8/4/2019 Biotribological Behavior of Ultra High Molecular Weight
1/7
Received 07 April 2008; accepted 12 June 2008
Projects 50535050 supported by the National Natural Science Foundation of China and NCET-06-0479 by the New Century Excellent Talents in University
Corresponding author. Tel: +86-516-83591915; E-mail address: [email protected]
Biotribological behavior of ultra high molecular weight
polyethylene composites containing bovine bone hydroxyapatite
LIU Jin-long, ZHU Yuan-yuan, WANG Qing-liang, GE Shi-rong
School of Materials and Engineering, China University of Mining & Technology, Xuzhou, Jiangsu 221008, China
Abstract: Wear particles of ultrahigh molecular weight polyethylene (UHMWPE) are the main cause of long-term failure of totaljoint replacements. Therefore, increasing its wear resistance or bioactivity will be very useful in order to obtain high quality artifi-cial joints. In our study, UHMWPE composites filled with the bovine bone hydroxyapatite (BHA) were prepared by the method ofcompression moulding. A ball-on-disc wear test was carried out with a Universal Micro-Tribometer to investigate the friction and
wear behavior of a Si3N4 ceramic ball, cross-sliding against the UHMWPE/BHA composites with human plasma lubrication. At the
same time, the profiles of the worn grooves on the UHMWPE/BHA surface were scanned. The experimental results indicate thatthe addition of BHA to UHMWPE had a significant effect on the biotribological behavior of UHMWPE cross-sliding against theSi3N4 ceramic ball. The addition of BHA powder enhanced the hardness and modulus of elasticity of these composites and de-creased the friction coefficients and wear rates under conditions of human plasma lubrication. When the added amount of BHA
powders was up to 20%~30%, UHMWPE/BHA composites demonstrated the designed performance of the mechanical propertiesand biotribological behavior.Key words: UHMWPE; hydroxyapatite; biotribology; composite material
1 Introduction
Ultra high molecular weight polyethylene
(UHMWPE) is an organic polymer widely used as anacetabular component in hip and total knee joint re-
placements, because of its excellent mechanical prop-erties, biocompatibility and stability in the humanbody
[12]. However, in recent years it has been recog-
nized that the wear debris of UHMWPE may be alimiting factor for the long-term success of prostheses.
At Present, most clinical results have revealed thataseptic loosening is the primary cause of failure of
total hip replacements (THRs) and accounts for al-most three-quarters of all revision operations
[36].
Aseptic loosening has been strongly linked with
UHMWPE wear debris-induced osteolysis and sincethe occurrence and severity of osteolysis appears tobe related to the size and concentration of wear parti-
cles, it follows that reducing the amount and rate ofgeneration of wear particles should reduce the occur-
rence of long-term aseptic loosening[78]
. Therefore, it
is believed that two effective methods to reduce asep-tic loosening are the following:
1) improving the wear resistance to reduce the
concentration of wear debris.
2) increasing the biocompatibility and bioactivityto decrease adverse biological reactions.
Since the wear resistance of UHMWPE appears to
be related to its mechanical properties, especiallythose on the surface, it follows that an increased en-
hancement of its mechanical properties should im-
prove the wear resistance of UHMWPE. Many au-thors have reported that the mechanical properties of
UHMWPE composites can be improved by introduc-ing reinforced second phases of ceramics (A12O3,
TiO2, quartz, wollastonite, etc.), metals or polymers
(polyurethane, phenylp-hydroxyzoate, etc.)[915]
. The
results show that these reinforced second phases mayimprove not only the mechanical properties but also
the wear performance of UHMWPE-based compos-ites. But, most of these filling materials have no or at
best poor biocompatibility and bioactivity.Hydroxyapatite (HA) is currently used as a bioma-
terial for many applications in biomedicine, becauseit can form a real bond with the surrounding bonetissue when implanted
[16]. Several studies on
UHMWPE/HA composites have been reported. Reis
et al. investigated the impact behavior of aHA/UHMWPE composite
[17]. Cunha et al. studied the
effect of processing conditions on the mechanical
J China Univ Mining & Technol 18 (2008) 06060612
JOURNAL OF CHINA UNIVERSITY OF
MINING &
TECHNOLOGY
www.elsevier.com/locate/jcumt
8/4/2019 Biotribological Behavior of Ultra High Molecular Weight
2/7
