The Experts below are selected from a list of 1950 Experts worldwide ranked by ideXlab platform
J Fisher - One of the best experts on this subject based on the ideXlab platform.
-
the influence of molecular weight crosslinking and Counterface roughness on tnf alpha production by macrophages in response to ultra high molecular weight polyethylene particles
Biomaterials, 2004Co-Authors: Joanne Ingram, J Fisher, M H Stone, Eileen InghamAbstract:The response of murine macrophages to clinically relevant polyethylene wear particles generated from different polyethylenes at various time points and volumetric doses in vitro was evaluated. Clinically relevant ultra high molecular weight polyethylene (UHMWPE) wear debris was generated in vitro in a lubricant of RPMI 1640 supplemented with 25% (v/v) foetal calf serum using a multi-directional pin-on-plate wear rig under sterile conditions. Wear debris was cultured with C3H murine peritoneal macrophages at various particle volume (microm(3)): cell number ratios. The secretion of TNF-alpha was determined by ELISA. Initially the effect of molecular weight of UHMWPE was considered. Higher molecular weight GUR415HP was shown to have a lower wear rate than the lower molecular weight GUR1120, however a greater volume of the wear debris produced by the high molecular weight GUR415HP was in the 0.1-1.0 microm size range. Wear debris from GUR415HP produced significant levels of TNF-alpha at a concentration of 1 microm(3)/cell while at least 10 microm(3)/cell of GUR1120 wear debris per cell was needed to produce significant levels of TNF-alpha. Secondly the effects of crosslinking GUR1050 was examined when worn against a scratched Counterface. The wear rate of the material was shown to decrease as the level of crosslinking increased. However the materials crosslinked with 5 and 10 Mrad of gamma irradiation produced higher percentages of 0.1-1.0 microm size wear particles than the non-crosslinked material. While the crosslinked material was able to stimulate cells to produce significantly elevated TNF-alpha levels at a particle concentration of just 0.1 microm(3)/cell only concentrations of 10 microm(3)/cell and above of the non-crosslinked wear debris were stimulatory. When the Counterface was changed from scratched to smooth the wear rate for all three GUR1050 materials was further reduced. For the first time nanometre size wear particles were observed from polyethylene which reduced the percentage mass of debris in the 0.1-1.0 microm size range. For all three materials on the smooth Counterface only concentrations of 50 microm(3)/cell and above were stimulatory. This study has demonstrated that molecular weight, crosslinking and Counterface roughness are important factors in determining the biological activity of polyethylene.
-
new materials for mobile bearing knee prosthesis titanium nitride Counterface coatings for reduction of polyethylene wear
2002Co-Authors: V C Jones, M H Stone, Daniel D Auger, J FisherAbstract:Wear of polyethylene is widely recognized as a cause of osteolysis and failure in artificial hip joints [2]. Recent studies of tissues surrounding knee prosthesis [1] have shown the accumulation of micron and sub micron size polyethylene wear debris, at similar levels to that found in the hip, hence indicating the potential for longer term osteolysis. In the hip damage or scratching to the femoral Counterface has been shown to accelerate polyethylene wear [6] and it is now recommended to use alumina ceramic femoral heads, which arc more damage resistant and can deliver lower long term wear rates [5]. Similar damage has been found in knees [4]. The complexity of the femoral and tibial tray geometries in the knee do not readily lend themselves for replacement of the metallic bearing Counterfaces with monolithic ceramic- materials. An alternative approach is to modify the polished metallic bearing surface with hard smooth ‘ceramic like’ coatings.
