Factors Affecting Traction Coefficients During Intermittent Sliding Motion in Textured Metal-Polyethylene Bearings
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In cases of severe arthritis, a metal-on-ultra-high molecular weight polyethylene (UHMWPE) total joint arthroplasty (TJA) is the primary solution. Wear of UHMWPE is a concern as it causes poor bearing performance and a decrease in the device’s lifespan. In this study, UHMWPE surface texturing has been proposed as a way to improve tribological conditions. Surface texturing has been studied previously under steady-state conditions, which is not representative of the harsh kinematic conditions occurring in daily living activities. Therefore, the objective of this study is to investigate the hypothesis that the proposed novel texturing approach improves tribological conditions during intermittent stop-dwell-start (SDS) motion by measuring the traction coefficient during the SDS phases. A custom waveform in a pin-on-disc friction and wear tester was created to simulate SDS loading conditions. Untextured and textured UHMWPE specimens were tested under three lubricating conditions (unlubricated, water and glycerin). Then, a method was developed to extract meaningful traction coefficient data from the SDS test results. Lastly, factors affecting the tribological conditions in the metal-UHMWPE system were investigated based on traction coefficient and wear analysis observations. The factors affecting the traction coefficient and wear were the introduction of texturing and the viscosity of the lubricant. The presence of a lubricant dominated when attempting to reduce the traction coefficient and wear. A significant reduction in traction coefficient was observed with both water and glycerin compared to unlubricated conditions in all phases of SDS motion, regardless of the surface geometry. Also, the higher the lubricant’s viscosity, the lower the traction coefficient and amount of wear. The introduction of the textured surface resulted in a significant reduction or no change in traction coefficient in the stop and start phases in the unlubricated and glycerin conditions. Also, no additional wear was observed when the surface was textured compared to untextured. Therefore, when the bearing system is properly lubricated, texturing is a promising approach to reduce traction and wear. It is therefore proposed that textured UHMWPE be further investigated as a solution to extend the lifespan on TJA.