 1397ndash14012002

[30] G Song A L Bowles and D H StJohn ldquoCorrosion resistanceof aged die cast magnesium alloy AZ91DrdquoMaterials Science andEngineering A vol 366 no 1 pp 74ndash86 2004

[31] M Jonsson D Persson and R Gubner ldquoThe initial steps ofatmospheric corrosion on magnesium alloy AZ91Drdquo Journal ofthe Electrochemical Society vol 154 no 11 pp C684ndashC691 2007

[32] T Beldjoudi C Fiaud and L Robbiola ldquoInfluence of homog-enization and artificial aging heat treatments on corrosionbehavior of Mg-Al alloysrdquo Corrosion vol 49 no 9 pp 738ndash7451993

[33] O Lunder J E Lein T K Aune and K Nisancioglu ldquoRole ofMg17Al12 phase in the corrosion of Mg alloy AZ91rdquo Corrosionvol 45 no 9 pp 741ndash748 1989

[34] D L Piron The Electrochemistry of Corrosion University ofHouston Houston Tex USA 1991

[35] G Song A Atrens D Stjohn J Nairn and Y Li ldquoThe electro-chemical corrosion of pure magnesium in 1 N NaClrdquo CorrosionScience vol 39 no 5 pp 855ndash875 1997

[36] Z Li X Gu S Lou and Y Zheng ldquoThe development of binaryMg-Ca alloys for use as biodegradable materials within bonerdquoBiomaterials vol 29 no 10 pp 1329ndash1344 2008

[37] A E Coy F Viejo P Skeldon and G E Thompson ldquoSus-ceptibility of rare-earth-magnesium alloys to micro-galvaniccorrosionrdquo Corrosion Science vol 52 no 12 pp 3896ndash39062010

[38] G Song and A Atrens ldquoUnderstanding magnesiumcorrosionmdasha framework for improved alloy performancerdquoAdvanced Engineering Materials vol 5 no 12 pp 837ndash8582003

[39] A F Crawley and K S Milliken ldquoPrecipitate morphology andorientation relationships in an agedMg-9Al-1 Zn-03Mnalloyrdquo Acta Metallurgica vol 22 no 5 pp 557ndash562 1974

[40] S O Sowemimo-Coker ldquoRed blood cell hemolysis duringprocessingrdquoTransfusionMedicine Reviews vol 16 no 1 pp 46ndash60 2002

[41] ISO ldquoBiological evaluation of medical devicesmdashPart 4 selec-tion of tests for interactions with bloodrdquo Tech Rep ISO 10993-4 2002

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CeramicsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CompositesJournal of

NanoparticlesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Biomaterials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MetallurgyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

MaterialsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nano

materials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofNanomaterials

6 Advances in Materials Science and Engineering

Table 4 Electrochemical corrosion parameters of Mg-35Zn-3Ca alloy in HBSS derived from the potentiodynamic polarization test usingTafel extrapolation method

GroupAT0 AT1 AT2 AT3 AT4

119864corr (V vs AgAgClKCl (satrsquod)) minus129 minus123 minus123 minus120 minus123119894corr (120583Acm

2) 1011 5091 3641 3751 4908

CaZn

Mg

Figure 4 Analysis of elemental composition on the surface by EDX mapping of Mg-35Zn-3Ca alloy

Pote

ntia

l (V

ver

sus A

gClK

Cl)

AT0AT1AT2

AT3AT4

minus11

minus12

minus13

minus141E minus 8 1E minus 7 1E minus 6 1E minus 5 1E minus 4 1E minus 3

Current density (Acm2)

Figure 5 Potentiodynamic polarization curve obtained in HBSSvarious heat treated Mg-35Zn-3Ca alloys

The change in pH of the HBSS in which the Mg-35Zn-3Ca alloys subjected to only heat treatment (AT0) and heattreatment followed by artificial aging for different durations(AT1 to AT4) are immersed measured for a duration of 72 his shown in Figure 6 In general all the specimens exhibita rapid increase in pH during the first 6 h beyond whichthe extent of increase in pH is decreased Beyond 48 h ofimmersion the pH of HBSS reached a stable value for all thespecimens studiedDuring the first 6 h of immersion theMg-35Zn-3Ca alloy specimens subjected to heat treatment alone(AT0) showed a rapid increase in pHwhen compared to thosesubjected to heat treatment followed by artificial aging fordifferent duration of time (AT1 to AT4) Among the AT1 toAT4 group specimens of the AT2 group showed a relativelyless increase in pH suggesting the lower extent of dissolutionof the Mg alloy

The corrosion rate of the Mg-35Zn-3Ca alloy specimenssubjected to only heat treatment (AT0) and heat treatmentfollowed by artificial aging for different duration of time (AT1to AT4) calculated using the loss in weight after immersionin HBSS at 37∘C for 5 days is shown in Figure 7 It is evident

Advances in Materials Science and Engineering 7

0 12 24 36 48 60 72

pH

Ageing time (hour)

7

8

9

10

11

AT0AT1AT2

AT3AT4

Figure 6 pH value as a function of immersion time

AT0 AT1 AT2 AT3 AT40

1

2

3

4

232

308308

373

Sample code

392

Cor

rosio

n ra

te (m

g(c

m2

day)

)

Figure 7 Corrosion rates of different heat treated Mg-35Zn-3Caalloys after immersion in HBSS for 5 days

that specimens subjected to heat treatment alone (AT0) showa higher corrosion rate (392mg(cm2 day)) when comparedto those subjected to heat treatment followed by artificialaging for different durations (AT1 to AT4) (ranging from232 to 373mg(cm2 day)) Among the AT1 to AT4 groupspecimens of the AT2 group showed a lower corrosion rate of232mg(cm2 day) which is significantly lower than those ofother groups (119875 lt 005)

In vitro hemolysis test is a well-known method to assessthe biotoxicity in a short duration of time The hemolysisability of Mg-35Zn-3Ca alloy specimens subjected to onlyheat treatment (AT0) and heat treatment followed by arti-ficial aging for different duration of time (AT1 to AT4) ismeasured using the positive (10mL saline solution containing01 wt of Na

2CO3) and negative (10mL saline solution)

as controls The measured optical density values and the

Table 5 Absorbance value measured at 540 nm and percentage ofhemolysis of Mg-35Zn-3Ca alloy subjected to heat treatment andartificial aging for different duration of time

Sample code OD at 540 nm Hemolysis ()AT0 0051 plusmn 0002 0515 plusmn 0375AT1 0050 plusmn 0002 0371 plusmn 0204AT2 0049 plusmn 0001 0147 plusmn 0104AT3 0050 plusmn 0001 0299 plusmn 0275AT4 0051 plusmn 0002 0521 plusmn 0272Negative 0049 plusmn 0001 0Positive 0495 plusmn 0013 100

hemolysis are compiled in Table 5 The variation in the hemolysis of all the samples tested alongwith the negative andpositive controls is plotted in Figure 8 for a better comparisonand to understand the statistical difference among themIt is evident from Table 5 and Figure 8 that among all thespecimens tested those belonging to the AT2 group showedthe lowest value of hemolysis (0147) However whencompared to other groups the difference in hemolysis isstatistically insignificant (119875 gt 005)

4 Discussion

Mg undergoes rapid corrosion in electrolytes containingchlorides such as body fluid Hence it will be difficult touse Mg for implant applications When Mg is exposed to airthe oxide layer formed on its surface offers only a partialprotection In aqueous solution the formation of porousMg(OH)

2layer could not offer much protection (equation

(3)) In presence of chloride ions it gets dissolved as MgCl2

while the aggressive nature of the medium causes severecorrosion of theMg (equations (4) and (5)) [25]The reactionsequences ofMg in aqueousmedium in the absence (equation(3)) and presence (equations (4) and (5)) of chloride ions canbe represented as follows [8]

Mg (solid) + 2H2O 997888rarr Mg (OH)

2+H2(gas) (3)

Mg (solid) + 2Clminus (aqueous) 997888rarr MgCl2

(4)

Mg (OH)2(solid) + 2Clminus 997888rarr MgCl

2 (5)

The corrosion resistance of Mg could be improvedthrough alloying formation of composites surface treat-ment and heat treatment [25ndash31] However the alloyingelements the second phase materials used to prepare thecomposites and the surface treated layer should not beharmful to the body when used as a biomaterial Someof the commonly used Mg-based alloys contain aluminumthat is harmful to the nervous system and osteoblasts whilethe RE-based Mg alloys could cause blood toxicity [1718] In the present study Mg-35Zn-3Ca alloy is preparedby adding zinc and calcium as alloying elements both ofwhich are nontoxic Alloying magnesium with zinc enablesprecipitation hardening while alloying with calcium couldhelp in grain refinement The microstructure and corrosion

8 Advances in Materials Science and Engineering

AT0 AT1 AT2 AT3 AT4 Negative Positive

0

1

2

90

100

05150371

01470299

0521

100

Hem

olys

is (

)

Sample code

0

Figure 8 Hemolysis percentage of various heat treated Mg-35Zn-3Ca alloys

resistance of the Mg-35Zn-3Ca alloy are evaluated aftersubjecting them to only heat treatment (AT0) and heattreatment and artificial aging for different duration of time(AT1 to AT4)

The microstructural examination after solution heattreatment and artificial aging heat treatment performed overa specific period of time showed that the 120572 and 120573 phaseswere finest and most homogenous in the AT2 group whichunderwent an artificial aging heat treatment at 170∘C for5 h Moreover the grain boundary was broken and 120573 phasewas inhomogeneous in the AT3 group which underwentartificial aging heat treatment for 75 h Results also showedthat the size of crystal grain became larger and the continuityof the crystal margin has disappeared in the AT4 groupwhich underwent artificial aging heat treatment for 10 h(Figure 3) Solution heat treatment is a process to preparethe supersaturated solid solution of unstable state materialsare generally softened by solution heat treatment Previousstudies have reported that artificial aging heat treatmentfollowing solution heat treatment of Mg alloy improvedstrength by refinement of the precipitate [29] Meanwhile itwas reported that heat treatment changed the microstruc-ture of alloy thereby affecting the corrosion behavior[32 33]

