Wear Of Ultra-high Molecular Weight Polyethylene Research Articles

The effect of ultra-high molecular weight polyethylene wear debris on MG63 osteosarcoma cells in vitro.

Focal osteolysis due to ultra-high molecular weight polyethylene wear debris involves effects on both bone resorption and bone formation. The response of MG63 osteoblast-like osteosarcoma cells to ultra-high molecular weight polyethylene wear debris isolated by enzymatic digestion of granulomatous tissue obtained from the sites of failed total hip arthroplasties was examined. Scanning electron microscopy, particle-size analysis, and Fourier transform infrared spectroscopy were used to characterize the number, morphology, size distribution, and chemical composition of the particles. Cell response was assessed by adding particles at varying dilutions to confluent cultures and measuring changes in cell proliferation (number of cells and [3H]-thymidine incorporation), osteoblast function (alkaline-phosphatase-specific activity and osteocalcin production), matrix production (collagen production and proteoglycan sulfation), and local cytokine production (prostaglandin-E2 production). The mean size of the particles was 0.60 micrometer, and 95 percent of the particles had a size of less than 1.5 micrometers. The number of particles per gram of tissue ranged from 1.39 to 3.38x10(9). Three of the four batches of particles were endotoxin-free. Exposure of the cells to particles of wear debris significantly increased the number of cells (p<0.05) and the [3H]-thymidine incorporation (p<0.05) in a dose-dependent manner. In contrast, the addition of particles decreased alkaline-phosphatase-specific activity and osteocalcin production. Collagen production and proteoglycan sulfation were also decreased, while prostaglandin-E2 synthesis was increased by the addition of particles. Ultra-high molecular weight polyethylene particles isolated from human tissue stimulated osteoblast proliferation and prostaglandin-E2 production and inhibited cell differentiation and matrix production. These results indicate that particles of wear debris inhibit cell functions associated with bone formation and that osteoblasts may produce factors in response to wear debris that influence neighboring cells, such as osteoclasts and macrophages. Particles of wear debris, especially ultra-high molecular weight polyethylene, have been implicated in the loosening of implants and the development of osteolysis. The present study shows that particles of ultra-high molecular weight polyethylene isolated from human tissue inhibit osteoblast functions associated with bone formation. In addition, particles of wear debris induced osteoblasts to secrete factors capable of influencing neighboring cells, such as osteoclasts and macrophages. These results suggest that osteoblasts may play a role in the cascade of events leading to granuloma formation, osteolysis, and failure of orthopaedic implants.

The influence of lubricant on the morphology of ultra-high molecular weight polyethylene wear debris generated in laboratory tests.

Since the implication of polyethylene wear debris as a major cause of osteolysis in total joint replacements, there has been much interest in polyethylene wear studies and in cell culture studies using ultra-high molecular weight polyethylene (UHMWPE) wear debris. Studies have shown that particles in the 0.1-10 microns size range are particularly important in causing adverse cellular reactions resulting in osteolysis. The morphology, the mass and size distributions, and the number of wear particles produced at the joint surfaces are influenced by the tribological conditions at the joint. Laboratory wear tests are used to investigate the wear properties of prosthetic joint materials and different research groups have used different lubricants in these tests. This paper shows that the volumetric wear and morphology of UHMWPE particles generated in vitro are influenced by the type of lubricant used. This study compared, quantitatively, UHMWPE wear debris generated in deionized water to debris that was generated in a system lubricated by bovine serum which was diluted to 25 per cent. The wear factors of UHMWPE in water and serum lubricants were significantly different (p < 0.05). UHMWPE wore 14 times more in water than in serum. Quantitative analysis of the wear particles showed that the debris that was generated in serum was morphologically different from debris that was produced in a water-lubricated system. Furthermore, the particles produced in serum showed a closer similarity to those found in retrieved acetabular tissues.