LIU Jin-long et al Biotribological behavior of ultra high molecular weight polyethylene 607
behavior of the HA/UHMWPE composite using in-jection and compression molding
[18]. However, few of
these efforts are related to the natural bone hy-
droxyapatite, which has been used as bone implantmaterial due to its improved bioactivity, structure and
components, similar to that of human bones. Knets etal. produced an annealed compact bone tissue rein-
forced UHMWPE composite, but few processing de-
tails were given[19]
.In order to improve the wear resistance and bioac-
tivity of UHMWPE and reduce aseptic loosening,bovine bone hydroxyapatite (BHA) powders (
8/4/2019 Biotribological Behavior of Ultra High Molecular Weight
3/7
Journal of China University of Mining & Technology Vol.18 No.4608
2.2 Friction and wear test
A ball-on-disc wear test was run on a Universal
Micro-Tribometer (Center Inc. USA) to investigatethe friction and wear behavior of the Si3N4 ceramic
ball, cross-sliding against UHMWPE/BHA compos-ites with human plasma lubrication (see Fig. 3a). The
reciprocating velocity of the upper sample is 8 mm/s,
reciprocating distance 0.2 mm and sliding speed of
lower sample 0.21 m/s. In sliding bearing, sliding
wear in a rotational direction is normally noticed. But
the bending deflection in the axial direction willcause friction and wear. So, the friction and wear be-
havior of UNMWPE/BHA composites under cross-sliding direction conditions have been studied for the
movement of artificial knee joints and hip joints, in-
cluding tangential and radial loads.
(a) Schematic diagram (b) Wear track
Fig. 3 Schematic diagram of abrasion testing and wear track on UHMWPE/BHA composite disc
The Si3N4 ceramic ball was 4 mm in diameter and
fixed on the load arm. The UHMWPE/BHA compos-ite disc was rotated by an electrical motor controlled
by a frequency converter. Fig. 3b shows that, when
the disc is rotated along the circumference of a circle,the Si3N4 ceramic ball cross-slid ten times. The con-
tact load was 3.9 N and the sliding speed 0.21 m/s.The testing time was 120 min in each test. All ex-
periments were performed in human plasma lubrica-
tion at room temperature. The relative humidity was50%~60%. Each wear test was repeated at least three
times. Prior to the wear testing, each of the
UHMWPE composite discs was ground to obtain asmooth surface. Grinding was performed in steps
with abrasive papers of decreasing grit size. Theground surfaces were polished with a diamond paste
with particle sizes of 0.35 m on a nylon polishing
cloth. The average surface roughness, Ra of the pol-ished surfaces was less than 0.2 m, measured using
a conventional profilometer.In order to normalize the wear results in our study,
the commonly used wear rate k was calculated bydividing the reduced wear weight m (BP211D elec-tron analytical balance with 0.01 mg precision,
Sartorius AG, Germany) by the product of total
sliding distance S, the applied normal load Nandthe density of the material
[20]: k =m /NS.
Analysis of variance using regression analysis andStudents t-test was carried out to test for significant
differences between various sets of experimental data.A probability level ofp
8/4/2019 Biotribological Behavior of Ultra High Molecular Weight
4/7
LIU Jin-long et al Biotribological behavior of ultra high molecular weight polyethylene 609
Fig. 4 Effect of amount of BHA on hardness and modulusof elasticity of UHMWPE/BHA composites
3.2 Friction coefficients
The friction coefficients of UHMWPE/BHA com-
posites of Si3N4 with human plasma lubrication at
room temperature are shown in Fig. 5a. Each of theUHMWPE/BHA composites had the same change in
the friction coefficients over time. The friction coeffi-
cients decreased rapidly for a short time of slidingand then tended to reach a steady state at about 60
min. The variation of the friction coefficient for all
materials fluctuated little during the entire wearprocess. From the average friction coefficients in Fig.
5b, it is seen that the addition of BHA clearly de-creased the friction coefficients of the UHMWPE/
BHA composites against Si3N4. When the amount of
BHA was up to 20%~30%, the lowest friction coeffi-cient was obtained. For example, the friction coeffi-
cient of UHMWPE was approximately 0.064, butonly about 0.042 and 0.048 for UHMWPE/20% BHA
and UHMWPE/30% BHA composites respectively,
which is only about 60% of that of UHMWPE.However, when the increased amount of BHA ex-ceeded 30%, the friction coefficient values increased
with the increment in the amount of BHA.
