ceramicsasbiomaterials

11

Ceramics as Ceramics as BiomaterialsBiomaterials

Guna SelvadurayGuna Selvaduray

MatE 175 MatE 175 –– Summer 2005Summer 2005

22G. G. Selvaduray Selvaduray –– SJSU SJSU –– MatE 175 MatE 175 –– Summer 2005Summer 2005

Examples of Ceramics in MedicineExamples of Ceramics in Medicine

Carriers for enzymes, antibodies, radiation sources

Insoluble glasses

Heart valvesCarbonsDental restorationsPorcelainBone replacementBioactive glasses

Bone repair and augmentation; surface coatings on metals

Calcium phosphateJoint replacementZirconia

Joint replacement, dental implants

AluminaApplication(s)Ceramic(s)

Source: J. R. Davis, p 3

In general, ceramics are used to repairor replace hard connective tissues


Source: Hench, p 2


Clinical success requires:

Achievement of a stable interface withconnective tissue

Functional match of the mechanical behaviorof the implant with the tissue to be replaced

Critical Issues:

Integrity of bioceramic

Interaction with the tissue


What are What are ““CeramicsCeramics””??MetalMetal--nonmetal compoundnonmetal compoundCrystalline and amorphous compoundsCrystalline and amorphous compoundsStoichiometricStoichiometric and and nonstoichiometricnonstoichiometric compoundscompoundsThermodynamic stabilityThermodynamic stabilityInertnessInertnessRelative lack of toxicityRelative lack of toxicityVery low leach ratesVery low leach ratesMechanical characteristicsMechanical characteristics

StrongStrongHardHardBrittleBrittle

PorosityPorosity


Ceramics Basics Ceramics Basics -- CrystallographyCrystallographyRock Salt Structure Fluorite Structure Corundum Structure

Source: Chiang, Bernie & Kingery


Features of Compound Crystal Features of Compound Crystal StructuresStructures

Anions and Anions and cationscations at fixed locationsat fixed locationsCharge neutrality requirementCharge neutrality requirement

Determines sites that are filledDetermines sites that are filledNot all sites are always filledNot all sites are always filledAbility to add solutesAbility to add solutesSites occupied by solutesSites occupied by solutes


Amorphous ceramicsAmorphous ceramicsAkaAka glassesglassesLacks long range Lacks long range orderorder

Typically silicatesTypically silicatesTTgg

Softening pointSoftening point

Source: Callister p 57

Network former

Bridging oxygen bond

Nonbridging oxygenbond

Network modifier


StoichiometricStoichiometric & & NonstoichiometricNonstoichiometric CompoundsCompounds

Determined by number of valence Determined by number of valence states of states of cationcation

Stoichiometric Compounds

Al2O3ZrO2TiO2Y2O3

Nonstoichiometric Compounds

FeOCuO


Thermodynamic StabilityThermodynamic Stability

Criterion: Criterion: ∆∆GGoof,298f,298

AlAl22OO33::--378 kcal/mole 378 kcal/mole →→ 126 kcal/g atom O126 kcal/g atom OZrOZrO22: : --248 kcal/mole 248 kcal/mole →→ 124 kcal/g atom O124 kcal/g atom OSiOSiO22: : --196 kcal/mole 196 kcal/mole →→ 98 kcal/g atom O98 kcal/g atom ORelationship between thermodynamic stability Relationship between thermodynamic stability and inertness, leach rateand inertness, leach rate

Source: BOM Bulletin 605


Mechanical CharacteristicsMechanical Characteristics

Lack of ability to deform plastically due to Lack of ability to deform plastically due to dislocation pinningdislocation pinningGriffithGriffith’’s Flawss FlawsBrittle behaviorBrittle behaviorTest methods: Flexure strengthTest methods: Flexure strength33--point and 4point and 4--point bend testspoint bend testsWeibullWeibull Modulus for characterizing Modulus for characterizing mechanical behavior/reliability of ceramicsmechanical behavior/reliability of ceramics


FabricationFabrication

Starting point: powdersStarting point: powdersFormation of Formation of ““green productgreen product””SinteringSinteringPore formation and porosityPore formation and porosityPore size controlPore size control““Porosity is a way of lifePorosity is a way of life””