In this study potentiodynamic polarization studieschange in pH of HBSS and loss in weight after immersionin HBSS were used to assess the corrosion resistance of theMg-35Zn-3Ca alloy both in as-prepared and heat-treatedconditions The results of the potentiodynamic polarizationtest conducted to assess electrochemical corrosion behaviorshowed the lowest corrosion current density of 1011120583Acm2for the AT0 group which underwent only the solutionheat treatment Among the groups that underwent artificialaging following solution heat treatment the lowest corro-sion current density of 3641 120583Acm2 is observed for theAT2 group The corrosion current density which is closelyassociated with corrosion rate is an intersection point atwhich the negative Tafel slope is extrapolated to corrosionpotential by the Tafel extrapolation method [34] This resultshowed that corrosion resistance of the Mg-35Zn-3Ca alloy

is much improved for the group that underwent solution heattreatment alone than in groups that underwent artificial agingheat treatment following solution heat treatment Whenimmersed in HBSS Mg undergoes anodic dissolution withthe release of H

2gas and generation of OHminus ions resulting

in an increase in pH of the medium [35] These reactionsequences can be represented as follows [36]

Anodic reaction Mg 997888rarr Mg2+ + 2e (6)

Cathodic reaction 2H2O + 2e 997888rarr H

2+ 2OHminus (7)

Formation of corrosion product

Mg2+ + 2OHminus 997888rarr Mg (OH)2

(8)

Thus the rate of corrosion of MgMg alloys could beestimated from the change in pH of the corrosive medium(HBSS in this study) as a function of time The change inpH of the HBSS measured as a function of time (Figure 6)showed that it is slowest for specimens in the T2 group whencompared to other groups This inference indicates that thecorrosion resistance is increased as the microstructure ofthe surface gets finer and denser The loss in weight of thespecimens measured after 5 days of immersion in HBSS is232mg(cm2 day) for the AT2 group which is significantlylower than that of the other groups (119875 lt 005) The lossin weight is 392mg(cm2 day) for the AT0 group whichis the highest among all the specimens tested Howeverthe difference between the specimens is insignificant whencomparedwith the specimens in other groups except with theAT2 group (119875 gt 005) Hence it is clear that the specimens ofthe AT2 group have offered an excellent corrosion resistancewhich is consistent with the results of change in pHHoweverthe results are inconsistent with those of the potentiodynamicpolarization test The fineness and homogeneity of the 120573phase largely determine the corrosion behavior which isreflected in the pH variation and weight loss These resultssupported that corrosion behavior of magnesium alloyswith multiphase structure is changed according to corro-sion potential difference distribution and volume fractionbetween micr-constituent phases [16 37 38] Since thesemeasurements are made for a long term the ability of the120573 phase to act as a physical barrier for corrosion becomeseffective [33 39] However during the electrochemical studysince the test is performed over a short duration the effect isnot reflected [29]

The hemolysis test which is conducted to assess thetoxicity to the body uses the principle that red blood cellsare divided or necrotized when the hemoglobin is destroyedThe concentration of free hemoglobin is proportional to thenumber of the injured RBC and the volume of the fluid [2440] The results of hemolysis test showed that the percentageof hemolysis (0147) in AT2 group is the lowest among allthe samples tested and when compared with other groups nostatistical significance difference could be observed (Figure 8Table 5) (119875 gt 005) In general if the hemolysis value is 5or less then it is considered as nonhemolytic according to

Advances in Materials Science and Engineering 9

ISO 10993-42002 [41] Accordingly the composition of Mg-35Zn-3Ca has low hemolysis and analogies good biocompat-ibility In other words homogenization and aging process ofthe Mg-35Zn-3Ca alloy can improve the physical propertiesand corrosion resistance of the material and it does not havea significant effect on the hemolytic toxicity

5 Conclusions

The preparation of Mg-35Zn-3Ca alloy containing zinc andcalcium rather than aluminum or RE elements as nontoxicand biocompatible alloying elements followed by heat treat-ment and artificial aging of the alloy to control its rate ofdegradation is reported The study leads to the followingconclusions

(1) DSC studies showed that the liquidus and solidustemperatures of the Mg-35Zn-3Ca alloy were36184∘C and 34011∘C respectively

(2) The microstructural features of the Mg-35Zn-3Caalloy indicate the presence of 120572-Mg matrix and 120573phase after heat treatment and artificial aging forvarious duration of time Among them the AT2group (heat treatment at 170∘C for 5 h followed byartificial aging at 310∘C for 48 h) exhibits the finest andmost homogenous distribution of 120572 and 120573 phases

(3) Potentiodynamic polarization studies of the Mg-35Zn-3Ca alloy specimens indicate that the 119894corr valuesof specimens that are heat-treated and artificiallyaged for different duration of time (AT1 to AT4) arerelatively higher than those subjected only to heattreatment (AT0) Among heat-treated and artificiallyaged samples (AT1 to AT4) specimens of the AT2group exhibit a lower 119894corr Based on the 119894corr valuesthe specimens can be ranked as follows AT0 gtAT2 gtAT3 gt AT4 gt AT1

(4) The change in pH of theHBSSmeasured for 72 h indi-cates that all the specimens exhibit a rapid increase inpH during the first 6 h during which the Mg-35Zn-3Ca alloy specimens subjected to heat treatment alone(AT0) showed a rapid increase in pH Beyond 48 hof immersion the pH of HBSS reached a stable valuefor all the specimens studied Among the AT1 toAT4 groups specimens of the AT2 group showed arelatively less increase in pH suggesting the lowerextent of dissolution of the Mg alloy

(5) Mg-35Zn-3Ca alloy specimens subjected to heattreatment alone (AT0) showed a corrosion rate of392mg(cm2 day) than those subjected to heat treat-ment followed by artificial aging for different dura-tions (AT1 to AT4) which ranges between 232 and373mg(cm2 day) Among the AT1 to AT4 groupsspecimens of theAT2 group showed a lower corrosionrate of 232mg(cm2 day) which is significantly lowerthan those of other groups (119875 lt 005)

(6) In vitro hemolysis test showed the lowest hemolysispercentage value of 0147 for the AT2 group but

the differences were statistically insignificant whencompared with that of other groups (119875 lt 005) Thehemolysis was 5 or less for all groups which indi-cates no significant hemoglobin destruction whichsuggests that Mg-35Zn-3Ca alloy has no cytotoxicity

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Authorsrsquo Contribution

Il-Song Park contributed to this work and is considered asjoint first author

Acknowledgments

This work was supported by the National Research Founda-tion of Korea (NRF) Grant funded by the Korea government(MSIP) (no 2011-0028709 and no 2014R1A4A1005309) andRegional Strategic Industry project (2013-R0002274)

References

[1] D A Puleo and W W Huh ldquoAcute toxicity of metal ions incultures of osteogenic cells derived from bone marrow stromalcellsrdquo Journal of Applied Biomaterials vol 6 no 2 pp 109ndash1161995

[2] J J Jacobs J L Gilbert and R M Urban ldquoCurrent conceptsreview Corrosion of metal orthopaedic implantsrdquo The Journalof Bone amp Joint Surgery vol 80 pp 268ndash282 1998

[3] C Lhotka T Szekeres I Steffan K Zhuber and K ZweymullerldquoFour-year study of cobalt and chromium blood levels inpatients managed with two different metal-on-metal total hipreplacementsrdquo Journal of Orthopaedic Research vol 21 no 2pp 189ndash195 2003

[4] J J Jacobs A K Skipor L M Patterson et al ldquoMetal releasein patients who have had a primary total hip arthroplasty Aprospective controlled longitudinal studyrdquoThe Journal of Boneand Joint SurgerymdashAmerican Volume vol 80 no 10 pp 1447ndash1458 1998

[5] J J Jacobs N J Hallab A K Skipor and R M UrbanldquoMetal degradation products a cause for concern in metal-metal bearingsrdquo Clinical Orthopaedics and Related Researchno 417 pp 139ndash147 2003

[6] J Nagels M Stokdijk and P M Rozing ldquoStress shielding andbone resorption in shoulder arthroplastyrdquo Journal of Shoulderand Elbow Surgery vol 12 no 1 pp 35ndash39 2003

[7] H G Seiler H Sigel and A Sigel Handbook on Toxicity ofInorganic Compounds 1988

[8] M P Staiger A M Pietak J Huadmai and G Dias ldquoMag-nesium and its alloys as orthopedic biomaterials a reviewrdquoBiomaterials vol 27 no 9 pp 1728ndash1734 2006

[9] E P DeGarmo J T Black and R A Kohser DeGarmorsquosMaterials and Processes in Manufacturing John Wiley amp Sons2011

[10] L J Gibson and M F Ashby Cellular Solids Structure andProperties Cambridge University Press 1999

10 Advances in Materials Science and Engineering

[11] J-W Choi Y-M Kong H-E Kim and I-S Lee ldquoReinforce-ment of hydroxyapatite bioceramic by addition of Ni

3

Al andAl2

O3

rdquo Journal of the American Ceramic Society vol 81 no 7pp 1743ndash1748 1998

[12] T Thamaraiselvi and S Rajeswari ldquoBiological evaluation ofbioceramic materialsmdasha reviewrdquo Trends in Biomaterials andArtificial Organs vol 18 no 1 pp 9ndash17 2004

[13] H Zreiqat C R Howlett A Zannettino et al ldquoMechanismsof magnesium-stimulated adhesion of osteoblastic cells tocommonly used orthopaedic implantsrdquo Journal of BiomedicalMaterials Research vol 62 no 2 pp 175ndash184 2002

[14] F Witte V Kaese H Haferkamp et al ldquoIn vivo corrosionof four magnesium alloys and the associated bone responserdquoBiomaterials vol 26 no 17 pp 3557ndash3563 2005

[15] C EWenMMabuchi Y Yamada K Shimojima Y Chino andT Asahina ldquoProcessing of biocompatible porous Ti and MgrdquoScripta Materialia vol 45 no 10 pp 1147ndash1153 2001

[16] G Song ldquoRecent progress in corrosion and protection ofmagnesium alloysrdquo Advanced Engineering Materials vol 7 no7 pp 563ndash586 2005

[17] S S A El-Rahman ldquoNeuropathology of aluminum toxicityin rats (glutamate and GABA impairment)rdquo PharmacologicalResearch vol 47 no 3 pp 189ndash194 2003

[18] Y Nakamura Y Tsumura Y Tonogai T Shibata and Y ItoldquoDifferences in behavior among the chlorides of seven rare earthelements administered intravenously to ratsrdquo Toxicological Sci-ences vol 37 no 2 pp 106ndash116 1997

[19] J Z Ilich and J E Kerstetter ldquoNutrition in bone health revisiteda story beyond calciumrdquo Journal of the American College ofNutrition vol 19 no 6 pp 715ndash737 2000

