Study of fatigue resistance of chemical and radiation crosslinked medical grade ultrahigh molecular weight polyethylene.

The aim of this work is to understand the role of chemical and radiation induced crosslinking on the fatigue crack propagation resistance of medical grade ultrahigh molecular weight polyethylene (UHMWPE). In recent years, the need to improve the tribological performance of UHMWPE used in total joint replacements has resulted in the widespread utilization of crosslinking as a method to improve wear resistance. Although crosslinking has been shown to drastically improve the wear resistance of the polymer, the potential trade-off in fatigue properties has yet to be addressed. Fatigue crack propagation resistance is a concern in tibial inserts where large cyclic stresses are sufficient to drive the growth of subsurface cracks that potentially contribute to delamination wear mechanisms. For clinical relevance, the combined effects of sterilization and aging are examined in two commercially available crosslinked resins. Nonsterile and unaged resins serve as a control. To evaluate the effect of crosslinking, a comparison is made to uncrosslinked resins. Scanning electron microscopy is used to provide an understanding of fatigue fracture mechanisms in the crosslinked polymers. The results of this study show that the current level of crosslinking used in orthopedic resins for enhanced wear resistance is not beneficial for fatigue crack propagation resistance.