-
quantification of third body damage to the tibial Counterface in mobile bearing knees
Proceedings of the Institution of Mechanical Engineers Part H: Journal of Engineering in Medicine, 2001Co-Authors: V C Jones, M H Stone, D C Barton, Daniel D Auger, I R Williams, William R Walsh, J FisherAbstract:Fourteen pairs of explanted low contact stress (LCS) tibial interface components: six rotating platform (RP), six meniscal (MN) and two anterior-posterior (AP) glide designs, have been analysed with particular attention paid to the condition of the tibial Counterfaces. The average surface roughness, Ra, for the tibial trays ranged from 0.01 to 0.087 micron, significantly greater than the unworn control measurement of 0.008 micron. The scratch geometry analysis showed that the scratch peaks were found to be consistently of a lower aspect ratio than the scratch valleys and under 1 micron in height (average asperity height Rp = 0.52 micron, aspect ratio delta p = 0.01, average asperity depth Rv = 1.10 microns, delta v = 0.05). The largest scratches were 3-4 microns in both Rp and Rv. In vitro tests have shown that ultra-high molecular weight polyethylene (UHMWPE) wear increases in the presence of Counterface scratches perpendicular to the direction of motion. In these explants, the unidirectional motion produced scratches parallel to the direction of sliding which is predicted to produce a smaller increase in UHMWPE wear. Other designs in mobile bearing knees have less constrained motion at the tibial Counterface and this has been shown to accelerate wear; it may also lead to a further increase in wear in the presence of third body scratches. It may be possible in future knee designs to reduce this type of wear damage by introducing alternative materials or coatings which are more resistant to scratching and surface roughening.
-
comparative wear and wear debris under three different Counterface conditions of crosslinked and non crosslinked ultra high molecular weight polyethylene
Bio-medical Materials and Engineering, 2001Co-Authors: M M Endo, J Fisher, Eileen Ingham, D C Barton, P S M Barbour, J L Tipper, M H StoneAbstract:The wear debris generated from ultra high molecular weight polyethylene (UHMWPE) have been recognised as one of the major causes of failure in total hip replacements (THR). It is essential to reduce the wear debris generated from UHMWPE acetabular cups in order to minimise this problem. Debris in the submicron size range is believed to have greater osteolytic potential. It is now known that crosslinked UHMWPE acetabular cups have reduced volumetric wear rates but little is known about the influence of crosslinking on the size and morphology of the wear debris. In this study, the wear of grade GUR 1020 crosslinked (vacuum gamma irradiated), GUR 1120 crosslinked (acetylene enhanced irradiated) and non cross linked (ethylene oxide sterilised) GUR 1020 UHMWPE was compared in multidirectional pin-on-plate wear tests under three different Counterface conditions (smooth, isotropically rough and scratched Counterfaces). Multidirectional motion was chosen because this motion was closer to the relative motion in the natural hip. From this study, better wear resistance of crosslinked UHMWPE compared with non-crosslinked UHMWPE was demonstrated for the smooth Counterface conditions. However, in the rough and scratched Counterface conditions, the vacuum gamma irradiated crosslinked material produced significantly higher wear rates than the non-crosslinked material. The analysis of the wear debris showed that the majority of the volume of the acetylene enhanced crosslinked UHMWPE wear debris was in the most biologically active size range (0.1 to 0.5 microm). In contrast, the non-crosslinked material and the vacuum gamma irradiated crosslinked material had a greater proportion of the volume of the debris in the larger size ranges which are less biologically active. This has important implications for its osteolytic potential.
-
simulation of tibial Counterface wear in mobile bearing knees with uncoated and adlc coated surfaces
Bio-medical Materials and Engineering, 2001Co-Authors: V C Jones, M H Stone, D C Barton, Daniel D Auger, C Hardaker, J FisherAbstract:A multidirectional pin-on-plate reciprocating machine was used to compare the wear performance of UHMWPE sliding against cast cobalt chrome (CoCr) plates that were either untreated or coated with Amorphous Diamond Like Carbon (ADLC). The test conditions were based on a 1/5 scale model representative of in vivo motion at the tibial Counterfaces of unconstrained mobile bearing knees (1). The average STERR wear rates were 13.78 1.06 mm 3 /Mcycles for the ADLC Counterfaces and 0.504 0.12 mm 3 /Mcycles for the control CoCr Counterfaces. All of the pins run on the ADLC Counterfaces exhibited the same patterns of blistering along the central axis, and severe abrasion elsewhere to the extent that all of the original machining marks were removed after just one week of testing. The average value of friction coefficient was 0.24 for the ADLC Counterfaces and 0.073 for the control CoCr Counterfaces. The factor of 3.5 increase was statistically significant at p< 0:05. In the tribological evaluation of ADLC coatings for tibial trays in mobile bearing knees, this study shows that this specific Physical Vapour Deposition (PVD) ADLC showed significantly poorer frictional and wear performance than uncoated surfaces which was sufficient to negate any potential benefits of improved resistance to third body damage.