[20] J C Oh T Ohkubo T Mukai and K Hono ldquoTEM and 3DAPcharacterization of an age-hardened Mg-Ca-Zn alloyrdquo ScriptaMaterialia vol 53 no 6 pp 675ndash679 2005

[21] G Levi S Avraham A Zilberov and M Bamberger ldquoSolidifi-cation solution treatment and age hardening of a Mg-16 wtCa-32 wt Zn alloyrdquo Acta Materialia vol 54 no 2 pp 523ndash530 2006

[22] T Miyazaki J Kaneko and M Sugamata ldquoStructures andproperties of rapidly solidified Mg-Ca based alloysrdquo MaterialsScience and Engineering A vol 181-182 pp 1410ndash1414 1994

[23] C Liu Y Xin G Tang and P K Chu ldquoInfluence of heattreatment on degradation behavior of bio-degradable die-castAZ63 magnesium alloy in simulated body fluidrdquo MaterialsScience and Engineering A vol 456 no 1-2 pp 350ndash357 2007

[24] X Gu Y Zheng Y Cheng S Zhong and T Xi ldquoIn vitrocorrosion and biocompatibility of binary magnesium alloysrdquoBiomaterials vol 30 no 4 pp 484ndash498 2009

[25] B A Shaw Corrosion Resistance of Magnesium Alloys vol 13ASM handbook 2003

[26] V Kaesel P T Tai F Bach H Haferkamp F Witte and HWindhagen ldquoApproach to control the corrosion of magnesiumby alloyingrdquo inMagnesium Proceedings of the 6th InternationalConference Magnesium Alloys and Their Applications pp 534ndash539 Wiley Online Library 2004

[27] J E Gray and B Luan ldquoProtective coatings on magnesium andits alloysmdasha critical reviewrdquo Journal of Alloys and Compoundsvol 336 no 1-2 pp 88ndash113 2002

[28] M-C Zhao M Liu G Song and A Atrens ldquoInfluence of the120573-phase morphology on the corrosion of the Mg alloy AZ91rdquoCorrosion Science vol 50 no 7 pp 1939ndash1953 2008

[29] N N Aung andW Zhou ldquoEffect of heat treatment on corrosionand electrochemical behaviour of AZ91D magnesium alloyrdquoJournal of Applied Electrochemistry vol 32 no 12 pp 1397ndash14012002

[30] G Song A L Bowles and D H StJohn ldquoCorrosion resistanceof aged die cast magnesium alloy AZ91DrdquoMaterials Science andEngineering A vol 366 no 1 pp 74ndash86 2004

[31] M Jonsson D Persson and R Gubner ldquoThe initial steps ofatmospheric corrosion on magnesium alloy AZ91Drdquo Journal ofthe Electrochemical Society vol 154 no 11 pp C684ndashC691 2007

[32] T Beldjoudi C Fiaud and L Robbiola ldquoInfluence of homog-enization and artificial aging heat treatments on corrosionbehavior of Mg-Al alloysrdquo Corrosion vol 49 no 9 pp 738ndash7451993

[33] O Lunder J E Lein T K Aune and K Nisancioglu ldquoRole ofMg17Al12 phase in the corrosion of Mg alloy AZ91rdquo Corrosionvol 45 no 9 pp 741ndash748 1989

[34] D L Piron The Electrochemistry of Corrosion University ofHouston Houston Tex USA 1991

[35] G Song A Atrens D Stjohn J Nairn and Y Li ldquoThe electro-chemical corrosion of pure magnesium in 1 N NaClrdquo CorrosionScience vol 39 no 5 pp 855ndash875 1997

[36] Z Li X Gu S Lou and Y Zheng ldquoThe development of binaryMg-Ca alloys for use as biodegradable materials within bonerdquoBiomaterials vol 29 no 10 pp 1329ndash1344 2008

[37] A E Coy F Viejo P Skeldon and G E Thompson ldquoSus-ceptibility of rare-earth-magnesium alloys to micro-galvaniccorrosionrdquo Corrosion Science vol 52 no 12 pp 3896ndash39062010

[38] G Song and A Atrens ldquoUnderstanding magnesiumcorrosionmdasha framework for improved alloy performancerdquoAdvanced Engineering Materials vol 5 no 12 pp 837ndash8582003

[39] A F Crawley and K S Milliken ldquoPrecipitate morphology andorientation relationships in an agedMg-9Al-1 Zn-03Mnalloyrdquo Acta Metallurgica vol 22 no 5 pp 557ndash562 1974

[40] S O Sowemimo-Coker ldquoRed blood cell hemolysis duringprocessingrdquoTransfusionMedicine Reviews vol 16 no 1 pp 46ndash60 2002

[41] ISO ldquoBiological evaluation of medical devicesmdashPart 4 selec-tion of tests for interactions with bloodrdquo Tech Rep ISO 10993-4 2002

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CeramicsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CompositesJournal of

NanoparticlesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Biomaterials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MetallurgyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

MaterialsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nano

materials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofNanomaterials

Advances in Materials Science and Engineering 7

0 12 24 36 48 60 72

pH

Ageing time (hour)

7

8

9

10

11

AT0AT1AT2

AT3AT4

Figure 6 pH value as a function of immersion time

AT0 AT1 AT2 AT3 AT40

1

2

3

4

232

308308

373

Sample code

392

Cor

rosio

n ra

te (m

g(c

m2

day)

)

Figure 7 Corrosion rates of different heat treated Mg-35Zn-3Caalloys after immersion in HBSS for 5 days

that specimens subjected to heat treatment alone (AT0) showa higher corrosion rate (392mg(cm2 day)) when comparedto those subjected to heat treatment followed by artificialaging for different durations (AT1 to AT4) (ranging from232 to 373mg(cm2 day)) Among the AT1 to AT4 groupspecimens of the AT2 group showed a lower corrosion rate of232mg(cm2 day) which is significantly lower than those ofother groups (119875 lt 005)

In vitro hemolysis test is a well-known method to assessthe biotoxicity in a short duration of time The hemolysisability of Mg-35Zn-3Ca alloy specimens subjected to onlyheat treatment (AT0) and heat treatment followed by arti-ficial aging for different duration of time (AT1 to AT4) ismeasured using the positive (10mL saline solution containing01 wt of Na

2CO3) and negative (10mL saline solution)

as controls The measured optical density values and the

Table 5 Absorbance value measured at 540 nm and percentage ofhemolysis of Mg-35Zn-3Ca alloy subjected to heat treatment andartificial aging for different duration of time

Sample code OD at 540 nm Hemolysis ()AT0 0051 plusmn 0002 0515 plusmn 0375AT1 0050 plusmn 0002 0371 plusmn 0204AT2 0049 plusmn 0001 0147 plusmn 0104AT3 0050 plusmn 0001 0299 plusmn 0275AT4 0051 plusmn 0002 0521 plusmn 0272Negative 0049 plusmn 0001 0Positive 0495 plusmn 0013 100

hemolysis are compiled in Table 5 The variation in the hemolysis of all the samples tested alongwith the negative andpositive controls is plotted in Figure 8 for a better comparisonand to understand the statistical difference among themIt is evident from Table 5 and Figure 8 that among all thespecimens tested those belonging to the AT2 group showedthe lowest value of hemolysis (0147) However whencompared to other groups the difference in hemolysis isstatistically insignificant (119875 gt 005)

4 Discussion

Mg undergoes rapid corrosion in electrolytes containingchlorides such as body fluid Hence it will be difficult touse Mg for implant applications When Mg is exposed to airthe oxide layer formed on its surface offers only a partialprotection In aqueous solution the formation of porousMg(OH)

2layer could not offer much protection (equation

(3)) In presence of chloride ions it gets dissolved as MgCl2

while the aggressive nature of the medium causes severecorrosion of theMg (equations (4) and (5)) [25]The reactionsequences ofMg in aqueousmedium in the absence (equation(3)) and presence (equations (4) and (5)) of chloride ions canbe represented as follows [8]

Mg (solid) + 2H2O 997888rarr Mg (OH)

2+H2(gas) (3)

Mg (solid) + 2Clminus (aqueous) 997888rarr MgCl2

(4)

Mg (OH)2(solid) + 2Clminus 997888rarr MgCl

2 (5)

The corrosion resistance of Mg could be improvedthrough alloying formation of composites surface treat-ment and heat treatment [25ndash31] However the alloyingelements the second phase materials used to prepare thecomposites and the surface treated layer should not beharmful to the body when used as a biomaterial Someof the commonly used Mg-based alloys contain aluminumthat is harmful to the nervous system and osteoblasts whilethe RE-based Mg alloys could cause blood toxicity [1718] In the present study Mg-35Zn-3Ca alloy is preparedby adding zinc and calcium as alloying elements both ofwhich are nontoxic Alloying magnesium with zinc enablesprecipitation hardening while alloying with calcium couldhelp in grain refinement The microstructure and corrosion

8 Advances in Materials Science and Engineering

AT0 AT1 AT2 AT3 AT4 Negative Positive

0

1

2

90

100

05150371

01470299

0521

100

Hem

olys

is (

)

Sample code

0

Figure 8 Hemolysis percentage of various heat treated Mg-35Zn-3Ca alloys

resistance of the Mg-35Zn-3Ca alloy are evaluated aftersubjecting them to only heat treatment (AT0) and heattreatment and artificial aging for different duration of time(AT1 to AT4)

The microstructural examination after solution heattreatment and artificial aging heat treatment performed overa specific period of time showed that the 120572 and 120573 phaseswere finest and most homogenous in the AT2 group whichunderwent an artificial aging heat treatment at 170∘C for5 h Moreover the grain boundary was broken and 120573 phasewas inhomogeneous in the AT3 group which underwentartificial aging heat treatment for 75 h Results also showedthat the size of crystal grain became larger and the continuityof the crystal margin has disappeared in the AT4 groupwhich underwent artificial aging heat treatment for 10 h(Figure 3) Solution heat treatment is a process to preparethe supersaturated solid solution of unstable state materialsare generally softened by solution heat treatment Previousstudies have reported that artificial aging heat treatmentfollowing solution heat treatment of Mg alloy improvedstrength by refinement of the precipitate [29] Meanwhile itwas reported that heat treatment changed the microstruc-ture of alloy thereby affecting the corrosion behavior[32 33]