Factors affecting ImplantFactors affecting Implant--Tissue Tissue Interfacial ResponseInterfacial Response

Mechanical LoadMechanical Load

Closeness of FitCloseness of Fit

Chemical ReactionsMotion at Interface

Surface PorosityBlood Circulation at Interface

Surface MorphologyBlood Circulation in Tissue

Phase BoundariesAge of Tissue

Phases in ImplantHealth of Tissue

Composition of ImplantType of Tissue

Implant SideTissue Side

Source: Hench, p 4


ImplantImplant--Tissue InteractionsTissue Interactions

Tissue replaces implantDissolution of implant

Tissue forms an interfacial bond with the implantBioactive

Tissue forms a non-adherent fibrous capsule around the implant

Biologically (nearly) inert

Tissue diesToxic

ConsequenceImplant-Tissue Reaction

Source: Hench p 4


ImplantImplant--Tissue ResponseTissue ResponseToxic:Toxic: surrounding tissue dies; implant material must avoid toxic surrounding tissue dies; implant material must avoid toxic response that kills cells in the surrounding tissues or releasesresponse that kills cells in the surrounding tissues or releaseschemicals that can migrate within fluidschemicals that can migrate within fluids

Biologically inactiveBiologically inactive (and non(and non--toxic): formation of a nontoxic): formation of a non--adherent fibrous capsule to adherent fibrous capsule to ““wallwall--offoff”” or isolate implant from or isolate implant from hosthost

Biologically active Biologically active (bioactive): bond forms across interface (bioactive): bond forms across interface between implant and tissue; prevents relative motion between between implant and tissue; prevents relative motion between the two; bioactive interfaces can change with timethe two; bioactive interfaces can change with time

DissolutionDissolution: Implant dissolves or : Implant dissolves or resorbsresorbs and is replaced by the and is replaced by the surrounding tissue; surrounding tissue; resorbableresorbable material must be of a composition material must be of a composition that can be degraded chemically by bodily fluids; degradation that can be degraded chemically by bodily fluids; degradation products must be nontoxic chemically and be easily disposed of products must be nontoxic chemically and be easily disposed of without damage to cellswithout damage to cells


BioceramicBioceramic--Tissue AttachmentTissue Attachment

Morphological fixationMorphological fixationBiological fixationBiological fixationBioactive fixationBioactive fixationDissolution/ReplacementDissolution/Replacement


Morphological FixationMorphological Fixation

Implant is inert or nearly inertImplant is inert or nearly inertDevice cemented into tissue, or pressDevice cemented into tissue, or press--fitfitDevice: dense, nonporous, nearly inertDevice: dense, nonporous, nearly inertAttachment: bone growth into surface irregularitiesAttachment: bone growth into surface irregularitiesMechanism: mechanical interlockingMechanism: mechanical interlockingDoes not form bond with tissue (bone)Does not form bond with tissue (bone)Tissue response is dependent on fit rather than Tissue response is dependent on fit rather than chemistrychemistryIf interfacial movement occurs, fibrous capsule If interfacial movement occurs, fibrous capsule becomes several 100 becomes several 100 µµm thick, implant loosensm thick, implant loosensExample: single crystal and polycrystalline AlExample: single crystal and polycrystalline Al22OO33

http://www.materials.qmul.ac.uk/casestud/implants/index.php


It is possible to combine the best mechanical properties of all the materials described and good engineering design in order to produce an implant with the optimum chance of long term clinical survival. Here is an example of such a 'hybrid' implant. It is a cobalt chromium Freeman, with a ceramic femoral head, hydroxyapatite coating and a nitrided surface finish, which hardens the surface of the stem and helps prevent scratching and the release of metal wear debris. However, there is one more parameter, which plays an important role in implant design, that is cost. Material scientists are constantly faced with the challenge of producing optimum material properties at minimum cost.

