Effect of temperature on UHMWPE and VEXLPE friction and wear against CoCr in noncyclic tests

Abstract

In prosthetic joints, frictional heating may cause protein denaturation in synovial fluid which may affect its lubrication properties. In arthroplasty, conventional ultra-high molecular weight polyethylene (UHMWPE) is being gradually replaced by vitamin E stabilized, extensively cross-linked UHMWPE (VEXLPE) with a superior combination of wear and oxidation resistance. There is scarcity of literature on UHMWPE vs.VEXLPE friction. A noncyclic, single-station friction measurement device, the Friction RandomPOD, was recently introduced. The direction of sliding, velocity, acceleration, and load varied randomly within certain, biomechanically justified limits. The measurement of the coefficient of friction was based on a three-axial load cell. In order to increase the testing capacity, the number of test stations was now increased to 4 using similar load cells. One-week tests were performed with pins made of UHMWPE and VEXLPE against CoCr in calf serum lubrication at 4 °C, 20 °C and 37 °C. The lower temperatures were included to prevent or retard protein denaturation. The lowest friction and wear were observed at 37 °C. At this temperature, the mean of the coefficient of friction of VEXLPE was 55% lower than that of UHMWPE. The wear of VEXLPE was always lower than that of UHMWPE.