Morphology of In Vitro generated ultrahigh molecular weight polyethylene wear particles as a function of contact conditions and material parameters

Osteolysis in total joint replacements has been linked to ultrahigh molecular weight polyethylene (UHMWPE) wear particles. Although the biological response to these UHMWPE particles is poorly understood at present, it has been demonstrated that particle size and morphology are important factors in such a response. The goal of the present study was twofold: to develop a comprehensive set of particle size and shape descriptors, and to use these descriptors to analyze the effects of different contact conditions and material parameters during the wear process on the size and morphology of UHMWPE wear debris. The three parameters studied were average contact stress (6.9 and 13.8 MPa), macromolecular orientation of the UHMWPE with respect to the wear direction (0°, 45°, and 90°), and UHMWPE initial surface roughness (Ra = 1 and 3 μm). Tests were performed using pin on disk or cylinder on plate systems for 3 million cycles each. The results indicated that the initial surface roughness of the UHMWPE test samples had no effect on the morphology of UHMWPE wear particles. However, particle size and morphology were a function of the average contact stress and molecular orientation of the UHMWPE. © 1999 John Wiley & Sons, Inc. J Biomed Mater Res (Appl Biomater) 48: 61–69, 1999

Morphology ofIn Vitro generated ultrahigh molecular weight polyethylene wear particles as a function of contact conditions and material parameters

Osteolysis in total joint replacements has been linked to ultrahigh molecular weight polyethylene (UHMWPE) wear particles. Although the biological response to these UHMWPE particles is poorly understood at present, it has been demonstrated that particle size and morphology are important factors in such a response. The goal of the present study was twofold: to develop a comprehensive set of particle size and shape descriptors, and to use these descriptors to analyze the effects of different contact conditions and material parameters during the wear process on the size and morphology of UHMWPE wear debris. The three parameters studied were average contact stress (6.9 and 13.8 MPa), macromolecular orientation of the UHMWPE with respect to the wear direction (0 degrees , 45 degrees , and 90 degrees ), and UHMWPE initial surface roughness (Ra = 1 and 3 microm). Tests were performed using pin on disk or cylinder on plate systems for 3 million cycles each. The results indicated that the initial surface roughness of the UHMWPE test samples had no effect on the morphology of UHMWPE wear particles. However, particle size and morphology were a function of the average contact stress and molecular orientation of the UHMWPE.

Ultrahigh molecular weight polyethylene particles have direct effects on proliferation, differentiation, and local factor production of MG63 osteoblast-like cells.

Small particles of ultrahigh molecular weight polyethylene stimulate formation of foreign-body granulomas and bone resorption. Bone formation may also be affected by wear debris. To determine if wear debris directly affects osteoblasts, we characterized a commercial preparation of ultrahigh molecular weight polyethylene (GUR4150) particles and examined their effect on MG63 osteoblast-like cells. In aliquots of the culture medium containing ultrahigh molecular weight polyethylene, 79% of the particles were less than 1 microm in diameter, indicating that the cells were exposed to particles of less than 1 microm. MG63 cell response to the particles was measured by assaying cell number, [3H]thymidine incorporation, alkaline phosphatase specific activity, osteocalcin production, [35S]sulfate incorporation, and production of prostaglandin E2 and transforming growth factor-beta. Cell number and [3H]thymidine incorporation were increased in a dose-dependent manner. Alkaline phosphatase specific activity, a marker of cell differentiation for the cultures, was significantly decreased, but osteocalcin production was not affected. [35S]sulfate incorporation, a measure of extracellular matrix production, was reduced. Prostaglandin E2 release was increased, but transforming growth factor-beta production was decreased in a dose-dependent manner. This shows that ultrahigh molecular weight polyethylene particles affect MG63 proliferation, differentiation, extracellular matrix synthesis, and local factor production. These effects were direct and dose dependent. The findings suggest that ultrahigh molecular weight polyethylene wear debris particles with an average size of approximately 1 microm may inhibit bone formation by inhibiting cell differentiation and reducing transforming growth factor-beta production and matrix synthesis. In addition, increases in prostaglandin E2 production may not only affect osteoblasts by an autocrine pathway but may also stimulate the proliferation and activation of cells in the monocytic lineage. These changes favor decreased bone formation and increased bone resorption as occur in osteolysis.