http://www.materials.qmul.ac.uk/casestud/implants/index.php


Biological FixationBiological Fixation

Forms mechanical attachment via bone Forms mechanical attachment via bone ““ingrowthingrowth”” into into poresporesPores must be > 100 Pores must be > 100 µµm diameter so that capillaries m diameter so that capillaries can provide blood supply to ingrown connective tissuecan provide blood supply to ingrown connective tissuePorous inert implantsPorous inert implantsTissue response is complex, with several factors Tissue response is complex, with several factors affecting itaffecting itHydroxyapatiteHydroxyapatite coated porous implantscoated porous implantsOptimization Issue: large volume fraction of pores Optimization Issue: large volume fraction of pores desirable for stable interfacial bone growth, but desirable for stable interfacial bone growth, but pores also degrade strengthpores also degrade strength


Bioactive FixationBioactive FixationSurfaceSurface--reactive materials; elicits a specific biological response reactive materials; elicits a specific biological response at the surfaceat the surfaceDirect attachment by chemical bonding with boneDirect attachment by chemical bonding with boneImplant reacts chemically, at the surfaceImplant reacts chemically, at the surfaceDense, nonporousDense, nonporousCapsule formation is minimal because of the removal of the Capsule formation is minimal because of the removal of the influence of interfacial movement by the bonding mechanisminfluence of interfacial movement by the bonding mechanismFactors: time dependence of bonding, strength of bond, Factors: time dependence of bonding, strength of bond, mechanism of bonding, thickness of bonding zonemechanism of bonding, thickness of bonding zoneBioactive glasses, bioactive glassBioactive glasses, bioactive glass--ceramics (ceramics (CeravitalCeravital), ), hydroxyapatitehydroxyapatite ((DuraptiteDuraptite. . CalcitekCalcitek); bioactive composites ); bioactive composites ((PalavitalPalavital) ) Formation of a Formation of a hydroxyhydroxy--carbonate apatite (HCA) on surface, carbonate apatite (HCA) on surface, when implantedwhen implanted


Dissolution/ReplacementDissolution/ReplacementResorbableResorbable ceramics slowly replaced by boneceramics slowly replaced by boneDesigned to degrade with time, and replaced with natural Designed to degrade with time, and replaced with natural tissuestissuesResorptionResorption rates must match rates must match ““repairrepair”” rates of body tissuerates of body tissueConstituents of Constituents of resorbableresorbable implant must be metabolically implant must be metabolically acceptableacceptableReactions will persist until components have been removedReactions will persist until components have been removedDense, porous/nonporousDense, porous/nonporousExamples: Calcium sulfate, Examples: Calcium sulfate, tricalciumtricalcium phosphate (TCP), phosphate (TCP), calcium phosphate saltscalcium phosphate saltsChallenge: Meeting strength requirements and shortChallenge: Meeting strength requirements and short--term term mechanical performance while regeneration of tissues is mechanical performance while regeneration of tissues is occuringoccuring


Specific Specific BioceramicsBioceramics

Alumina Alumina –– AlAl22OO33

ZirconiaZirconia –– ZrOZrO22

Bioactive glassesBioactive glasses


Alumina Alumina -- 11

Applications Applications –– loadload--bearingbearingHip prostheses, approximately 300,000 in 1997Hip prostheses, approximately 300,000 in 1997Knee prosthesesKnee prosthesesAnkle, elbows, shoulders, wrists, finger jointsAnkle, elbows, shoulders, wrists, finger jointsBone screws, etc.Bone screws, etc.

High density, high purity (<0.5% impurities)High density, high purity (<0.5% impurities)AlAl22OO33 is inert because of its thermodynamic stability; is inert because of its thermodynamic stability; not not ““attackedattacked”” by longby long--term exposure to physiological term exposure to physiological environmentenvironmentCorrosion resistant, wear resistant, high strengthCorrosion resistant, wear resistant, high strength100% testing100% testing


http://www.prozyr.com/PAGES_UK/Biomedical/outline.htm

http://adam.about.com/encyclopedia/9494.htm?terms=knee+prostheses

http://adam.about.com/surgery/100088.htm

http://www.handuniversity.com/topics.asp?Topic_ID=22


Alumina Alumina -- 22

Production: Pressed & sintered at ~ 1600Production: Pressed & sintered at ~ 1600ooCCPurity and grain size are important Purity and grain size are important –– affects affects strength, fatigue resistance, fracture strength, fatigue resistance, fracture toughnesstoughness<0.5% <0.5% MgOMgO added as sintering aid and to limit added as sintering aid and to limit grain growth during sinteringgrain growth during sinteringSiO2 + alkali oxides: < 0.1 %SiO2 + alkali oxides: < 0.1 %