In this study potentiodynamic polarization studieschange in pH of HBSS and loss in weight after immersionin HBSS were used to assess the corrosion resistance of theMg-35Zn-3Ca alloy both in as-prepared and heat-treatedconditions The results of the potentiodynamic polarizationtest conducted to assess electrochemical corrosion behaviorshowed the lowest corrosion current density of 1011120583Acm2for the AT0 group which underwent only the solutionheat treatment Among the groups that underwent artificialaging following solution heat treatment the lowest corro-sion current density of 3641 120583Acm2 is observed for theAT2 group The corrosion current density which is closelyassociated with corrosion rate is an intersection point atwhich the negative Tafel slope is extrapolated to corrosionpotential by the Tafel extrapolation method [34] This resultshowed that corrosion resistance of the Mg-35Zn-3Ca alloy

is much improved for the group that underwent solution heattreatment alone than in groups that underwent artificial agingheat treatment following solution heat treatment Whenimmersed in HBSS Mg undergoes anodic dissolution withthe release of H

2gas and generation of OHminus ions resulting

in an increase in pH of the medium [35] These reactionsequences can be represented as follows [36]

Anodic reaction Mg 997888rarr Mg2+ + 2e (6)

Cathodic reaction 2H2O + 2e 997888rarr H

2+ 2OHminus (7)

Formation of corrosion product

Mg2+ + 2OHminus 997888rarr Mg (OH)2

(8)

Thus the rate of corrosion of MgMg alloys could beestimated from the change in pH of the corrosive medium(HBSS in this study) as a function of time The change inpH of the HBSS measured as a function of time (Figure 6)showed that it is slowest for specimens in the T2 group whencompared to other groups This inference indicates that thecorrosion resistance is increased as the microstructure ofthe surface gets finer and denser The loss in weight of thespecimens measured after 5 days of immersion in HBSS is232mg(cm2 day) for the AT2 group which is significantlylower than that of the other groups (119875 lt 005) The lossin weight is 392mg(cm2 day) for the AT0 group whichis the highest among all the specimens tested Howeverthe difference between the specimens is insignificant whencomparedwith the specimens in other groups except with theAT2 group (119875 gt 005) Hence it is clear that the specimens ofthe AT2 group have offered an excellent corrosion resistancewhich is consistent with the results of change in pHHoweverthe results are inconsistent with those of the potentiodynamicpolarization test The fineness and homogeneity of the 120573phase largely determine the corrosion behavior which isreflected in the pH variation and weight loss These resultssupported that corrosion behavior of magnesium alloyswith multiphase structure is changed according to corro-sion potential difference distribution and volume fractionbetween micr-constituent phases [16 37 38] Since thesemeasurements are made for a long term the ability of the120573 phase to act as a physical barrier for corrosion becomeseffective [33 39] However during the electrochemical studysince the test is performed over a short duration the effect isnot reflected [29]

The hemolysis test which is conducted to assess thetoxicity to the body uses the principle that red blood cellsare divided or necrotized when the hemoglobin is destroyedThe concentration of free hemoglobin is proportional to thenumber of the injured RBC and the volume of the fluid [2440] The results of hemolysis test showed that the percentageof hemolysis (0147) in AT2 group is the lowest among allthe samples tested and when compared with other groups nostatistical significance difference could be observed (Figure 8Table 5) (119875 gt 005) In general if the hemolysis value is 5or less then it is considered as nonhemolytic according to

Advances in Materials Science and Engineering 9

ISO 10993-42002 [41] Accordingly the composition of Mg-35Zn-3Ca has low hemolysis and analogies good biocompat-ibility In other words homogenization and aging process ofthe Mg-35Zn-3Ca alloy can improve the physical propertiesand corrosion resistance of the material and it does not havea significant effect on the hemolytic toxicity

5 Conclusions

The preparation of Mg-35Zn-3Ca alloy containing zinc andcalcium rather than aluminum or RE elements as nontoxicand biocompatible alloying elements followed by heat treat-ment and artificial aging of the alloy to control its rate ofdegradation is reported The study leads to the followingconclusions

(1) DSC studies showed that the liquidus and solidustemperatures of the Mg-35Zn-3Ca alloy were36184∘C and 34011∘C respectively

(2) The microstructural features of the Mg-35Zn-3Caalloy indicate the presence of 120572-Mg matrix and 120573phase after heat treatment and artificial aging forvarious duration of time Among them the AT2group (heat treatment at 170∘C for 5 h followed byartificial aging at 310∘C for 48 h) exhibits the finest andmost homogenous distribution of 120572 and 120573 phases

(3) Potentiodynamic polarization studies of the Mg-35Zn-3Ca alloy specimens indicate that the 119894corr valuesof specimens that are heat-treated and artificiallyaged for different duration of time (AT1 to AT4) arerelatively higher than those subjected only to heattreatment (AT0) Among heat-treated and artificiallyaged samples (AT1 to AT4) specimens of the AT2group exhibit a lower 119894corr Based on the 119894corr valuesthe specimens can be ranked as follows AT0 gtAT2 gtAT3 gt AT4 gt AT1

(4) The change in pH of theHBSSmeasured for 72 h indi-cates that all the specimens exhibit a rapid increase inpH during the first 6 h during which the Mg-35Zn-3Ca alloy specimens subjected to heat treatment alone(AT0) showed a rapid increase in pH Beyond 48 hof immersion the pH of HBSS reached a stable valuefor all the specimens studied Among the AT1 toAT4 groups specimens of the AT2 group showed arelatively less increase in pH suggesting the lowerextent of dissolution of the Mg alloy

(5) Mg-35Zn-3Ca alloy specimens subjected to heattreatment alone (AT0) showed a corrosion rate of392mg(cm2 day) than those subjected to heat treat-ment followed by artificial aging for different dura-tions (AT1 to AT4) which ranges between 232 and373mg(cm2 day) Among the AT1 to AT4 groupsspecimens of theAT2 group showed a lower corrosionrate of 232mg(cm2 day) which is significantly lowerthan those of other groups (119875 lt 005)

(6) In vitro hemolysis test showed the lowest hemolysispercentage value of 0147 for the AT2 group but

the differences were statistically insignificant whencompared with that of other groups (119875 lt 005) Thehemolysis was 5 or less for all groups which indi-cates no significant hemoglobin destruction whichsuggests that Mg-35Zn-3Ca alloy has no cytotoxicity

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Authorsrsquo Contribution

Il-Song Park contributed to this work and is considered asjoint first author

Acknowledgments

This work was supported by the National Research Founda-tion of Korea (NRF) Grant funded by the Korea government(MSIP) (no 2011-0028709 and no 2014R1A4A1005309) andRegional Strategic Industry project (2013-R0002274)

References

[1] D A Puleo and W W Huh ldquoAcute toxicity of metal ions incultures of osteogenic cells derived from bone marrow stromalcellsrdquo Journal of Applied Biomaterials vol 6 no 2 pp 109ndash1161995

[2] J J Jacobs J L Gilbert and R M Urban ldquoCurrent conceptsreview Corrosion of metal orthopaedic implantsrdquo The Journalof Bone amp Joint Surgery vol 80 pp 268ndash282 1998

[3] C Lhotka T Szekeres I Steffan K Zhuber and K ZweymullerldquoFour-year study of cobalt and chromium blood levels inpatients managed with two different metal-on-metal total hipreplacementsrdquo Journal of Orthopaedic Research vol 21 no 2pp 189ndash195 2003

[4] J J Jacobs A K Skipor L M Patterson et al ldquoMetal releasein patients who have had a primary total hip arthroplasty Aprospective controlled longitudinal studyrdquoThe Journal of Boneand Joint SurgerymdashAmerican Volume vol 80 no 10 pp 1447ndash1458 1998

[5] J J Jacobs N J Hallab A K Skipor and R M UrbanldquoMetal degradation products a cause for concern in metal-metal bearingsrdquo Clinical Orthopaedics and Related Researchno 417 pp 139ndash147 2003

[6] J Nagels M Stokdijk and P M Rozing ldquoStress shielding andbone resorption in shoulder arthroplastyrdquo Journal of Shoulderand Elbow Surgery vol 12 no 1 pp 35ndash39 2003

[7] H G Seiler H Sigel and A Sigel Handbook on Toxicity ofInorganic Compounds 1988

[8] M P Staiger A M Pietak J Huadmai and G Dias ldquoMag-nesium and its alloys as orthopedic biomaterials a reviewrdquoBiomaterials vol 27 no 9 pp 1728ndash1734 2006

[9] E P DeGarmo J T Black and R A Kohser DeGarmorsquosMaterials and Processes in Manufacturing John Wiley amp Sons2011

[10] L J Gibson and M F Ashby Cellular Solids Structure andProperties Cambridge University Press 1999

10 Advances in Materials Science and Engineering

[11] J-W Choi Y-M Kong H-E Kim and I-S Lee ldquoReinforce-ment of hydroxyapatite bioceramic by addition of Ni

3

Al andAl2

O3

rdquo Journal of the American Ceramic Society vol 81 no 7pp 1743ndash1748 1998

[12] T Thamaraiselvi and S Rajeswari ldquoBiological evaluation ofbioceramic materialsmdasha reviewrdquo Trends in Biomaterials andArtificial Organs vol 18 no 1 pp 9ndash17 2004

[13] H Zreiqat C R Howlett A Zannettino et al ldquoMechanismsof magnesium-stimulated adhesion of osteoblastic cells tocommonly used orthopaedic implantsrdquo Journal of BiomedicalMaterials Research vol 62 no 2 pp 175ndash184 2002

[14] F Witte V Kaese H Haferkamp et al ldquoIn vivo corrosionof four magnesium alloys and the associated bone responserdquoBiomaterials vol 26 no 17 pp 3557ndash3563 2005

[15] C EWenMMabuchi Y Yamada K Shimojima Y Chino andT Asahina ldquoProcessing of biocompatible porous Ti and MgrdquoScripta Materialia vol 45 no 10 pp 1147ndash1153 2001

[16] G Song ldquoRecent progress in corrosion and protection ofmagnesium alloysrdquo Advanced Engineering Materials vol 7 no7 pp 563ndash586 2005

[17] S S A El-Rahman ldquoNeuropathology of aluminum toxicityin rats (glutamate and GABA impairment)rdquo PharmacologicalResearch vol 47 no 3 pp 189ndash194 2003

[18] Y Nakamura Y Tsumura Y Tonogai T Shibata and Y ItoldquoDifferences in behavior among the chlorides of seven rare earthelements administered intravenously to ratsrdquo Toxicological Sci-ences vol 37 no 2 pp 106ndash116 1997

