High Pressure Crystallization of Vitamin E‐containing Radiation Cross‐linked UHMWPE

Abstract

One of our aims in developing ultrahigh molecular weight polyethylene (UHMWPE) joint implants is to improve the fatigue strength of cross‐linked UHMWPEs without sacrificing their wear resistance induced by cross‐linking. High pressure crystallization (HPC) of uncross‐linked UHMWPE, which results in the formation of less hindered extended chain crystals, increased fatigue strength. Vitamin E, also an antioxidant, acted synergistically with HPC and the resulting UHMWPE had increased wear and fatigue strength. In this study, we hypothesized that vitamin E‐blended, cross‐linked, and high pressure crystallized UHMWPE (X‐VEHPE) would have higher wear resistance and fatigue strength compared to radiation cross‐linked UHMWPE. To test this hypothesis, we irradiated 0.1 wt% vitamin E‐blended UHMWPE, subsequently radiation cross‐linked it to various doses and terminally high pressure crystallized it. We used bi‐directional pin‐on‐disc wear testing, tensile mechanical testing, and fatigue crack propagation resistance testing. We found that X‐VEHPE required less radiation dose and less cross‐linking to achieve the same wear rate when compared to irradiated UHMWPE and had improved fatigue resistance at the same wear rate. Therefore, this UHMWPE presented about 46 and 87% improvement in fatigue strength compared to irradiated and irradiated/melted UHMWPE and may be a feasible alternative for joint implants.