M H Stone - One of the best experts on this subject based on the ideXlab platform.
-
the influence of molecular weight crosslinking and Counterface roughness on tnf alpha production by macrophages in response to ultra high molecular weight polyethylene particles
Biomaterials, 2004Co-Authors: Joanne Ingram, J Fisher, M H Stone, Eileen InghamAbstract:The response of murine macrophages to clinically relevant polyethylene wear particles generated from different polyethylenes at various time points and volumetric doses in vitro was evaluated. Clinically relevant ultra high molecular weight polyethylene (UHMWPE) wear debris was generated in vitro in a lubricant of RPMI 1640 supplemented with 25% (v/v) foetal calf serum using a multi-directional pin-on-plate wear rig under sterile conditions. Wear debris was cultured with C3H murine peritoneal macrophages at various particle volume (microm(3)): cell number ratios. The secretion of TNF-alpha was determined by ELISA. Initially the effect of molecular weight of UHMWPE was considered. Higher molecular weight GUR415HP was shown to have a lower wear rate than the lower molecular weight GUR1120, however a greater volume of the wear debris produced by the high molecular weight GUR415HP was in the 0.1-1.0 microm size range. Wear debris from GUR415HP produced significant levels of TNF-alpha at a concentration of 1 microm(3)/cell while at least 10 microm(3)/cell of GUR1120 wear debris per cell was needed to produce significant levels of TNF-alpha. Secondly the effects of crosslinking GUR1050 was examined when worn against a scratched Counterface. The wear rate of the material was shown to decrease as the level of crosslinking increased. However the materials crosslinked with 5 and 10 Mrad of gamma irradiation produced higher percentages of 0.1-1.0 microm size wear particles than the non-crosslinked material. While the crosslinked material was able to stimulate cells to produce significantly elevated TNF-alpha levels at a particle concentration of just 0.1 microm(3)/cell only concentrations of 10 microm(3)/cell and above of the non-crosslinked wear debris were stimulatory. When the Counterface was changed from scratched to smooth the wear rate for all three GUR1050 materials was further reduced. For the first time nanometre size wear particles were observed from polyethylene which reduced the percentage mass of debris in the 0.1-1.0 microm size range. For all three materials on the smooth Counterface only concentrations of 50 microm(3)/cell and above were stimulatory. This study has demonstrated that molecular weight, crosslinking and Counterface roughness are important factors in determining the biological activity of polyethylene.
-
new materials for mobile bearing knee prosthesis titanium nitride Counterface coatings for reduction of polyethylene wear
2002Co-Authors: V C Jones, M H Stone, Daniel D Auger, J FisherAbstract:Wear of polyethylene is widely recognized as a cause of osteolysis and failure in artificial hip joints [2]. Recent studies of tissues surrounding knee prosthesis [1] have shown the accumulation of micron and sub micron size polyethylene wear debris, at similar levels to that found in the hip, hence indicating the potential for longer term osteolysis. In the hip damage or scratching to the femoral Counterface has been shown to accelerate polyethylene wear [6] and it is now recommended to use alumina ceramic femoral heads, which arc more damage resistant and can deliver lower long term wear rates [5]. Similar damage has been found in knees [4]. The complexity of the femoral and tibial tray geometries in the knee do not readily lend themselves for replacement of the metallic bearing Counterfaces with monolithic ceramic- materials. An alternative approach is to modify the polished metallic bearing surface with hard smooth ‘ceramic like’ coatings.
