Long Term Effects of Annealing Temperature, Storage Condition, and Antioxidants on Oxidative Behavior of Free Radicals in Medical Grade UHMWPE*

Ultra-High Molecular Weight Polyethylene (UHMWPE) is used as a medical joint replacement material. Since 1962, materials improvements have been made and the lifetimes of the components have increased significantly. However, challenges remain, one being the focus of this study: free radicals in the UHMWPE, created mostly during necessary radiation treatments (e.g., sterilization), which induce oxidative degradation when exposed to oxygen. Heat treatments (annealing) and antioxidants (e.g., vitamin E) attempt to minimize oxidation, through reduction of the root cause: the free radicals which enable oxidation in the first place. Related annealing research for biocompatible UHWMPE was started over 20 years ago, including at the University of Memphis Physics Department, as a part of a project initiated in 1998 between the State University of New York at Buffalo (SUNY Buffalo) and the University of Memphis under the sponsorship of the NSF Center for Industry/University Collaborative Research on Biosurfaces. The samples have been aging over 20 years, and antioxidant-containing samples for over 10 years. The present study was aimed to report the change in free radical concentration with temperature, storage condition, and antioxidants. Results do show a change with storage temperature, greater in one type vs. another, and strong oxidation prevention in all inert-stored samples, and that vitamin E plays an important role in quenching the free radicals after irradiation.