They promote grain growthThey promote grain growthStrength, fatigue resistance, fracture Strength, fatigue resistance, fracture toughness = toughness = f(purityf(purity, grain size, density), grain size, density)


8Weibull Modulus

5 ~ 6 (4.5 ~ 5.5)Fracture toughness (KIC, Mpa√m, ksi√in)

380 (55)380 (55.2)Young’s Modulus (GPa, psi x 106)

400 (58)400 (58)550 (80)Bending strength (MPA, ksi)

4 (580)4.5 (653)Compressive strength (GPa, ksi)

18 GPa> 2,0002,300Vickers hardness

0.02Surface roughness (Ra, μm)

≤ 4.5< 73 ~ 6Average grain size (μm)3.94≥ 3.90> 3.93Density (g/cm3)

≥ 99.5≥ 99.5< 99.8Alumina content (%)

ASTM F 603ISO 6474High-alumina ceramics

Property

Source: J.R. Davis, p 140-141


TribologyTribology (friction and wear)(friction and wear)

Excellent Excellent tribologicaltribological propertiespropertiesSmall grain size required (< 4Small grain size required (< 4µµm) with narrow m) with narrow distributiondistributionLow surface roughness (RLow surface roughness (Raa ≤≤ 0.02 0.02 µµm)m)

Lower is betterLower is betterHigh surface energy of Al2O3 results in fast and High surface energy of Al2O3 results in fast and strong adsorption of biological molecules strong adsorption of biological molecules –– limits limits direct contact of articulating surfacesdirect contact of articulating surfacesBallBall--socket combinations are polished together socket combinations are polished together and used as a pairand used as a pair


Source: Ratner, p 158


ZirconiaZirconia

Articulating ball in total hip prosthesesArticulating ball in total hip prosthesesInert due to thermodynamic stabilityInert due to thermodynamic stabilityPressed and sintered at ~ 1400Pressed and sintered at ~ 1400ooCCPhase transformation at ~ 1000Phase transformation at ~ 1000ooCCStabilizer added to partially suppress phase Stabilizer added to partially suppress phase transformationtransformation

YttriaYttria –– YY22OO33CalciaCalcia –– CaOCaO

Transformation toughening utilized to improve Transformation toughening utilized to improve fracture toughnessfracture toughnessLower elastic modulus (compared to Al2O3) leads to Lower elastic modulus (compared to Al2O3) leads to less stress shieldingless stress shielding


AlAl22OO33 & ZrO& ZrO22: Limitations: Limitations

Restricted to designs involving Restricted to designs involving compressive loading or limited tensile compressive loading or limited tensile loadsloads

Ceramics are generally weak in tensionCeramics are generally weak in tensionAvoid applications where impact loading Avoid applications where impact loading is a possibilityis a possibility

Low resilience, fracture toughnessLow resilience, fracture toughness


AlAl22OO33 & ZrO& ZrO22: Limitations: LimitationsHigh Elastic Modulus of AlHigh Elastic Modulus of Al22OO33 and ZrOand ZrO22 can can lead to Stress Shieldinglead to Stress Shielding

High Elastic Modulus limits their High Elastic Modulus limits their effectiveness as bone interface materialseffectiveness as bone interface materials

760 ~ 7600 for cancellous bone15 ~ 55 times for cortical boneModulus mismatch

150 ~ 208PSZ380 ~ 420Medical grade Al2O3

7 ~ 25Cortical bone0.05 ~ 0.5Cancellous bone

Elastic Modulus (GPa)Material


BioglassBioglass

BioglassesBioglasses develop a reactive layer with develop a reactive layer with a gela gel--like structure when in contact with like structure when in contact with body fluids and tissuesbody fluids and tissuesThis provides a compliant interface This provides a compliant interface between the bulk glass and tissuebetween the bulk glass and tissueThe surface forms a biologically active The surface forms a biologically active HA layer that provides the bonding HA layer that provides the bonding interface with tissuesinterface with tissues


BioglassBioglass UsesUses

Replacement for Replacement for ossiclesossicles in the middle earin the middle earFilling of defect created in the jaw when a tooth is Filling of defect created in the jaw when a tooth is removedremovedSoft tissue seal for implants which pass through the Soft tissue seal for implants which pass through the skin, e.g., electrodesskin, e.g., electrodesTreatment of periodontal diseasesTreatment of periodontal diseasesRapid rate of surface reaction leads to fast tissue Rapid rate of surface reaction leads to fast tissue bondingbondingMechanical weakness and low fracture toughness Mechanical weakness and low fracture toughness makes it unsuitable for load bearing applicationsmakes it unsuitable for load bearing applicationsSuitable as a coating for implants in lowSuitable as a coating for implants in low--loaded or loaded or compressively loaded devicescompressively loaded devices


BioglassBioglass CompositionCompositionProduced by conventional glass Produced by conventional glass manufacturing methodsmanufacturing methodsCompositional limitations:Compositional limitations:

< 60 mol % SiO< 60 mol % SiO22High NaHigh Na22O and O and CaOCaOHigh CaO/PHigh CaO/P22OO55 ratioratio

Biological behavior dependent on Biological behavior dependent on composition, especially relative composition, especially relative proportion of bridging oxygen bonds proportion of bridging oxygen bonds to nonto non--bridging bondsbridging bonds


Composition dependence of Composition dependence of biological activitybiological activity

Region A: Bioactive Region A: Bioactive bone bonding regionbone bonding regionRegion B: Typical Region B: Typical silicate glasses; nearly silicate glasses; nearly inert; fibrous capsule inert; fibrous capsule formation at implantformation at implant--tissue interfacetissue interfaceRegion C: Region C: ResorbableResorbable; ; disappears in 10 ~ 30 disappears in 10 ~ 30 days after implantation days after implantation

Source: J.R. Davis, p 143

Entire composition contains 6 % P2O5


BioglassBioglass 45S545S5

45S: 45 wt% network former, i.e., SiO45S: 45 wt% network former, i.e., SiO22

5: 5 to 1 molar ratio of 5: 5 to 1 molar ratio of CaOCaO to Pto P22OO55SiOSiO22 45%45%NaNa22OO 24.5%24.5%CaOCaO 24.4%24.4%PP22OO55 6%6%


Reaction StagesReaction Stages

Stage 1Stage 1: Ion exchange between alkali : Ion exchange between alkali ions from the glass and hydrogen ions ions from the glass and hydrogen ions from the solutionfrom the solution

SiSi--OO--NaNa++ + H+ H++ + OH+ OH-- →→SiSi--OHOH++ + Na+ Na++ (solution) + OH(solution) + OH--

Reaction is diffusion controlled, rate of Reaction is diffusion controlled, rate of alkali extraction is parabolic alkali extraction is parabolic –– dependent on dependent on tt--½½


Stage 2Stage 2: Interfacial network : Interfacial network dissolution; dissolution; siloxanesiloxane ((SiSi--OO--SiSi) bonds are ) bonds are broken, forming large concentration of broken, forming large concentration of surface surface silanolsilanol ((SiSi--OH) groupsOH) groups

SiSi--OO--SiSi + H+ H22O O →→ SiSi--OH + OHOH + OH--SiSiKinetics: linearKinetics: linear

Stage 3Stage 3: Condensation of : Condensation of silanolssilanols to to form a hydrated silica gelform a hydrated silica gel

SiSi--OH + OhOH + Oh--SiSi →→ SiSi--OO--SiSi + H+ H22OOKinetics: Interface controlledKinetics: Interface controlled


Stage 4Stage 4: Formation of an amorphous : Formation of an amorphous calcium phosphate layercalcium phosphate layer

Migration of CaMigration of Ca2+2+ and POand PO4433-- groups to the groups to the

surface through the SiOsurface through the SiO22--rich layer rich layer forming a CaOforming a CaO--PP22OO55--rich film on top of the rich film on top of the SiOSiO22--rich layer, followed by growth of the rich layer, followed by growth of the amorphous CaOamorphous CaO--PP22OO55--rich film by rich film by incorporation of soluble calcium and incorporation of soluble calcium and phosphates from solutionphosphates from solution


Stage 5Stage 5: Crystallization of a : Crystallization of a hydroxycarbonatehydroxycarbonate apatiteapatite (HCA) layer(HCA) layer

Carbonate anions (COCarbonate anions (CO3322--)substitute for OH)substitute for OH-- in the in the

apatiteapatite crystal structure to form HCAcrystal structure to form HCACrystallization of HCA occurs around collagen Crystallization of HCA occurs around collagen fibrils present at the implant interface, leading to fibrils present at the implant interface, leading to interface bondinginterface bonding

For bonding with tissue, a layer of biologically For bonding with tissue, a layer of biologically active HCA must formactive HCA must formRate of tissue bonding depends on rate of Rate of tissue bonding depends on rate of HCA formationHCA formation


HydroxyapatitesHydroxyapatitesChemically similar to mineral component of bonesChemically similar to mineral component of bonesBioactive: will support bone Bioactive: will support bone ingrowthingrowth and and osseointegrationosseointegration when used in when used in orthopaedicorthopaedic, dental and , dental and maxillofacialmaxillofacial applicationsapplicationsChemical formulaChemical formula: : CaCa1010(PO(PO44))66(OH)(OH)22Hexagonal Hexagonal BravaisBravais lattice, space group P6lattice, space group P633/m/mThe chemical nature of The chemical nature of hydroxyapatitehydroxyapatite lends itself to lends itself to substitution; common substitutions involve carbonate, substitution; common substitutions involve carbonate, fluoride and chloride substitutions for hydroxyl fluoride and chloride substitutions for hydroxyl groupsgroupsDense Dense hydroxyapatitehydroxyapatite does not have the mechanical does not have the mechanical strength to enable it to succeed in long term load strength to enable it to succeed in long term load bearing applications. bearing applications.


Uses for HAUses for HAFacial augmentation with Facial augmentation with hydroxyapatitehydroxyapatite has been has been used for the following corrections: Cheek, Chin, Jaw, used for the following corrections: Cheek, Chin, Jaw, Nose, Nose, BrowboneBrowboneSkeletal repair Skeletal repair resorbableresorbablebiomaterialsbiomaterialsOcular prosthesis Ocular prosthesis

HydroxyapatiteHydroxyapatite from coralfrom coralThe eye muscles can beThe eye muscles can be

attached directly to thisattached directly to thisimplant, allowing it to moveimplant, allowing it to move

within the orbitwithin the orbit-- just likejust likethe natural eye. the natural eye.

http://www.ioi.com/


Calcium Phosphate Calcium Phosphate BioceramicsBioceramicsThere are several calcium phosphate ceramics that are consideredThere are several calcium phosphate ceramics that are consideredbiocompatible; most are biocompatible; most are resorbableresorbable and will dissolve when exposed to and will dissolve when exposed to physiological environments. physiological environments. Order of solubility: Order of solubility: TetracalciumTetracalcium Phosphate (Ca4P2O9) > Amorphous Phosphate (Ca4P2O9) > Amorphous calcium Phosphate > alphacalcium Phosphate > alpha--TricalciumTricalcium Phosphate (Ca3(PO4)2) > betaPhosphate (Ca3(PO4)2) > beta--TricalciumTricalcium Phosphate (Ca3(PO4) 2) >> Phosphate (Ca3(PO4) 2) >> HydroxyapatiteHydroxyapatite(Ca10(PO4)6(OH)2)(Ca10(PO4)6(OH)2)HydroxyapatiteHydroxyapatite is thermodynamically stable at physiological pH values; is thermodynamically stable at physiological pH values; actively takes part in bone bonding, forming strong chemical bonactively takes part in bone bonding, forming strong chemical bonds with ds with surrounding bonesurrounding boneMechanical properties unsuitable for loadMechanical properties unsuitable for load--bearing applications such as bearing applications such as orthopaedicsorthopaedicsUsed as a coating on materials such as titanium and titanium allUsed as a coating on materials such as titanium and titanium alloys, oys, where it can contribute its 'bioactive' properties, while the mewhere it can contribute its 'bioactive' properties, while the metallic tallic component bears the loadcomponent bears the loadCoatings applied by plasma spraying; careful control of processiCoatings applied by plasma spraying; careful control of processing ng parameters is necessary to prevent thermal decomposition of parameters is necessary to prevent thermal decomposition of hydroxyapatitehydroxyapatite into other soluble calcium phosphates due to the high into other soluble calcium phosphates due to the high processing temperatures.processing temperatures.

Source: http://Source: http://www.azom.com/details.asp?ArticleIDwww.azom.com/details.asp?ArticleID=1743=1743

4444G. G. Selvaduray Selvaduray –– SJSU SJSU –– MatE 175 MatE 175 –– Summer 2005Summer 2005Source: Hench, page 145


Biological Biological ApatitesApatites

Mineral phases of calcified tissue Mineral phases of calcified tissue ––enamel, dentin, boneenamel, dentin, boneReferred to as Referred to as hydroxyapatitehydroxyapatite –– HAHABiological Biological apatitesapatites differ from differ from synthesized synthesized apatitesapatitesEnamel, dentin and bone Enamel, dentin and bone HAsHAs differ in differ in crystallinitycrystallinity and concentration of COand concentration of CO33

22--

and Mgand Mg2+2+


Bone Dentin Enamel


Synthesis of Dense HASynthesis of Dense HA

Sequence:Sequence:PowderPowderGreen ProductGreen ProductSintered ProductSintered Product

Methods:Methods:PrecipitationPrecipitationSolid State ReactionSolid State Reaction


PrecipitationPrecipitation10Ca(OH)10Ca(OH)22 + 3H+ 3H33(PO(PO44))22 →→ CaCa1010(PO(PO44))66(OH)(OH)22

10Ca(NO10Ca(NO33))22 + 6(NH+ 6(NH44)2HPO)2HPO44 + 2NH+ 2NH44OH OH →→HAHA

Solid State ReactionsSolid State Reactions6CaHPO6CaHPO44 + 4Ca(OH)+ 4Ca(OH)22 →→ CaCa1010(PO(PO44))66(OH)(OH)22 + + 6H6H22OO3Ca3Ca33(PO(PO44))22 + Ca(OH)+ Ca(OH)22 →→ CaCa1010(PO(PO44))66(OH)(OH)22 + + HH22OO


Compaction and SinteringCompaction and SinteringDense HA:Dense HA:

< 5% porosity< 5% porositymax pore size: < 1 max pore size: < 1 µµmm

Compaction: 60 ~ 80 Compaction: 60 ~ 80 MPaMPaBindersBinders

1 % cornstarch + water1 % cornstarch + waterStearicStearic acid in alcoholacid in alcoholLow molecular weight hydrocarbonsLow molecular weight hydrocarbons

Sintering: 950 ~ 1300Sintering: 950 ~ 1300ooC, air, several hoursC, air, several hoursProducts prepared in net shape, or milled from Products prepared in net shape, or milled from sintered blockssintered blocksASTM F1185ASTM F1185--88: min 95% HA, < 5% 88: min 95% HA, < 5% ββ--TCPTCP

Impurities: As (3), Impurities: As (3), CdCd (5), (5), HfHf (5), (5), PbPb (30) (30) ppmppm


Porous HAPorous HA

Natural bone: ~ 70 wt% HA (~ 50 Natural bone: ~ 70 wt% HA (~ 50 volvol%)%)Bone regeneration takes place in the poresBone regeneration takes place in the poresMin pore size: 100 Min pore size: 100 µµmmInterconnected porous system necessaryInterconnected porous system necessaryProcessing: sintered HAProcessing: sintered HA

IsostaticIsostatic compaction and sintering of powders with compaction and sintering of powders with naphthalene particlesnaphthalene particlesNaphthalene volatilizes, leaving interconnected Naphthalene volatilizes, leaving interconnected porespores

ceramicsasbiomaterials

Documents

Transcript of ceramicsasbiomaterials