Effect of femoral head surface roughness on the wear of ultrahigh molecular weight polyethylene acetabular cups

We studied the effect of femoral head surface roughness on the wear of ultrahigh molecular weight polyethylene (UHMWPE) acetabular cups using a hip joint simulator and a reciprocating wear tester. Compared with the hip simulator, the reciprocating wear tester severely exaggerates the effect of counterface roughness on UHMWPE wear and drastically underestimates the wear rate of the UHMWPE against smooth undamaged counterfaces. According to the hip simulator test results, the wear rate of the UHMWPE cups is approximately proportional to the square root of the femoral head roughness R a (center-line-average roughness) rather than to R a raised to a power greater than one as predicted by pin-on-disk studies. Roughening of the femoral heads by an order of magnitude results in a 2- to 3-fold increase in the wear rate. Therefore, the much wider clinical variations of wear cannot be fully explained by variations in surface roughness of the femoral heads.

Quantification of third-body damage and its effect on UHMWPE wear with different types of femoral head.

We examined stainless-steel, cobalt-chrome, titanium and alumina and zirconia ceramic femoral heads retrieved at revision surgery. All the heads had articulated against ultra-high-molecular-weight-polyethylene (UHMWPE) acetabular cups. We studied the simulation of third-body damage and the wear of UHMWPE against the various materials used for the heads. The surfaces of the retrieved heads were analysed using a two-dimensional contacting profilometer. Third-body damage was characterised by the mean height of the scratches above the mean line (Rpm). The alumina ceramic and zirconia ceramic retrieved heads were found to have significantly less damage. In laboratory studies the ceramics were also more resistant to simulated third-body damage than the metal alloys. We studied the wear of UHMWPE against the damaged counterfaces in simple configuration tests. The damaged ceramics produced less polyethylene wear than the damaged metal counterfaces. The wear factor of UHMWPE against the damaged materials was dependent on the amount of damage to the counterface (Rp). Our study has shown the benefit of using the harder and more damage-resistant ceramic materials for femoral heads.

Quantification of third-body damage and its effect on UHMWPE wear with different types of femoral head

We examined stainless-steel, cobalt-chrome, titanium and alumina and zirconia ceramic femoral heads retrieved at revision surgery. All the heads had articulated against ultra-high-molecular-weight-polyethylene (UHMWPE) acetabular cups. We studied the simulation of third-body damage and the wear of UHMWPE against the various materials used for the heads. The surfaces of the retrieved heads were analysed using a two-dimensional contacting profilometer. Third-body damage was characterised by the mean height of the scratches above the mean line (Rpm). The alumina ceramic and zirconia ceramic retrieved heads were found to have significantly less damage. In laboratory studies the ceramics were also more resistant to simulated third-body damage than the metal alloys. We studied the wear of UHMWPE against the damaged counterfaces in simple configuration tests. The damaged ceramics produced less polyethylene wear than the damaged metal counterfaces. The wear factor of UHMWPE against the damaged materials was dependent on the amount of damage to the counterface (Rp). Our study has shown the benefit of using the harder and more damage-resistant ceramic materials for femoral heads.

Effect of cross-linking on the wear beha vior of ultra high molecular weight polyethylene (UHMWPE) used in total joint replacements

INTRODUCTION The major problem in total joint replacements remains to bc the wear debris induced peri-prosthetic osteolysis (mostly from UHMWPE components) that leads to aseptic loosening. Recently, cross-linking was shown to reduce the adhesive wear of UHMWPE under bovine serum lubrication. In this study, we investigated the prop&es of radiation crosslinked IJHMWPE as a function of cross-link density using the following two methods of irradiation: (i) irradiation at room temperature with subsequent melt-annealing (Method A) and (ii) irradiation with in-situ phase transformation (Method B). METHODS Bi-Directional pin-on-disk (POD) testing up to 2 million cycles with a Paul physiologic loading (peak load = 750 lb.) curve was used to determine the wear behavior as a function of cross-link density. The mechanical properties, thermal properties, density and surface oxidation was also determined. The cross-link density and molecular weight between cross-links was determined using equilibrium volume swelling. RESULTS The physical properties of the cross-linked UHMWPE varied significantly between the two methods used. At equal dose levels. the Method B always yielded far better mechanical properties than Method A. While the yield strength, ultimate tensile strength, density, and crystallinity decreased with increasing radiation dose, the wear resistance of the cross-linked polymer increased dramatically following both methods. DISCUSSION The inserted figure shows the wear behavior of UHMWPE as a function of radiation dose for both methods. The wear rate of the cross-linked polymer followed a transition from high wear to negligibly low wear. The transition to undetectable wear occurted at around absorbed radiation dose of 150 kGy for both methods, above which dose the pins tested on the POD did not show any sign of wear. In fact the original machining marks were still present after 2 million cycles of bi-directional loading. The method B which leads to minimum changes in material properties with dramatic improvement in the wear resistance of UHMWPE promises to be a preferable method of cross-linking IJHMWPE for applications in total joint arthroplasty as bearing surfaces.

