The combined effects of crosslinking and high crystallinity on the microstructural and mechanical properties of ultra high molecular weight polyethylene

Ultra high molecular weight polyethylene (PE) has been used for more than forty years as the bearing surface in total joint replacements. In recent years, there have been numerous advances in processing conditions that have improved the wear resistance of this material. In particular, crosslinking has been shown to dramatically improve the wear behavior of this orthopedic polymer in simulator studies. This benefit to wear resistance, however, is accompanied by a decrease in mechanical properties such as ultimate tensile strength, ductility, toughness and fatigue resistance. This degradation to mechanical properties may have serious implications for devices with high stress concentrations or large cyclic contact stresses. Tailoring microstructure for improved structural performance is essential for implant design. In this work we examined the role of crystallinity and crosslinking on the microstructure and mechanical properties of PE. Crystallinity was increased with a high pressure process and crosslinking was obtained with gamma irradiation. Crystallinity was beneficial to fatigue crack propagation resistance and when coupled with crosslinking a polymer with both wear and fatigue resistance was obtained.