(a) Friction coefficients (b) Steady friction coefficients
Fig. 5 Friction coefficients of UHMWPE/BHA cross-sliding against Si3N4 ceramic in human plasma lubrication and steady
friction coefficients acquired by calculating the average friction coefficients between 60 and 120 min of sliding time
3.3 Wear behavior
The bar charts in Fig. 6 present the wear rates ofUHMWPE/BHA composites with human plasma lu-
brication. It clearly shows that the addition of BHA to
UHMWPE can raise the wear rates of these compos-
ites. When the amount of BHA was less than 30%,the wear rate of the composite would reduce with anincrease in the amount of BHA. The sample of
UHMWPE/20% BHA material had a wear rate of7.6110
8mm
3/Nm, which was only about 60% of
the 12.38108
mm3/Nm of UHMWPE. It also shows
that the wear rate increases with an increase in the
amount of BHA when it exceeds 30%. But, these de-creases were clearly less than that of UHMWPE. In
addition, under the cross-sliding movement the wearrate of UHMWPE was higher than that in a single
bearing slide[21]
.
Worn grooves on UHMWPE/BHA composite sur-faces are presented in Fig. 7. Although it was difficult
to position the boundary of the worn groove exactly,
these worn-out areas still demonstrate that worn
grooves from UHMWPE were deeper or wider thanthose of UHMWPE/BHA composites. Composites
with lower wear rates show narrower and shallower
worn grooves, which agreed with the wear rates inour tests.
Fig. 6 Comparison on wear rate of UHMWPE/BHA
composites cross-sliding against Si3N4
8/4/2019 Biotribological Behavior of Ultra High Molecular Weight
5/7
Journal of China University of Mining & Technology Vol.18 No.4610
m
m
m
m
m
m
m
m
m
m
m
m
Fig. 7 Profiles of worn grooves on UHMWPE/BHA composite surfaces with human plasma lubrication
4 Discussion
The experimental results from our tests indicatethat the addition of BHA to UHMWPE had a signifi-
cant effect on the wear and friction behavior of
UHMWPE cross-sliding against the Si3N4 ceramicball. It clearly showed that the addition of BHA pow-
der enhances the hardness and modulus of elasticityof these composites and decreased both the friction
coefficients and wear rates with human plasma lubri-cation. When the amount of BHA reached 20%~30%,the UHMWPE/BHA composites demonstrated thedesigned performance of the mechanical propertiesand biotribological behavior.
It is well known that the friction force of
UHMWPE polymers against ceramic balls is com- posed of interfacial adhesion and ploughing forces.
The adhesion force is affected by the effective
modulus of elasticity, i.e., there is an inversely pro- portional relationship. The ploughing force depends
on the shear strength of UHMWPE surfaces. It is seenfrom Fig. 4 that the modulus of elastiocity of the sur-face of UHMWPE/BHA composites increases along
with enhanced surface hardness. The modulus ofelasticity of the surface increased from 720 to 1077
MPa, while the hardness increased from 117 to 133MPa. In some experiments
[22]it was reported that the
gamma irradiated UHMWPE has a modulus of sur-
face elasticity of approximately 1200 for untreatedspecimens, 1450 for specimens treated with 75 kGy
and 1530 MPa for a treatment of 150 kGy, corre-
sponding to a surface hardness of about 37, 46 and 54,respectively. (The variation in the data for UHMWPEmight be related to the different method of prepara-
tion). For this reason, the increment in the effectivemodulus of elasticity might reduce the adhesive force
of the Si3N4 ceramic ball on UHMWPE/BHA com-
posite surfaces. At the same time, the hardened sur-face can increase the ploughing force against the hard
asperity of the surface of the Si3N4 ball with the
hardness enhancement of the UHMWPE/BHA com- posite surface. Consequently, the summation of the
adhesion and ploughing forces resulted in the lowfriction coefficients for UHMWPE/BHA composites
in Fig. 5.
The pictures in Fig. 8 show the two worn surfaces
of UHMWPE and UHMWPE/20% BHA. It is seenfrom Fig. 8a that the worn surface of UHMWPE hasa rough worn appearance, including adhered debris,
serious grooves and fatigue fractures, almost all on
the worn surfaces. For UHMWPE/BHA composite,the worn scars have become less so, owing to its sur-face hardness enhancement. The smoother worn sur-
face appears by reason of the shallow grooves. Theadhered debris and fatigue fractures could be found
only in one small worn-out area in Fig. 8b. Theseresults are likely caused by the decrease in the wear
rate of this material. When the Si3N4 ball was rubbing
on the UHMWPE/BHA surface, the wear resistance
of polymer was inversely proportional to its hardness.With an increase in hardness and the modulus of elas-ticity shown in Fig. 4, the enhancement of ploughingand adhesive wear resistance could have resulted in
the lower wear rates of UHMWPE/BHA composites.Meanwhile, low wear rates of UHMWPE against
the ceramic ball were contributed by the deposition of
protein and other organic contents in plasma from the plasma lubrication. Some authors reported that the
serum protein concentration had a significant effecton the wear performance of CoCr alloys to PTFE
polymer and the film deposited by the serum protein
might affect the wear of UHMWPE[2325]. For theUHMWPE/BHA composites, the biocompatibility
and bioactivity of BHA resulted in a good bonding
ability to the mass of the proteins in human plasma,
8/4/2019 Biotribological Behavior of Ultra High Molecular Weight
6/7
LIU Jin-long et al Biotribological behavior of ultra high molecular weight polyethylene 611
which greatly increased the ability of these compos-ites to absorb the plasma protein. The concentration
of the protein deposition enhanced with an increase of
the amount of HA[23]
. The protein deposition in hu-man plasma lubrication made it possible to form a
thin protective film, reducing the abrasion of theSi3N4 ball on UHMWPE surface. Furthermore, lower
wear rates of UHMWPE/BHA composites were ob-
tained in human plasma lubrication and the greaterthe additive amount, the lower the wear rates. How-
ever, when the amount of BHA was greater than the
optimum amount, the wear resistance of UHMWPE/BHA composite decreased due to their lower hard-
ness and modulus of elasticity, as shown in Figs. 4and 6.
(a) UHMWPE (b) UHMWPE/BHA 20%
Fig. 8 SEM micrographs of worn surfaces of UHMWPE cross-sliding against Si3N4 ceramic
5 Conclusions
1) The addition of BHA powder to UHMWPE hasshown to be beneficial for increasing its mi-
cro-surface mechanical properties. When the amount
of BHA was less than 30%, the hardness and modulusof elasticity clearly improved. For the UHMWPE/
20%BHA composite, the micro-surface hardness and
modulus of elasticity were about 15% and 50%higher than that of pure UHMWPE.
2) With human plasma lubrication, the addition ofBHA to UHMWPE was effective in decreasing the
friction coefficients and wear rates of UHMWPE/
BHA composites cross-sliding against the Si3N4 ce-ramic ball. Reduction of 40% in the wear rate was
obtained for the UHMWPE/20% BHA composite.3) Ploughing and fatigue fracture were the main
wear mechanisms of the UHMWPE/BHA composites
cross-sliding against the Si3N4 ceramic with humanplasma lubrication.
Acknowledgements
The authors wish to thank for the support from Na-
tional Nature Science Foundation of China(50535050) and Program for New Century Excellent
Talents in University (NCET-06-0479).
References
[1] Cooper J R, Dowson D, Fisher J. Macroscopic and mi-
croscopic wear mechanisms in ultra-high molecularweight polyethylene. Wear, 1993, 162/164 (part 1): 378384.
[2] Krzypow D J, Timnacc M. Cyclic steady state stress-
strain behavior of UHMW polyethylene. Biomaterials,
2000, 21(20): 20812087.
[3] Sawae Y, Murakami T, Doi S. Worn surface characteris-tics of ultra-high molecular weight polyethylene lubri-
catedwith bovine serum. Tribology and Interface Engi-
neering Series, 2000(38): 347356.[4] McGee M A, Howie D W, Neade S D, et al. The role of
polyethylene wear in joint failure. Proc Instn MechEngrs, 1997, 211(1): 6572.
[5] Shanbhag A S, Bailey H O, Hwang, D S, et al. Quantita-tive analysis of ultrahigh molecular weight polyethylene
(UHMWPE) wear debris associated with total knee re-placements. Journal of Biomedical Materials Research,
2000, 53(1): 100110.
[6] Campbell P, Ma S, Yeom B, et al. Isolation of predomi-nantly submicron-sized UHMWPE wear particles fromperiprosthetic tissues. Journal of Biomedical MaterialsResearch, 1995, 29(1): 127131.
[7] Kobayashi A, Bonfield W, Kadova Y, et al. Size andshape of particulate polyethylene wear debris in total joint replacements. Proceedings of the Institution ofMechanical Engineers, 1997, 211(1): 1115.
[8] Goodman S B, Song Y, Yoo J Y, et al. Local infusion of
FGF-2 enhances bone in growth in rabbit chambers inthe presence of polyethylene particles. Journal of Bio-medical Materials Research, 2003, 65A(4): 454461.
[9] Roy S, Pal S. Characterization of silane coated hollowsphere alumina-reinforced ultra high molecular weight polyethylene composite as a possible bone substitutematerial.Bull Mater Sci, 2002, 25(7): 609612.
[10] Hashimoto M, Takadama H, Mizuno M, et al. Titaniumdioxide/ultra high molecular weight polyethylene com-
posite for bone-repairing applications: preparation andbiocompatibility. Key Engineering Materials, 2003(240/
242): 415418.[11] Xie X L, Tang C Y, Chan K Y, et al. Wear performance
of ultrahigh molecular weight polyethylene/quartz com-posites.Biomaterials, 2003, 24(11): 18891896.
[12] Tong J, Ma Y H, Jiang M. Effects of the wollastonitefiber modification on the sliding wear behavior of the
UHMWPE composites. Wear, 2003, 255(1/6): 734741.[13] Anderson B C, Bloom P D, Baikerikar K G, et al.
Al-Cu-Fe quasicrystal/ultra-high molecular weight poly-ethylene composites as biomaterials for acetabular cupp
8/4/2019 Biotribological Behavior of Ultra High Molecular Weight
7/7
Journal of China University of Mining & Technology Vol.18 No.4612
rosthetics.Biomaterials, 2002, 23(8): 17611768.[14] Hashmi S A R, Neogi S, Pandey A, et al. Sliding wear of
PP/UHMWPE blends: effect of blend composition. Wear,2001, 247(1): 914.
[15] Zhou J S, Feng F Y, Improvement of the tribologicalbehavior of ultra-high-molecular-weight polyethylene by
incorporation of poly (phenyl p-hydroxyzoate). Journalof Applied Polymer Science, 2005, 96(6): 23362343.
[16] Silva V V, Fernando Z, Lameiras C, et al. Microstruc-tural and mechanical study of zinconia-hydroxyapatite(ZH) composite ceramics for biomedical applications.Composites Science and Technology, 2001, 61(2): 301
310.[17] Reis R L, Granja P L, Cunha A M. Impact behavior of
UHMWPE/HA composites for orthopedic prostheses.Ottenbrite RM. Frontiers in Biomedical Polymer Appli-
cations. Lancaster: PA Technomic Publishing, 1998:251263.
[18] Cunha A M, Reis R L, Ferreira F G, et al. The influenceof processing conditions on the mechanical behavior of
UHMWPE/HA and PMMA/HA composites. Kossowsky
R, Kossowsky N. Chania. Greece: Netherlands: KluwerAcademic Publishers, 1994.
[19] Knets I V, Bunina L O, Filipenkov V V. Ultra-high-molecular weight polyethylene and hydroxylapa-
tite-based materials for replacement of bone tissue.Mekhanika Kompozitnykh Materialov, 1993, 29(2): 240250.
[20] Kalin M, Jahanmir S, Ives L K. Effefct of counterface
roughness on abrisive wear of hydroxyapatite. Wear,
2002, 252(910): 679685.
[21] Wang Q L, Ge S R, Zhang D K, Nano-mechanical prop-erties and biotribological behaviors of nanosized HA/
partially-stabilized zirconia composites. Wear, 2005, 259
(712): 952957.[22] Benson R S. Use of radiation in biomaterials science.
Nuclear Instruments and Methods in Physics Research
Section B: Beam Interactions with Materials and Atoms,2002, 191(14): 752757.
[23] Clarke I C, Chan F W, Essner A, et al. Multi-laboratorysimulator studies on effects of serum proteins on PTFE
cup wear. Wear, 2001, 250(112): 188198.[24] Wang A, Essner A, Polineni V K, et al. Lubrication and
wear of ultra-high molecular weight polyethylene in total joint replacements. Tribology International, 1998, 31 (1
3): 1733.[25] Ge S R, Wang Q L, Zhang D K, et al. Friction and wear
behavior of nitrogen ion implanted UHMWPE against
ZrO2 ceramic. Wear, 2003, 255(16): 10691075.
Top Related