The association between rates of wear in retrieved acetabular components and the radius of the femoral head.

Current evidence suggests that loosening of the acetabular socket is related to the volume of ultra-high molecular weight polyethylene wear debris generated at the articulating surfaces, through a process of bone resorption. Therefore it is important that the rate of volumetric wear is minimized in an attempt to extend the useful life of the procedure. Laboratory evidence indicates that a reduction in sliding distance would be beneficial in achieving this target and may be attained by a reduction in femoral head radius. To investigate the relationship between femoral head size and the rates of both volumetric wear and penetration, 200 acetabular components were retrieved at the time of revision surgery. The joints had femoral heads ranging in size from 11.1 to 19.8 mm radius. For those sockets that were loose at revision surgery, a significant correlation was observed, between the rate of volumetric wear and the radius of the femoral head. For this cohort an increase in radius of 1 mm resulted in an increased rate of volumetric wear of 5.1 (SE 1.4) mm3/yr. However, the explained variance in the regression was low and exemplifies the multifactorial nature of the wear process. In particular, it is anticipated that the activity of the patient will have a significant effect on the rate at which the debris is produced. No significant correlation was observed between the rate of linear wear and femoral head radius. These results would indicate a benefit in using head sizes of a smaller radius, which generate debris at a reduced rate, and therefore require more time to accumulate large volumes of wear products.

Effect of synovia constituents on friction and wear of ultra-high molecular weight polyethylene sliding against prosthetic joint materials

The effect of synovia constituents, such as a serum protein and hyaluronic acid, on the friction and wear of ultra-high molecular weight polyethylene (UHMWPE) was examined in a pin-on-disk test apparatus. In this study, UHMWPE pin specimens were articulated against stainless steel (SUS316) and alumina ceramic disk specimens. Both saline and diluted bovine serum were used as lubricants. Albumin, a kind of serum protein, and sodium hyaluronate were added to the saline respectively to identify their effects on the friction and wear of UHMWPE. As a result, each of the synovia constituents had a different influence on the friction and wear of UHMWPE. The wear rate in the albumin solution was not so different from that in the diluted serum, but friction coefficient was higher and the morphology of the wear surfaces observed by scanning electron microscope was quite different. On the other hand, hyaluronic acid could reduce the friction and wear of UHMWPE.

Wear of ultra-high molecular weight polyethylene against damaged and undamaged stainless steel and diamond-like carbon-coated counterfaces.

The wear of ultra-high molecular weight polyethylene (UHMWPE) in artificial joints and the resulting wear debris-induced osteolysis remains a major clinical concern in the orthopaedic sector. Third-body damage of metallic femoral heads is often cited as a cause of accelerated polyethylene wear, and the use of ceramic femoral heads in the hip is gaining increasing favour. In the knee prostheses and for smaller diameter femoral heads, the application of hard surface coatings, such as diamond-like carbon, is receiving considerable attention. However, to date, there has been little or no investigation of the tribology of these coatings in simulated biological environments. In this study, diamond-like carbon (DLC) has been compared to stainless steel in its undamaged form and following simulated third-body damage. The wear of UHMWPE was found to be similar when sliding against undamaged DLC and stainless steel counterfaces. DLC was found to be much more damage resistant than DLC. Under test conditions that simulate third-body damage to the femoral head, the wear of UHMWPE was seven times lower against DLC than against stainless steel (P < 0.05). The study shows DLC has considerable potential as a femoral bearing surface in artificial joints.