[19] J Z Ilich and J E Kerstetter ldquoNutrition in bone health revisiteda story beyond calciumrdquo Journal of the American College ofNutrition vol 19 no 6 pp 715ndash737 2000

[20] J C Oh T Ohkubo T Mukai and K Hono ldquoTEM and 3DAPcharacterization of an age-hardened Mg-Ca-Zn alloyrdquo ScriptaMaterialia vol 53 no 6 pp 675ndash679 2005

[21] G Levi S Avraham A Zilberov and M Bamberger ldquoSolidifi-cation solution treatment and age hardening of a Mg-16 wtCa-32 wt Zn alloyrdquo Acta Materialia vol 54 no 2 pp 523ndash530 2006

[22] T Miyazaki J Kaneko and M Sugamata ldquoStructures andproperties of rapidly solidified Mg-Ca based alloysrdquo MaterialsScience and Engineering A vol 181-182 pp 1410ndash1414 1994

[23] C Liu Y Xin G Tang and P K Chu ldquoInfluence of heattreatment on degradation behavior of bio-degradable die-castAZ63 magnesium alloy in simulated body fluidrdquo MaterialsScience and Engineering A vol 456 no 1-2 pp 350ndash357 2007

[24] X Gu Y Zheng Y Cheng S Zhong and T Xi ldquoIn vitrocorrosion and biocompatibility of binary magnesium alloysrdquoBiomaterials vol 30 no 4 pp 484ndash498 2009

[25] B A Shaw Corrosion Resistance of Magnesium Alloys vol 13ASM handbook 2003

[26] V Kaesel P T Tai F Bach H Haferkamp F Witte and HWindhagen ldquoApproach to control the corrosion of magnesiumby alloyingrdquo inMagnesium Proceedings of the 6th InternationalConference Magnesium Alloys and Their Applications pp 534ndash539 Wiley Online Library 2004

[27] J E Gray and B Luan ldquoProtective coatings on magnesium andits alloysmdasha critical reviewrdquo Journal of Alloys and Compoundsvol 336 no 1-2 pp 88ndash113 2002

[28] M-C Zhao M Liu G Song and A Atrens ldquoInfluence of the120573-phase morphology on the corrosion of the Mg alloy AZ91rdquoCorrosion Science vol 50 no 7 pp 1939ndash1953 2008

[29] N N Aung andW Zhou ldquoEffect of heat treatment on corrosionand electrochemical behaviour of AZ91D magnesium alloyrdquoJournal of Applied Electrochemistry vol 32 no 12 pp 1397ndash14012002

[30] G Song A L Bowles and D H StJohn ldquoCorrosion resistanceof aged die cast magnesium alloy AZ91DrdquoMaterials Science andEngineering A vol 366 no 1 pp 74ndash86 2004

[31] M Jonsson D Persson and R Gubner ldquoThe initial steps ofatmospheric corrosion on magnesium alloy AZ91Drdquo Journal ofthe Electrochemical Society vol 154 no 11 pp C684ndashC691 2007

[32] T Beldjoudi C Fiaud and L Robbiola ldquoInfluence of homog-enization and artificial aging heat treatments on corrosionbehavior of Mg-Al alloysrdquo Corrosion vol 49 no 9 pp 738ndash7451993

[33] O Lunder J E Lein T K Aune and K Nisancioglu ldquoRole ofMg17Al12 phase in the corrosion of Mg alloy AZ91rdquo Corrosionvol 45 no 9 pp 741ndash748 1989

[34] D L Piron The Electrochemistry of Corrosion University ofHouston Houston Tex USA 1991

[35] G Song A Atrens D Stjohn J Nairn and Y Li ldquoThe electro-chemical corrosion of pure magnesium in 1 N NaClrdquo CorrosionScience vol 39 no 5 pp 855ndash875 1997

[36] Z Li X Gu S Lou and Y Zheng ldquoThe development of binaryMg-Ca alloys for use as biodegradable materials within bonerdquoBiomaterials vol 29 no 10 pp 1329ndash1344 2008

[37] A E Coy F Viejo P Skeldon and G E Thompson ldquoSus-ceptibility of rare-earth-magnesium alloys to micro-galvaniccorrosionrdquo Corrosion Science vol 52 no 12 pp 3896ndash39062010

[38] G Song and A Atrens ldquoUnderstanding magnesiumcorrosionmdasha framework for improved alloy performancerdquoAdvanced Engineering Materials vol 5 no 12 pp 837ndash8582003

[39] A F Crawley and K S Milliken ldquoPrecipitate morphology andorientation relationships in an agedMg-9Al-1 Zn-03Mnalloyrdquo Acta Metallurgica vol 22 no 5 pp 557ndash562 1974

[40] S O Sowemimo-Coker ldquoRed blood cell hemolysis duringprocessingrdquoTransfusionMedicine Reviews vol 16 no 1 pp 46ndash60 2002

[41] ISO ldquoBiological evaluation of medical devicesmdashPart 4 selec-tion of tests for interactions with bloodrdquo Tech Rep ISO 10993-4 2002

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CeramicsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CompositesJournal of

NanoparticlesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Biomaterials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MetallurgyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

MaterialsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nano

materials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofNanomaterials

8 Advances in Materials Science and Engineering

AT0 AT1 AT2 AT3 AT4 Negative Positive

0

1

2

90

100

05150371

01470299

0521

100

Hem

olys

is (

)

Sample code

0

Figure 8 Hemolysis percentage of various heat treated Mg-35Zn-3Ca alloys

resistance of the Mg-35Zn-3Ca alloy are evaluated aftersubjecting them to only heat treatment (AT0) and heattreatment and artificial aging for different duration of time(AT1 to AT4)

The microstructural examination after solution heattreatment and artificial aging heat treatment performed overa specific period of time showed that the 120572 and 120573 phaseswere finest and most homogenous in the AT2 group whichunderwent an artificial aging heat treatment at 170∘C for5 h Moreover the grain boundary was broken and 120573 phasewas inhomogeneous in the AT3 group which underwentartificial aging heat treatment for 75 h Results also showedthat the size of crystal grain became larger and the continuityof the crystal margin has disappeared in the AT4 groupwhich underwent artificial aging heat treatment for 10 h(Figure 3) Solution heat treatment is a process to preparethe supersaturated solid solution of unstable state materialsare generally softened by solution heat treatment Previousstudies have reported that artificial aging heat treatmentfollowing solution heat treatment of Mg alloy improvedstrength by refinement of the precipitate [29] Meanwhile itwas reported that heat treatment changed the microstruc-ture of alloy thereby affecting the corrosion behavior[32 33]

In this study potentiodynamic polarization studieschange in pH of HBSS and loss in weight after immersionin HBSS were used to assess the corrosion resistance of theMg-35Zn-3Ca alloy both in as-prepared and heat-treatedconditions The results of the potentiodynamic polarizationtest conducted to assess electrochemical corrosion behaviorshowed the lowest corrosion current density of 1011120583Acm2for the AT0 group which underwent only the solutionheat treatment Among the groups that underwent artificialaging following solution heat treatment the lowest corro-sion current density of 3641 120583Acm2 is observed for theAT2 group The corrosion current density which is closelyassociated with corrosion rate is an intersection point atwhich the negative Tafel slope is extrapolated to corrosionpotential by the Tafel extrapolation method [34] This resultshowed that corrosion resistance of the Mg-35Zn-3Ca alloy

is much improved for the group that underwent solution heattreatment alone than in groups that underwent artificial agingheat treatment following solution heat treatment Whenimmersed in HBSS Mg undergoes anodic dissolution withthe release of H

2gas and generation of OHminus ions resulting

in an increase in pH of the medium [35] These reactionsequences can be represented as follows [36]

Anodic reaction Mg 997888rarr Mg2+ + 2e (6)

Cathodic reaction 2H2O + 2e 997888rarr H

2+ 2OHminus (7)

Formation of corrosion product

Mg2+ + 2OHminus 997888rarr Mg (OH)2

(8)

Thus the rate of corrosion of MgMg alloys could beestimated from the change in pH of the corrosive medium(HBSS in this study) as a function of time The change inpH of the HBSS measured as a function of time (Figure 6)showed that it is slowest for specimens in the T2 group whencompared to other groups This inference indicates that thecorrosion resistance is increased as the microstructure ofthe surface gets finer and denser The loss in weight of thespecimens measured after 5 days of immersion in HBSS is232mg(cm2 day) for the AT2 group which is significantlylower than that of the other groups (119875 lt 005) The lossin weight is 392mg(cm2 day) for the AT0 group whichis the highest among all the specimens tested Howeverthe difference between the specimens is insignificant whencomparedwith the specimens in other groups except with theAT2 group (119875 gt 005) Hence it is clear that the specimens ofthe AT2 group have offered an excellent corrosion resistancewhich is consistent with the results of change in pHHoweverthe results are inconsistent with those of the potentiodynamicpolarization test The fineness and homogeneity of the 120573phase largely determine the corrosion behavior which isreflected in the pH variation and weight loss These resultssupported that corrosion behavior of magnesium alloyswith multiphase structure is changed according to corro-sion potential difference distribution and volume fractionbetween micr-constituent phases [16 37 38] Since thesemeasurements are made for a long term the ability of the120573 phase to act as a physical barrier for corrosion becomeseffective [33 39] However during the electrochemical studysince the test is performed over a short duration the effect isnot reflected [29]

The hemolysis test which is conducted to assess thetoxicity to the body uses the principle that red blood cellsare divided or necrotized when the hemoglobin is destroyedThe concentration of free hemoglobin is proportional to thenumber of the injured RBC and the volume of the fluid [2440] The results of hemolysis test showed that the percentageof hemolysis (0147) in AT2 group is the lowest among allthe samples tested and when compared with other groups nostatistical significance difference could be observed (Figure 8Table 5) (119875 gt 005) In general if the hemolysis value is 5or less then it is considered as nonhemolytic according to

Advances in Materials Science and Engineering 9

ISO 10993-42002 [41] Accordingly the composition of Mg-35Zn-3Ca has low hemolysis and analogies good biocompat-ibility In other words homogenization and aging process ofthe Mg-35Zn-3Ca alloy can improve the physical propertiesand corrosion resistance of the material and it does not havea significant effect on the hemolytic toxicity

5 Conclusions

The preparation of Mg-35Zn-3Ca alloy containing zinc andcalcium rather than aluminum or RE elements as nontoxicand biocompatible alloying elements followed by heat treat-ment and artificial aging of the alloy to control its rate ofdegradation is reported The study leads to the followingconclusions

