Spatial geometric effects on the friction coefficients of UHMWPe

Multi-directional wear of ultra-high molecular weight polyethylene (UHMWPe) is of particular interest due to its wide-spread use as a bearing component polymer in orthopedic implants. To date, attempts to quantify wear mechanisms have depended greatly upon material orientation theories and average wear values over long periods in specific motions. This study introduces spatially resolved in situ friction coefficient measurements over relevant motion paths with a tribometer that provides uniform pressure and velocity under the pin. Normal and friction forces were measured simultaneously under dry and lubricated conditions during curvature-modulated paths. Spatially resolved friction coefficients increased with decreasing radius of curvature, which is consistent with the hypothesis that molecular chain alignment during unidirectional sliding is disrupted in multi-directional sliding.