Effects of Particles on Fibroblast Proliferation and Bone Resorption In Vitro

An in vitro study was conducted to determine the ability of particle challenged human peripheral monocytes to modulate fibroblast proliferation and bone resorption. The effects of commercially pure titanium, titanium-aluminum-vanadium, and ultrahigh molecular weight polyethylene wear debris, either fabricated or retrieved from patients with failed total hip arthroplasties, were examined as a function of the composition, size, and dose of particles. In vitro generated particles were selected to be matched closely in particle size distribution to that found in vivo. Dosages were controlled by standardizing the ratio of particle surface area to mean monocyte surface area. The results support the hypothesis that, in vitro, challenge of monocytes by particulate wear debris results in a biphasic dose response. For the metal particles, fibrogenesis was observed over the range of 1x to 10x surface area ratio (the surface area of particles to the surface area of cells), although for metallic and polyethylene particles, saturated doses of 10x surface area ratio were required to stimulate bone resorption. In addition, metallic particles were able to stimulate fibrogenesis at doses at which simulated and retrieved polyethylene were ineffective. Although there may be a nonosteolytic chronically tolerable annual dose of ultrahigh molecular weight polyethylene wear debris corresponding to approximately 1x surface area ratio, lower doses, especially of metallic debris, may produce reactive fibroblast proliferation and fibroplasia that may contribute to implant loosening and failure.

Phospholipids as boundary lubricants in wear tests of prosthetic joint materials

The wear of ultra-high molecular weight polyethylene (UHMWPE) bearing surfaces in prosthetic joints is a significant clinical problem. Wear studies on prosthetic joints are therefore necessary in the improvement of their long-term performance. However, there is no practical and reliable lubricant available for the wear tests. The present study was the beginning of the development of “artificial joint fluid” for this purpose in the authors' laboratory. In prosthetic joints, effective boundary lubrication is known to take place. At the first stage, phospholipid–water dispersions were investigated. The phospholipids studied were dipalmitoylphosphatidylcholine (DPPC), which according to some studies functions as a boundary lubricant in the natural joints, and soybean lecithin, which contains some of the same phospholipids as joint fluid. The material combination used in the tests was UHMWPE against Co–Cr–Mo alloy. The tests were run with a pin-on-flat reciprocator, a uniaxial hip joint simulator, and a three-axis hip joint simulator. Phospholipids had a remarkable effect on the wear of UHMWPE. Surprising features in the wear of UHMWPE in regard to boundary lubrication and polyethylene transfer were observed. Some macroscopic polyethylene debris was produced, but the actual wear of the polyethylene component was still negligible, quite irrespective of whether the polyethylene transfer to the Co–Cr–Mo counterface was absent, mild or heavy. However, the fact that polyethylene transfer occurred in some tests and that the wear was negligible differs from typical clinical observations. More tests are needed and will be done to clarify the role of phospholipids as boundary lubricants in prosthetic joints.

Analysis of polyethylene wear debris using micro-Raman spectroscopy: a report on the presence of beta-carotene.

This paper describes micro-Raman spectroscopy of ultra-high molecular weight polyethylene wear debris isolated from revised knee replacements. The novel application of micro-Raman spectroscopy to the analysis of in vivo-generated wear debris was used to evaluate the chemical nature of individual, retrieved polyethylene particles. The analysis revealed the presence of beta-carotene on particles from both synovial fluid and tissue samples. Raman analysis of retrieved polyethylene tibial inserts also revealed localized beta-carotene signals within the primary wear region. In this paper, a mechanism is suggested that may account for the coupling of beta-carotene and polyethylene wear debris. We also discuss the origin of beta-carotene within the implanted joint and the implications that beta-carotene, an anti-oxidant, has for the overall host response to polyethylene orthopedic components.

Reduction in the initial wear of ultrahigh molecular weight polyethylene after compressive creep deformation

Although the wear of ultrahigh molecular weight polyethylene (UHMWPE) total joint implant components has received much attention, the creep of this polymer has been inadequately studied. The objectives of this study were to determine whether creep affects the wear of UHMWPE and, if so, to measure the magnitude of this effect. Cylindrical specimens were machined from GUR 4150HP extruded unirradiated UHMWPE rod stock, compressed at three different pressures (0, 4 and 8 MPa) for 10 000 min to simulate creep, and then unloaded for 10 000 min. Wear tests were conducted by unidirectionally sliding the ends of these UHMWPE cylinders at a speed of 125 mm s −1 on a highly polished stainless steel disc with a contact pressure of 4 MPa in bovine serum. Wear of the compressed specimens was only 38% as great as that of the noncompressed specimens ( p < 0.01). There was no significant difference in the amount of wear of specimens compressed at pressures of 4 MPa vs. 8 MPa. It is presently unclear whether this reduction in wear is due to a creep-induced reduction in asperity height, or to a creep-induced increase in UHMWPE's wear resistance.