(1) DSC studies showed that the liquidus and solidustemperatures of the Mg-35Zn-3Ca alloy were36184∘C and 34011∘C respectively

(2) The microstructural features of the Mg-35Zn-3Caalloy indicate the presence of 120572-Mg matrix and 120573phase after heat treatment and artificial aging forvarious duration of time Among them the AT2group (heat treatment at 170∘C for 5 h followed byartificial aging at 310∘C for 48 h) exhibits the finest andmost homogenous distribution of 120572 and 120573 phases

(3) Potentiodynamic polarization studies of the Mg-35Zn-3Ca alloy specimens indicate that the 119894corr valuesof specimens that are heat-treated and artificiallyaged for different duration of time (AT1 to AT4) arerelatively higher than those subjected only to heattreatment (AT0) Among heat-treated and artificiallyaged samples (AT1 to AT4) specimens of the AT2group exhibit a lower 119894corr Based on the 119894corr valuesthe specimens can be ranked as follows AT0 gtAT2 gtAT3 gt AT4 gt AT1

(4) The change in pH of theHBSSmeasured for 72 h indi-cates that all the specimens exhibit a rapid increase inpH during the first 6 h during which the Mg-35Zn-3Ca alloy specimens subjected to heat treatment alone(AT0) showed a rapid increase in pH Beyond 48 hof immersion the pH of HBSS reached a stable valuefor all the specimens studied Among the AT1 toAT4 groups specimens of the AT2 group showed arelatively less increase in pH suggesting the lowerextent of dissolution of the Mg alloy

(5) Mg-35Zn-3Ca alloy specimens subjected to heattreatment alone (AT0) showed a corrosion rate of392mg(cm2 day) than those subjected to heat treat-ment followed by artificial aging for different dura-tions (AT1 to AT4) which ranges between 232 and373mg(cm2 day) Among the AT1 to AT4 groupsspecimens of theAT2 group showed a lower corrosionrate of 232mg(cm2 day) which is significantly lowerthan those of other groups (119875 lt 005)

(6) In vitro hemolysis test showed the lowest hemolysispercentage value of 0147 for the AT2 group but

the differences were statistically insignificant whencompared with that of other groups (119875 lt 005) Thehemolysis was 5 or less for all groups which indi-cates no significant hemoglobin destruction whichsuggests that Mg-35Zn-3Ca alloy has no cytotoxicity

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Authorsrsquo Contribution

Il-Song Park contributed to this work and is considered asjoint first author

Acknowledgments

This work was supported by the National Research Founda-tion of Korea (NRF) Grant funded by the Korea government(MSIP) (no 2011-0028709 and no 2014R1A4A1005309) andRegional Strategic Industry project (2013-R0002274)

References

[1] D A Puleo and W W Huh ldquoAcute toxicity of metal ions incultures of osteogenic cells derived from bone marrow stromalcellsrdquo Journal of Applied Biomaterials vol 6 no 2 pp 109ndash1161995

[2] J J Jacobs J L Gilbert and R M Urban ldquoCurrent conceptsreview Corrosion of metal orthopaedic implantsrdquo The Journalof Bone amp Joint Surgery vol 80 pp 268ndash282 1998

[3] C Lhotka T Szekeres I Steffan K Zhuber and K ZweymullerldquoFour-year study of cobalt and chromium blood levels inpatients managed with two different metal-on-metal total hipreplacementsrdquo Journal of Orthopaedic Research vol 21 no 2pp 189ndash195 2003

[4] J J Jacobs A K Skipor L M Patterson et al ldquoMetal releasein patients who have had a primary total hip arthroplasty Aprospective controlled longitudinal studyrdquoThe Journal of Boneand Joint SurgerymdashAmerican Volume vol 80 no 10 pp 1447ndash1458 1998

[5] J J Jacobs N J Hallab A K Skipor and R M UrbanldquoMetal degradation products a cause for concern in metal-metal bearingsrdquo Clinical Orthopaedics and Related Researchno 417 pp 139ndash147 2003

[6] J Nagels M Stokdijk and P M Rozing ldquoStress shielding andbone resorption in shoulder arthroplastyrdquo Journal of Shoulderand Elbow Surgery vol 12 no 1 pp 35ndash39 2003

[7] H G Seiler H Sigel and A Sigel Handbook on Toxicity ofInorganic Compounds 1988

[8] M P Staiger A M Pietak J Huadmai and G Dias ldquoMag-nesium and its alloys as orthopedic biomaterials a reviewrdquoBiomaterials vol 27 no 9 pp 1728ndash1734 2006

[9] E P DeGarmo J T Black and R A Kohser DeGarmorsquosMaterials and Processes in Manufacturing John Wiley amp Sons2011

[10] L J Gibson and M F Ashby Cellular Solids Structure andProperties Cambridge University Press 1999

10 Advances in Materials Science and Engineering

[11] J-W Choi Y-M Kong H-E Kim and I-S Lee ldquoReinforce-ment of hydroxyapatite bioceramic by addition of Ni

3

Al andAl2

O3

rdquo Journal of the American Ceramic Society vol 81 no 7pp 1743ndash1748 1998

[12] T Thamaraiselvi and S Rajeswari ldquoBiological evaluation ofbioceramic materialsmdasha reviewrdquo Trends in Biomaterials andArtificial Organs vol 18 no 1 pp 9ndash17 2004

[13] H Zreiqat C R Howlett A Zannettino et al ldquoMechanismsof magnesium-stimulated adhesion of osteoblastic cells tocommonly used orthopaedic implantsrdquo Journal of BiomedicalMaterials Research vol 62 no 2 pp 175ndash184 2002

[14] F Witte V Kaese H Haferkamp et al ldquoIn vivo corrosionof four magnesium alloys and the associated bone responserdquoBiomaterials vol 26 no 17 pp 3557ndash3563 2005

[15] C EWenMMabuchi Y Yamada K Shimojima Y Chino andT Asahina ldquoProcessing of biocompatible porous Ti and MgrdquoScripta Materialia vol 45 no 10 pp 1147ndash1153 2001

[16] G Song ldquoRecent progress in corrosion and protection ofmagnesium alloysrdquo Advanced Engineering Materials vol 7 no7 pp 563ndash586 2005

[17] S S A El-Rahman ldquoNeuropathology of aluminum toxicityin rats (glutamate and GABA impairment)rdquo PharmacologicalResearch vol 47 no 3 pp 189ndash194 2003

[18] Y Nakamura Y Tsumura Y Tonogai T Shibata and Y ItoldquoDifferences in behavior among the chlorides of seven rare earthelements administered intravenously to ratsrdquo Toxicological Sci-ences vol 37 no 2 pp 106ndash116 1997

[19] J Z Ilich and J E Kerstetter ldquoNutrition in bone health revisiteda story beyond calciumrdquo Journal of the American College ofNutrition vol 19 no 6 pp 715ndash737 2000

[20] J C Oh T Ohkubo T Mukai and K Hono ldquoTEM and 3DAPcharacterization of an age-hardened Mg-Ca-Zn alloyrdquo ScriptaMaterialia vol 53 no 6 pp 675ndash679 2005

[21] G Levi S Avraham A Zilberov and M Bamberger ldquoSolidifi-cation solution treatment and age hardening of a Mg-16 wtCa-32 wt Zn alloyrdquo Acta Materialia vol 54 no 2 pp 523ndash530 2006

[22] T Miyazaki J Kaneko and M Sugamata ldquoStructures andproperties of rapidly solidified Mg-Ca based alloysrdquo MaterialsScience and Engineering A vol 181-182 pp 1410ndash1414 1994

[23] C Liu Y Xin G Tang and P K Chu ldquoInfluence of heattreatment on degradation behavior of bio-degradable die-castAZ63 magnesium alloy in simulated body fluidrdquo MaterialsScience and Engineering A vol 456 no 1-2 pp 350ndash357 2007

[24] X Gu Y Zheng Y Cheng S Zhong and T Xi ldquoIn vitrocorrosion and biocompatibility of binary magnesium alloysrdquoBiomaterials vol 30 no 4 pp 484ndash498 2009

[25] B A Shaw Corrosion Resistance of Magnesium Alloys vol 13ASM handbook 2003

[26] V Kaesel P T Tai F Bach H Haferkamp F Witte and HWindhagen ldquoApproach to control the corrosion of magnesiumby alloyingrdquo inMagnesium Proceedings of the 6th InternationalConference Magnesium Alloys and Their Applications pp 534ndash539 Wiley Online Library 2004

[27] J E Gray and B Luan ldquoProtective coatings on magnesium andits alloysmdasha critical reviewrdquo Journal of Alloys and Compoundsvol 336 no 1-2 pp 88ndash113 2002

[28] M-C Zhao M Liu G Song and A Atrens ldquoInfluence of the120573-phase morphology on the corrosion of the Mg alloy AZ91rdquoCorrosion Science vol 50 no 7 pp 1939ndash1953 2008

[29] N N Aung andW Zhou ldquoEffect of heat treatment on corrosionand electrochemical behaviour of AZ91D magnesium alloyrdquoJournal of Applied Electrochemistry vol 32 no 12 pp 1397ndash14012002

[30] G Song A L Bowles and D H StJohn ldquoCorrosion resistanceof aged die cast magnesium alloy AZ91DrdquoMaterials Science andEngineering A vol 366 no 1 pp 74ndash86 2004

[31] M Jonsson D Persson and R Gubner ldquoThe initial steps ofatmospheric corrosion on magnesium alloy AZ91Drdquo Journal ofthe Electrochemical Society vol 154 no 11 pp C684ndashC691 2007

[32] T Beldjoudi C Fiaud and L Robbiola ldquoInfluence of homog-enization and artificial aging heat treatments on corrosionbehavior of Mg-Al alloysrdquo Corrosion vol 49 no 9 pp 738ndash7451993

[33] O Lunder J E Lein T K Aune and K Nisancioglu ldquoRole ofMg17Al12 phase in the corrosion of Mg alloy AZ91rdquo Corrosionvol 45 no 9 pp 741ndash748 1989

[34] D L Piron The Electrochemistry of Corrosion University ofHouston Houston Tex USA 1991

[35] G Song A Atrens D Stjohn J Nairn and Y Li ldquoThe electro-chemical corrosion of pure magnesium in 1 N NaClrdquo CorrosionScience vol 39 no 5 pp 855ndash875 1997

