Effects of surface texturing on the performance of biocompatible UHMWPE as a bearing material during in vitro lubricated sliding/rolling motion

The effect of surface texturing on the performance of biocompatible ultra-high molecular weight polyethylene (UHMWPE) as a bearing material has been investigated using the kinematic range of motions reported for a knee-joint replacement. An experimental apparatus consisting of a ball and a disk rotating independently from each other was used to compare the performance of UHMWPE textured versus plain surfaces, under different combinations of sliding and rolling motion, better known as sliding-to-rolling ratio (SRR). Performance was evaluated through the coefficient of traction of a tribosystem comprising a steel ball on a flat UHMWPE disk and distilled water at 36 °C, acting as lubricant. A square array of cavities with diameter D=0.397 mm and center-to-center spacing of 1.5 D was machined on UHMWPE disks. The experimental design considered two levels for cavity depth, D and D/2, and two for the applied load, 17 and 25 N. The SRR was varied from 1 to 11% and the mean speed range was set from 5 to 55 mm/s, covering the kinematics and contact pressure conditions of a sauntering cycle on a knee-joint replacement. Stribeck curves of the plain and textured surfaces were obtained and compared against one another. The results demonstrate that the proposed surface pattern reduces the coefficient of traction of the tribological system for the 17 N load in the entire kinematic range explored, while for the 25 N load the effects were more noticeable at low mean speed and SRR, corresponding to the beginning of motion.