-
quantification of third body damage to the tibial Counterface in mobile bearing knees
Proceedings of the Institution of Mechanical Engineers Part H: Journal of Engineering in Medicine, 2001Co-Authors: V C Jones, M H Stone, D C Barton, Daniel D Auger, I R Williams, William R Walsh, J FisherAbstract:Fourteen pairs of explanted low contact stress (LCS) tibial interface components: six rotating platform (RP), six meniscal (MN) and two anterior-posterior (AP) glide designs, have been analysed with particular attention paid to the condition of the tibial Counterfaces. The average surface roughness, Ra, for the tibial trays ranged from 0.01 to 0.087 micron, significantly greater than the unworn control measurement of 0.008 micron. The scratch geometry analysis showed that the scratch peaks were found to be consistently of a lower aspect ratio than the scratch valleys and under 1 micron in height (average asperity height Rp = 0.52 micron, aspect ratio delta p = 0.01, average asperity depth Rv = 1.10 microns, delta v = 0.05). The largest scratches were 3-4 microns in both Rp and Rv. In vitro tests have shown that ultra-high molecular weight polyethylene (UHMWPE) wear increases in the presence of Counterface scratches perpendicular to the direction of motion. In these explants, the unidirectional motion produced scratches parallel to the direction of sliding which is predicted to produce a smaller increase in UHMWPE wear. Other designs in mobile bearing knees have less constrained motion at the tibial Counterface and this has been shown to accelerate wear; it may also lead to a further increase in wear in the presence of third body scratches. It may be possible in future knee designs to reduce this type of wear damage by introducing alternative materials or coatings which are more resistant to scratching and surface roughening.
-
comparative wear and wear debris under three different Counterface conditions of crosslinked and non crosslinked ultra high molecular weight polyethylene
Bio-medical Materials and Engineering, 2001Co-Authors: M M Endo, J Fisher, Eileen Ingham, D C Barton, P S M Barbour, J L Tipper, M H StoneAbstract:The wear debris generated from ultra high molecular weight polyethylene (UHMWPE) have been recognised as one of the major causes of failure in total hip replacements (THR). It is essential to reduce the wear debris generated from UHMWPE acetabular cups in order to minimise this problem. Debris in the submicron size range is believed to have greater osteolytic potential. It is now known that crosslinked UHMWPE acetabular cups have reduced volumetric wear rates but little is known about the influence of crosslinking on the size and morphology of the wear debris. In this study, the wear of grade GUR 1020 crosslinked (vacuum gamma irradiated), GUR 1120 crosslinked (acetylene enhanced irradiated) and non cross linked (ethylene oxide sterilised) GUR 1020 UHMWPE was compared in multidirectional pin-on-plate wear tests under three different Counterface conditions (smooth, isotropically rough and scratched Counterfaces). Multidirectional motion was chosen because this motion was closer to the relative motion in the natural hip. From this study, better wear resistance of crosslinked UHMWPE compared with non-crosslinked UHMWPE was demonstrated for the smooth Counterface conditions. However, in the rough and scratched Counterface conditions, the vacuum gamma irradiated crosslinked material produced significantly higher wear rates than the non-crosslinked material. The analysis of the wear debris showed that the majority of the volume of the acetylene enhanced crosslinked UHMWPE wear debris was in the most biologically active size range (0.1 to 0.5 microm). In contrast, the non-crosslinked material and the vacuum gamma irradiated crosslinked material had a greater proportion of the volume of the debris in the larger size ranges which are less biologically active. This has important implications for its osteolytic potential.
-
simulation of tibial Counterface wear in mobile bearing knees with uncoated and adlc coated surfaces
Bio-medical Materials and Engineering, 2001Co-Authors: V C Jones, M H Stone, D C Barton, Daniel D Auger, C Hardaker, J FisherAbstract:A multidirectional pin-on-plate reciprocating machine was used to compare the wear performance of UHMWPE sliding against cast cobalt chrome (CoCr) plates that were either untreated or coated with Amorphous Diamond Like Carbon (ADLC). The test conditions were based on a 1/5 scale model representative of in vivo motion at the tibial Counterfaces of unconstrained mobile bearing knees (1). The average STERR wear rates were 13.78 1.06 mm 3 /Mcycles for the ADLC Counterfaces and 0.504 0.12 mm 3 /Mcycles for the control CoCr Counterfaces. All of the pins run on the ADLC Counterfaces exhibited the same patterns of blistering along the central axis, and severe abrasion elsewhere to the extent that all of the original machining marks were removed after just one week of testing. The average value of friction coefficient was 0.24 for the ADLC Counterfaces and 0.073 for the control CoCr Counterfaces. The factor of 3.5 increase was statistically significant at p< 0:05. In the tribological evaluation of ADLC coatings for tibial trays in mobile bearing knees, this study shows that this specific Physical Vapour Deposition (PVD) ADLC showed significantly poorer frictional and wear performance than uncoated surfaces which was sufficient to negate any potential benefits of improved resistance to third body damage.
Eileen Ingham - One of the best experts on this subject based on the ideXlab platform.
-
the influence of molecular weight crosslinking and Counterface roughness on tnf alpha production by macrophages in response to ultra high molecular weight polyethylene particles
Biomaterials, 2004Co-Authors: Joanne Ingram, J Fisher, M H Stone, Eileen InghamAbstract:The response of murine macrophages to clinically relevant polyethylene wear particles generated from different polyethylenes at various time points and volumetric doses in vitro was evaluated. Clinically relevant ultra high molecular weight polyethylene (UHMWPE) wear debris was generated in vitro in a lubricant of RPMI 1640 supplemented with 25% (v/v) foetal calf serum using a multi-directional pin-on-plate wear rig under sterile conditions. Wear debris was cultured with C3H murine peritoneal macrophages at various particle volume (microm(3)): cell number ratios. The secretion of TNF-alpha was determined by ELISA. Initially the effect of molecular weight of UHMWPE was considered. Higher molecular weight GUR415HP was shown to have a lower wear rate than the lower molecular weight GUR1120, however a greater volume of the wear debris produced by the high molecular weight GUR415HP was in the 0.1-1.0 microm size range. Wear debris from GUR415HP produced significant levels of TNF-alpha at a concentration of 1 microm(3)/cell while at least 10 microm(3)/cell of GUR1120 wear debris per cell was needed to produce significant levels of TNF-alpha. Secondly the effects of crosslinking GUR1050 was examined when worn against a scratched Counterface. The wear rate of the material was shown to decrease as the level of crosslinking increased. However the materials crosslinked with 5 and 10 Mrad of gamma irradiation produced higher percentages of 0.1-1.0 microm size wear particles than the non-crosslinked material. While the crosslinked material was able to stimulate cells to produce significantly elevated TNF-alpha levels at a particle concentration of just 0.1 microm(3)/cell only concentrations of 10 microm(3)/cell and above of the non-crosslinked wear debris were stimulatory. When the Counterface was changed from scratched to smooth the wear rate for all three GUR1050 materials was further reduced. For the first time nanometre size wear particles were observed from polyethylene which reduced the percentage mass of debris in the 0.1-1.0 microm size range. For all three materials on the smooth Counterface only concentrations of 50 microm(3)/cell and above were stimulatory. This study has demonstrated that molecular weight, crosslinking and Counterface roughness are important factors in determining the biological activity of polyethylene.
-
comparative wear and wear debris under three different Counterface conditions of crosslinked and non crosslinked ultra high molecular weight polyethylene
Bio-medical Materials and Engineering, 2001Co-Authors: M M Endo, J Fisher, Eileen Ingham, D C Barton, P S M Barbour, J L Tipper, M H StoneAbstract:The wear debris generated from ultra high molecular weight polyethylene (UHMWPE) have been recognised as one of the major causes of failure in total hip replacements (THR). It is essential to reduce the wear debris generated from UHMWPE acetabular cups in order to minimise this problem. Debris in the submicron size range is believed to have greater osteolytic potential. It is now known that crosslinked UHMWPE acetabular cups have reduced volumetric wear rates but little is known about the influence of crosslinking on the size and morphology of the wear debris. In this study, the wear of grade GUR 1020 crosslinked (vacuum gamma irradiated), GUR 1120 crosslinked (acetylene enhanced irradiated) and non cross linked (ethylene oxide sterilised) GUR 1020 UHMWPE was compared in multidirectional pin-on-plate wear tests under three different Counterface conditions (smooth, isotropically rough and scratched Counterfaces). Multidirectional motion was chosen because this motion was closer to the relative motion in the natural hip. From this study, better wear resistance of crosslinked UHMWPE compared with non-crosslinked UHMWPE was demonstrated for the smooth Counterface conditions. However, in the rough and scratched Counterface conditions, the vacuum gamma irradiated crosslinked material produced significantly higher wear rates than the non-crosslinked material. The analysis of the wear debris showed that the majority of the volume of the acetylene enhanced crosslinked UHMWPE wear debris was in the most biologically active size range (0.1 to 0.5 microm). In contrast, the non-crosslinked material and the vacuum gamma irradiated crosslinked material had a greater proportion of the volume of the debris in the larger size ranges which are less biologically active. This has important implications for its osteolytic potential.
-
a study of the combined effects of shelf ageing following irradiation in air and Counterface roughness on the wear of uhmwpe
Bio-medical Materials and Engineering, 1997Co-Authors: A A Besong, J L Hailey, Eileen Ingham, M H Stone, B M Wroblewski, J FisherAbstract:Damage to polished femoral heads in vivo can cause increased wear of acetabular cups. Oxidation and ageing after sterilisation by gamma irradiation in air, can also change the mechanical properties and wear resistance of ultra high molecular weight polyethylene (UHMWPE). This study investigated the combined effect of these changes in material properties on the wear of UHMWPE for different Counterface roughnesses, representative of new femoral heads and those damaged in vivo. Wear rates were studied on a tri-pin-on-disc tribometer in a protein-containing solution. A comparison was made of the wear, using three different Counterface roughnesses, of specimens that were manufactured from polyethylene acetabular cups of different shelf ages (3-120 months) after gamma irradiation in air but never implanted. These were compared to the wear of control specimens that were manufactured from cups that had not been sterilised. The wear surfaces were tested 1 mm below the initial articulating surface of the cup, the position of high degradation. The wear rate of UHMWPE which had been sterilised by gamma irradiation in air was shown to increase significantly with ageing time on the shelf for all Counterface conditions. The wear rate of all materials increased markedly as the Counterface roughness increased, but to different extents depending on the age of the material. The combined effect of ageing and increase in Counterface roughness had a dramatic effect (as high as 2000 fold increase) on the wear rate. Both ageing of the polymer and damage to the femoral head have been cited as causing increased wear in vivo. The results of this study demonstrate that these variables can act synergistically to markedly effect UHMWPE wear rate.
-
ultra high molecular weight polyethylene wear debris generated in vivo and in laboratory tests the influence of Counterface roughness
Proceedings of the Institution of Mechanical Engineers Part H: Journal of Engineering in Medicine, 1996Co-Authors: J L Hailey, Eileen Ingham, M H Stone, B M Wroblewski, J FisherAbstract:The objective of this study was to investigate the effect of Counterface roughness and lubricant on the morphology of ultra-high molecular weight polyethylene (UHMWPE) wear debris generated in laboratory wear tests, and to compare this with debris isolated from explanted tissue. Laboratory tests used UHMWPE pins sliding against stainless steel Counterfaces. Both water and serum lubricants were used in conjunction with rough and smooth Counterfaces. The lubricants and tissue from revision hip surgery were processed to digest the proteins and permit filtration. This involved denaturing the proteins with potassium hydroxide (KOH), sedimentation of any remaining proteins, and further digestion of these proteins with chromic acid. All fractions were then passed through a 0.2 micron membrane, and the debris examined using scanning electron microscopy. The laboratory studies showed that the major variable influencing debris morphology was Counterface roughness. The rougher Counterfaces produced larger numbers of smaller particles, with a size range extending below 1 micron. For smooth Counterfaces there were fewer of these small particles, and evidence of larger platelets, greater than 10 microns in diameter. Analysis of the debris from explanted tissues showed a wide variation in the particle size distribution, ranging from below 1 micron up to several millimetres in size. Of major clinical significance in relation to osteolysis and loosening is roughening of the femoral components, which may lead to greater numbers of the sub-micron-sized particles.
Judith A Harrison - One of the best experts on this subject based on the ideXlab platform.
-
molecular scale tribology of amorphous carbon coatings effects of film thickness adhesion and long range interactions
Journal of the American Chemical Society, 2002Co-Authors: Paul T Mikulski, Judith A HarrisonAbstract:Classical molecular dynamics simulations have been conducted to investigate the atomic-scale friction and wear when hydrogen-terminated diamond (111) Counterfaces are in sliding contact with diamond (111) surfaces coated with amorphous, hydrogen-free carbon films. Two films, with approximately the same ratio of sp3-to-sp2 carbon, but different thicknesses, have been examined. Both systems give a similar average friction in the load range examined. Above a critical load, a series of tribochemical reactions occur resulting in a significant restructuring of the film. This restructuring is analogous to the “run-in” observed in macroscopic friction experiments and reduces the friction. The contribution of adhesion between the probe (Counterface) and the sample to friction was examined by varying the saturation of the Counterface. Decreasing the degree of Counterface saturation, by reducing the hydrogen termination, increases the friction. Finally, the contribution of long-range interactions to friction was exa...
-
molecular scale tribology of amorphous carbon coatings effects of film thickness adhesion and long range interactions
Journal of the American Chemical Society, 2002Co-Authors: Guangtu Gao, Paul T Mikulski, Judith A HarrisonAbstract:Classical molecular dynamics simulations have been conducted to investigate the atomic-scale friction and wear when hydrogen-terminated diamond (111) Counterfaces are in sliding contact with diamond (111) surfaces coated with amorphous, hydrogen-free carbon films. Two films, with approximately the same ratio of sp(3)-to-sp(2) carbon, but different thicknesses, have been examined. Both systems give a similar average friction in the load range examined. Above a critical load, a series of tribochemical reactions occur resulting in a significant restructuring of the film. This restructuring is analogous to the "run-in" observed in macroscopic friction experiments and reduces the friction. The contribution of adhesion between the probe (Counterface) and the sample to friction was examined by varying the saturation of the Counterface. Decreasing the degree of Counterface saturation, by reducing the hydrogen termination, increases the friction. Finally, the contribution of long-range interactions to friction was examined by using two potential energy functions that differ only in their long-range forces to examine friction in the same system.
Surya K Mallapragada - One of the best experts on this subject based on the ideXlab platform.
-
al cu fe quasicrystal ultra high molecular weight polyethylene composites as biomaterials for acetabular cup prosthetics
Biomaterials, 2002Co-Authors: Brian C Anderson, Paul D Bloom, K G Baikerikar, Valerie V Sheares, Surya K MallapragadaAbstract:Abstract Polymer composites of Al–Cu–Fe quasicrystals and ultra-high molecular weight polyethylene (UHMWPE) were investigated for use in acetabular cup prosthetics. The wear properties of the Al–Cu–Fe/UHMWPE samples and a 440 steel ball Counterface were measured. The mechanical strength of the Al–Cu–Fe/UHMWPE composites was compared to UHMWPE and alumina/UHMWPE. The biocompatibility of the composite material was tested using a direct contact cytotoxicity assay. Al–Cu–Fe/UHMWPE demonstrated lower volume loss after wear and higher mechanical strength than UHMWPE. This composite material also showed no increase in Counterface wear or cytotoxicity relative to UHMWPE. These combined results demonstrate that Al–Cu–Fe/UHMWPE composites are promising candidate materials for acetabular cup prosthetics.