[36] Z Li X Gu S Lou and Y Zheng ldquoThe development of binaryMg-Ca alloys for use as biodegradable materials within bonerdquoBiomaterials vol 29 no 10 pp 1329ndash1344 2008

[37] A E Coy F Viejo P Skeldon and G E Thompson ldquoSus-ceptibility of rare-earth-magnesium alloys to micro-galvaniccorrosionrdquo Corrosion Science vol 52 no 12 pp 3896ndash39062010

[38] G Song and A Atrens ldquoUnderstanding magnesiumcorrosionmdasha framework for improved alloy performancerdquoAdvanced Engineering Materials vol 5 no 12 pp 837ndash8582003

[39] A F Crawley and K S Milliken ldquoPrecipitate morphology andorientation relationships in an agedMg-9Al-1 Zn-03Mnalloyrdquo Acta Metallurgica vol 22 no 5 pp 557ndash562 1974

[40] S O Sowemimo-Coker ldquoRed blood cell hemolysis duringprocessingrdquoTransfusionMedicine Reviews vol 16 no 1 pp 46ndash60 2002

[41] ISO ldquoBiological evaluation of medical devicesmdashPart 4 selec-tion of tests for interactions with bloodrdquo Tech Rep ISO 10993-4 2002

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CeramicsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CompositesJournal of

NanoparticlesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Biomaterials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MetallurgyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

MaterialsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nano

materials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofNanomaterials

Advances in Materials Science and Engineering 9

ISO 10993-42002 [41] Accordingly the composition of Mg-35Zn-3Ca has low hemolysis and analogies good biocompat-ibility In other words homogenization and aging process ofthe Mg-35Zn-3Ca alloy can improve the physical propertiesand corrosion resistance of the material and it does not havea significant effect on the hemolytic toxicity

5 Conclusions

The preparation of Mg-35Zn-3Ca alloy containing zinc andcalcium rather than aluminum or RE elements as nontoxicand biocompatible alloying elements followed by heat treat-ment and artificial aging of the alloy to control its rate ofdegradation is reported The study leads to the followingconclusions

(1) DSC studies showed that the liquidus and solidustemperatures of the Mg-35Zn-3Ca alloy were36184∘C and 34011∘C respectively

(2) The microstructural features of the Mg-35Zn-3Caalloy indicate the presence of 120572-Mg matrix and 120573phase after heat treatment and artificial aging forvarious duration of time Among them the AT2group (heat treatment at 170∘C for 5 h followed byartificial aging at 310∘C for 48 h) exhibits the finest andmost homogenous distribution of 120572 and 120573 phases

(3) Potentiodynamic polarization studies of the Mg-35Zn-3Ca alloy specimens indicate that the 119894corr valuesof specimens that are heat-treated and artificiallyaged for different duration of time (AT1 to AT4) arerelatively higher than those subjected only to heattreatment (AT0) Among heat-treated and artificiallyaged samples (AT1 to AT4) specimens of the AT2group exhibit a lower 119894corr Based on the 119894corr valuesthe specimens can be ranked as follows AT0 gtAT2 gtAT3 gt AT4 gt AT1

(4) The change in pH of theHBSSmeasured for 72 h indi-cates that all the specimens exhibit a rapid increase inpH during the first 6 h during which the Mg-35Zn-3Ca alloy specimens subjected to heat treatment alone(AT0) showed a rapid increase in pH Beyond 48 hof immersion the pH of HBSS reached a stable valuefor all the specimens studied Among the AT1 toAT4 groups specimens of the AT2 group showed arelatively less increase in pH suggesting the lowerextent of dissolution of the Mg alloy

(5) Mg-35Zn-3Ca alloy specimens subjected to heattreatment alone (AT0) showed a corrosion rate of392mg(cm2 day) than those subjected to heat treat-ment followed by artificial aging for different dura-tions (AT1 to AT4) which ranges between 232 and373mg(cm2 day) Among the AT1 to AT4 groupsspecimens of theAT2 group showed a lower corrosionrate of 232mg(cm2 day) which is significantly lowerthan those of other groups (119875 lt 005)

(6) In vitro hemolysis test showed the lowest hemolysispercentage value of 0147 for the AT2 group but

the differences were statistically insignificant whencompared with that of other groups (119875 lt 005) Thehemolysis was 5 or less for all groups which indi-cates no significant hemoglobin destruction whichsuggests that Mg-35Zn-3Ca alloy has no cytotoxicity

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Authorsrsquo Contribution

Il-Song Park contributed to this work and is considered asjoint first author

Acknowledgments

This work was supported by the National Research Founda-tion of Korea (NRF) Grant funded by the Korea government(MSIP) (no 2011-0028709 and no 2014R1A4A1005309) andRegional Strategic Industry project (2013-R0002274)

References

[1] D A Puleo and W W Huh ldquoAcute toxicity of metal ions incultures of osteogenic cells derived from bone marrow stromalcellsrdquo Journal of Applied Biomaterials vol 6 no 2 pp 109ndash1161995

[2] J J Jacobs J L Gilbert and R M Urban ldquoCurrent conceptsreview Corrosion of metal orthopaedic implantsrdquo The Journalof Bone amp Joint Surgery vol 80 pp 268ndash282 1998

[3] C Lhotka T Szekeres I Steffan K Zhuber and K ZweymullerldquoFour-year study of cobalt and chromium blood levels inpatients managed with two different metal-on-metal total hipreplacementsrdquo Journal of Orthopaedic Research vol 21 no 2pp 189ndash195 2003

[4] J J Jacobs A K Skipor L M Patterson et al ldquoMetal releasein patients who have had a primary total hip arthroplasty Aprospective controlled longitudinal studyrdquoThe Journal of Boneand Joint SurgerymdashAmerican Volume vol 80 no 10 pp 1447ndash1458 1998

[5] J J Jacobs N J Hallab A K Skipor and R M UrbanldquoMetal degradation products a cause for concern in metal-metal bearingsrdquo Clinical Orthopaedics and Related Researchno 417 pp 139ndash147 2003

[6] J Nagels M Stokdijk and P M Rozing ldquoStress shielding andbone resorption in shoulder arthroplastyrdquo Journal of Shoulderand Elbow Surgery vol 12 no 1 pp 35ndash39 2003

[7] H G Seiler H Sigel and A Sigel Handbook on Toxicity ofInorganic Compounds 1988

[8] M P Staiger A M Pietak J Huadmai and G Dias ldquoMag-nesium and its alloys as orthopedic biomaterials a reviewrdquoBiomaterials vol 27 no 9 pp 1728ndash1734 2006

[9] E P DeGarmo J T Black and R A Kohser DeGarmorsquosMaterials and Processes in Manufacturing John Wiley amp Sons2011

[10] L J Gibson and M F Ashby Cellular Solids Structure andProperties Cambridge University Press 1999

10 Advances in Materials Science and Engineering

[11] J-W Choi Y-M Kong H-E Kim and I-S Lee ldquoReinforce-ment of hydroxyapatite bioceramic by addition of Ni

3

Al andAl2

O3

rdquo Journal of the American Ceramic Society vol 81 no 7pp 1743ndash1748 1998

[12] T Thamaraiselvi and S Rajeswari ldquoBiological evaluation ofbioceramic materialsmdasha reviewrdquo Trends in Biomaterials andArtificial Organs vol 18 no 1 pp 9ndash17 2004

[13] H Zreiqat C R Howlett A Zannettino et al ldquoMechanismsof magnesium-stimulated adhesion of osteoblastic cells tocommonly used orthopaedic implantsrdquo Journal of BiomedicalMaterials Research vol 62 no 2 pp 175ndash184 2002

[14] F Witte V Kaese H Haferkamp et al ldquoIn vivo corrosionof four magnesium alloys and the associated bone responserdquoBiomaterials vol 26 no 17 pp 3557ndash3563 2005

[15] C EWenMMabuchi Y Yamada K Shimojima Y Chino andT Asahina ldquoProcessing of biocompatible porous Ti and MgrdquoScripta Materialia vol 45 no 10 pp 1147ndash1153 2001

[16] G Song ldquoRecent progress in corrosion and protection ofmagnesium alloysrdquo Advanced Engineering Materials vol 7 no7 pp 563ndash586 2005

[17] S S A El-Rahman ldquoNeuropathology of aluminum toxicityin rats (glutamate and GABA impairment)rdquo PharmacologicalResearch vol 47 no 3 pp 189ndash194 2003

[18] Y Nakamura Y Tsumura Y Tonogai T Shibata and Y ItoldquoDifferences in behavior among the chlorides of seven rare earthelements administered intravenously to ratsrdquo Toxicological Sci-ences vol 37 no 2 pp 106ndash116 1997

[19] J Z Ilich and J E Kerstetter ldquoNutrition in bone health revisiteda story beyond calciumrdquo Journal of the American College ofNutrition vol 19 no 6 pp 715ndash737 2000

[20] J C Oh T Ohkubo T Mukai and K Hono ldquoTEM and 3DAPcharacterization of an age-hardened Mg-Ca-Zn alloyrdquo ScriptaMaterialia vol 53 no 6 pp 675ndash679 2005

[21] G Levi S Avraham A Zilberov and M Bamberger ldquoSolidifi-cation solution treatment and age hardening of a Mg-16 wtCa-32 wt Zn alloyrdquo Acta Materialia vol 54 no 2 pp 523ndash530 2006

[22] T Miyazaki J Kaneko and M Sugamata ldquoStructures andproperties of rapidly solidified Mg-Ca based alloysrdquo MaterialsScience and Engineering A vol 181-182 pp 1410ndash1414 1994

[23] C Liu Y Xin G Tang and P K Chu ldquoInfluence of heattreatment on degradation behavior of bio-degradable die-castAZ63 magnesium alloy in simulated body fluidrdquo MaterialsScience and Engineering A vol 456 no 1-2 pp 350ndash357 2007

[24] X Gu Y Zheng Y Cheng S Zhong and T Xi ldquoIn vitrocorrosion and biocompatibility of binary magnesium alloysrdquoBiomaterials vol 30 no 4 pp 484ndash498 2009

[25] B A Shaw Corrosion Resistance of Magnesium Alloys vol 13ASM handbook 2003

[26] V Kaesel P T Tai F Bach H Haferkamp F Witte and HWindhagen ldquoApproach to control the corrosion of magnesiumby alloyingrdquo inMagnesium Proceedings of the 6th InternationalConference Magnesium Alloys and Their Applications pp 534ndash539 Wiley Online Library 2004