The wear of ultra-high molecular weight polyethylene sliding on metallic and ceramic counterfaces representative of current femoral surfaces in joint replacement.

A number of studies have investigated the influence of surface roughness on the wear of ultra-high molecular weight polyethylene (UHMWPE) in total joint replacement. The results of these studies have shown that the wear factor is proportional to the counterface roughness raised to a power greater than one. In this laboratory study, the effect of surface finish of several biomaterials on the wear of UHMWPE was studied. The study was conducted using reciprocating pin-on-plate wear tests with bovine serum as a lubricant. The biomaterials investigated as the counterface material included stainless steel, cast cobalt chrome (CoCr), CoCr (ASTM F799), alumina ceramic and zirconia ceramic. The counterface topographies of the wear plates were produced using techniques representative of current manufacturing methods. The surface roughness of the wear plates was varied in the range Ra = 0.005-0.04 micron; this was representative of femoral heads and femoral knee components currently used clinically. Metals and ceramics with a similar surface roughness produced a similar wear rate of UHMWPE. For the limited range of smooth counterfaces used in this study only a moderate correlation was found between the surface roughness and the wear factors. For a change in counterface roughness Ra of 0.005 to 0.04 micron, the wear factor increased from 7.4 +/- 1.6 to 16.5 +/- 2.4 x 10(-9) mm3/N m (mean +/- standard error). This variation in counterface roughness had much less effect in wear than previously reported for rougher counterfaces. For an extended range of counterface roughness, a stronger correlation was found using an exponential function for the regression fit. The exponential function shows the benefits of decreased wear with decreased surface roughness. Although the wear rate decreased less rapidly with decreased counterface roughness for Ra values below 0.05 micron, there were significant advantages to be gained from improved femoral head roughness to below 0.01 micron Ra.

The influence of stress conditions on the wear of UHMWPE for total joint replacements.

In vitro studies of the effect of contact stress on the wear of ultra high molecular weight polyethylene (UHMWPE) in orthopaedic applications have produced contradictory results which predict both increased and decreased wear with increasing contact stress. In vivo studies of functioning hip prostheses have reported that 22 mm femoral heads generate lower linear and volumetric wear rates than 32 mm femoral heads. The effect of decreasing the head size will increase the contact stress but decrease the sliding distance per motion cycle. The present study consists of wear experiments under a range of contact stress magnitudes and application conditions in order to simulate the wear processes occurring in vivo. The results from these tests indicated that the wear factor actually decreases with increasing contact stress if the stress was not varied with time. If a time dependent or spatially varying stress was applied, the wear factor can increase greatly when compared to similar magnitude constant contact stress. This effect may be due to the complex relationship between the rate of wear particle generation and the rate at which the particles are released from the interface. The results of these wear experiments are discussed in terms of the influence of the stress conditions upon potential wear processes in total hip and knee prostheses.

Tribological behaviour of Ti6Al4V modified by surface treatments

At present, there are no good materials that can substitute ultra-high molecular weight polyethylene (UHMWPE), therefore the only way forward is to find a material for femoral heads with high wettability and hardness able to minimize the wear phenomena between metal and UHMWPE. In this work, the effects of surface treatments to improve the tribological behaviour of titanium alloy (Ti6Al4V) were studied. Ion implantation, CVD and PVD were the surface treatments investigated. Ti6Al4V modified and not modified samples were tested against γ-ray sterilized UHMWPE pins using a pin-on-flat wear test machine. The results have been compared with the wear behaviour of stainless steel (AISI 316L). Tests were carried out in accordance with ASTM F 732-82 practice, a specific wear test for materials used in total joint prostheses. Metal samples were characterized by SEM micrographs, roughness and hardness measurements, wettability and friction coefficient. UHMWPE wear rates were assessed by weighing the pins at intervals of 250 000 cycles and were expressed by linear regression analysis applied to the weight losses. Ion implantation of the titanium alloy results in lower wear of UHMWPE pins, in particular, chromium implantation is the most efficient among all surface treatments. A tentative explanation of the results is given.

Ultra-high molecular weight polyethylene wear debris generated in vivo and in laboratory tests; the influence of counterface roughness.

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.