[27] J E Gray and B Luan ldquoProtective coatings on magnesium andits alloysmdasha critical reviewrdquo Journal of Alloys and Compoundsvol 336 no 1-2 pp 88ndash113 2002

[28] M-C Zhao M Liu G Song and A Atrens ldquoInfluence of the120573-phase morphology on the corrosion of the Mg alloy AZ91rdquoCorrosion Science vol 50 no 7 pp 1939ndash1953 2008

[29] N N Aung andW Zhou ldquoEffect of heat treatment on corrosionand electrochemical behaviour of AZ91D magnesium alloyrdquoJournal of Applied Electrochemistry vol 32 no 12 pp 1397ndash14012002

[30] G Song A L Bowles and D H StJohn ldquoCorrosion resistanceof aged die cast magnesium alloy AZ91DrdquoMaterials Science andEngineering A vol 366 no 1 pp 74ndash86 2004

[31] M Jonsson D Persson and R Gubner ldquoThe initial steps ofatmospheric corrosion on magnesium alloy AZ91Drdquo Journal ofthe Electrochemical Society vol 154 no 11 pp C684ndashC691 2007

[32] T Beldjoudi C Fiaud and L Robbiola ldquoInfluence of homog-enization and artificial aging heat treatments on corrosionbehavior of Mg-Al alloysrdquo Corrosion vol 49 no 9 pp 738ndash7451993

[33] O Lunder J E Lein T K Aune and K Nisancioglu ldquoRole ofMg17Al12 phase in the corrosion of Mg alloy AZ91rdquo Corrosionvol 45 no 9 pp 741ndash748 1989

[34] D L Piron The Electrochemistry of Corrosion University ofHouston Houston Tex USA 1991

[35] G Song A Atrens D Stjohn J Nairn and Y Li ldquoThe electro-chemical corrosion of pure magnesium in 1 N NaClrdquo CorrosionScience vol 39 no 5 pp 855ndash875 1997

[36] Z Li X Gu S Lou and Y Zheng ldquoThe development of binaryMg-Ca alloys for use as biodegradable materials within bonerdquoBiomaterials vol 29 no 10 pp 1329ndash1344 2008

[37] A E Coy F Viejo P Skeldon and G E Thompson ldquoSus-ceptibility of rare-earth-magnesium alloys to micro-galvaniccorrosionrdquo Corrosion Science vol 52 no 12 pp 3896ndash39062010

[38] G Song and A Atrens ldquoUnderstanding magnesiumcorrosionmdasha framework for improved alloy performancerdquoAdvanced Engineering Materials vol 5 no 12 pp 837ndash8582003

[39] A F Crawley and K S Milliken ldquoPrecipitate morphology andorientation relationships in an agedMg-9Al-1 Zn-03Mnalloyrdquo Acta Metallurgica vol 22 no 5 pp 557ndash562 1974

[40] S O Sowemimo-Coker ldquoRed blood cell hemolysis duringprocessingrdquoTransfusionMedicine Reviews vol 16 no 1 pp 46ndash60 2002

[41] ISO ldquoBiological evaluation of medical devicesmdashPart 4 selec-tion of tests for interactions with bloodrdquo Tech Rep ISO 10993-4 2002

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CeramicsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CompositesJournal of

NanoparticlesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Biomaterials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MetallurgyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

MaterialsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nano

materials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofNanomaterials

10 Advances in Materials Science and Engineering

[11] J-W Choi Y-M Kong H-E Kim and I-S Lee ldquoReinforce-ment of hydroxyapatite bioceramic by addition of Ni

3

Al andAl2

O3

rdquo Journal of the American Ceramic Society vol 81 no 7pp 1743ndash1748 1998

[12] T Thamaraiselvi and S Rajeswari ldquoBiological evaluation ofbioceramic materialsmdasha reviewrdquo Trends in Biomaterials andArtificial Organs vol 18 no 1 pp 9ndash17 2004

[13] H Zreiqat C R Howlett A Zannettino et al ldquoMechanismsof magnesium-stimulated adhesion of osteoblastic cells tocommonly used orthopaedic implantsrdquo Journal of BiomedicalMaterials Research vol 62 no 2 pp 175ndash184 2002

[14] F Witte V Kaese H Haferkamp et al ldquoIn vivo corrosionof four magnesium alloys and the associated bone responserdquoBiomaterials vol 26 no 17 pp 3557ndash3563 2005

[15] C EWenMMabuchi Y Yamada K Shimojima Y Chino andT Asahina ldquoProcessing of biocompatible porous Ti and MgrdquoScripta Materialia vol 45 no 10 pp 1147ndash1153 2001

[16] G Song ldquoRecent progress in corrosion and protection ofmagnesium alloysrdquo Advanced Engineering Materials vol 7 no7 pp 563ndash586 2005

[17] S S A El-Rahman ldquoNeuropathology of aluminum toxicityin rats (glutamate and GABA impairment)rdquo PharmacologicalResearch vol 47 no 3 pp 189ndash194 2003

[18] Y Nakamura Y Tsumura Y Tonogai T Shibata and Y ItoldquoDifferences in behavior among the chlorides of seven rare earthelements administered intravenously to ratsrdquo Toxicological Sci-ences vol 37 no 2 pp 106ndash116 1997

[19] J Z Ilich and J E Kerstetter ldquoNutrition in bone health revisiteda story beyond calciumrdquo Journal of the American College ofNutrition vol 19 no 6 pp 715ndash737 2000

[20] J C Oh T Ohkubo T Mukai and K Hono ldquoTEM and 3DAPcharacterization of an age-hardened Mg-Ca-Zn alloyrdquo ScriptaMaterialia vol 53 no 6 pp 675ndash679 2005

[21] G Levi S Avraham A Zilberov and M Bamberger ldquoSolidifi-cation solution treatment and age hardening of a Mg-16 wtCa-32 wt Zn alloyrdquo Acta Materialia vol 54 no 2 pp 523ndash530 2006

[22] T Miyazaki J Kaneko and M Sugamata ldquoStructures andproperties of rapidly solidified Mg-Ca based alloysrdquo MaterialsScience and Engineering A vol 181-182 pp 1410ndash1414 1994

[23] C Liu Y Xin G Tang and P K Chu ldquoInfluence of heattreatment on degradation behavior of bio-degradable die-castAZ63 magnesium alloy in simulated body fluidrdquo MaterialsScience and Engineering A vol 456 no 1-2 pp 350ndash357 2007

[24] X Gu Y Zheng Y Cheng S Zhong and T Xi ldquoIn vitrocorrosion and biocompatibility of binary magnesium alloysrdquoBiomaterials vol 30 no 4 pp 484ndash498 2009

[25] B A Shaw Corrosion Resistance of Magnesium Alloys vol 13ASM handbook 2003

[26] V Kaesel P T Tai F Bach H Haferkamp F Witte and HWindhagen ldquoApproach to control the corrosion of magnesiumby alloyingrdquo inMagnesium Proceedings of the 6th InternationalConference Magnesium Alloys and Their Applications pp 534ndash539 Wiley Online Library 2004

[27] J E Gray and B Luan ldquoProtective coatings on magnesium andits alloysmdasha critical reviewrdquo Journal of Alloys and Compoundsvol 336 no 1-2 pp 88ndash113 2002

[28] M-C Zhao M Liu G Song and A Atrens ldquoInfluence of the120573-phase morphology on the corrosion of the Mg alloy AZ91rdquoCorrosion Science vol 50 no 7 pp 1939ndash1953 2008

[29] N N Aung andW Zhou ldquoEffect of heat treatment on corrosionand electrochemical behaviour of AZ91D magnesium alloyrdquoJournal of Applied Electrochemistry vol 32 no 12 pp 1397ndash14012002

[30] G Song A L Bowles and D H StJohn ldquoCorrosion resistanceof aged die cast magnesium alloy AZ91DrdquoMaterials Science andEngineering A vol 366 no 1 pp 74ndash86 2004

[31] M Jonsson D Persson and R Gubner ldquoThe initial steps ofatmospheric corrosion on magnesium alloy AZ91Drdquo Journal ofthe Electrochemical Society vol 154 no 11 pp C684ndashC691 2007

[32] T Beldjoudi C Fiaud and L Robbiola ldquoInfluence of homog-enization and artificial aging heat treatments on corrosionbehavior of Mg-Al alloysrdquo Corrosion vol 49 no 9 pp 738ndash7451993

[33] O Lunder J E Lein T K Aune and K Nisancioglu ldquoRole ofMg17Al12 phase in the corrosion of Mg alloy AZ91rdquo Corrosionvol 45 no 9 pp 741ndash748 1989

[34] D L Piron The Electrochemistry of Corrosion University ofHouston Houston Tex USA 1991

[35] G Song A Atrens D Stjohn J Nairn and Y Li ldquoThe electro-chemical corrosion of pure magnesium in 1 N NaClrdquo CorrosionScience vol 39 no 5 pp 855ndash875 1997

[36] Z Li X Gu S Lou and Y Zheng ldquoThe development of binaryMg-Ca alloys for use as biodegradable materials within bonerdquoBiomaterials vol 29 no 10 pp 1329ndash1344 2008

[37] A E Coy F Viejo P Skeldon and G E Thompson ldquoSus-ceptibility of rare-earth-magnesium alloys to micro-galvaniccorrosionrdquo Corrosion Science vol 52 no 12 pp 3896ndash39062010

[38] G Song and A Atrens ldquoUnderstanding magnesiumcorrosionmdasha framework for improved alloy performancerdquoAdvanced Engineering Materials vol 5 no 12 pp 837ndash8582003

[39] A F Crawley and K S Milliken ldquoPrecipitate morphology andorientation relationships in an agedMg-9Al-1 Zn-03Mnalloyrdquo Acta Metallurgica vol 22 no 5 pp 557ndash562 1974

[40] S O Sowemimo-Coker ldquoRed blood cell hemolysis duringprocessingrdquoTransfusionMedicine Reviews vol 16 no 1 pp 46ndash60 2002

[41] ISO ldquoBiological evaluation of medical devicesmdashPart 4 selec-tion of tests for interactions with bloodrdquo Tech Rep ISO 10993-4 2002

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CeramicsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CompositesJournal of

NanoparticlesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Biomaterials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MetallurgyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

MaterialsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nano

materials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofNanomaterials

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CeramicsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CompositesJournal of

NanoparticlesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Biomaterials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MetallurgyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

MaterialsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nano

materials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofNanomaterials