Can accelerated aqueous aging simulate in vivo oxidation of gamma-sterilized UHMWPE?

Oxidation of ultrahigh molecular weight polyethylene (UHMWPE) gamma-sterilized arthroplasty components occurs in vivo. Though accelerated in vitro protocols have been developed to test the relative oxidation resistance of various types of UHMWPE, it is desirable to develop an accelerated aging protocol that more closely approximates the in vivo environment. The goal of this study was to investigate the effects of temperature, solute, and oxygen partial pressure in aqueous media on the oxidation of gamma-sterilized UHMWPE, as the basis for the development of improved accelerated aging protocols. The accelerated oxidation behavior of gamma-sterilized GUR 1150 was studied at 60 and 70 degrees C in an open vessel filled with distilled water or PBS in equilibrium with a controlled partial pressure of oxygen. The extent of oxidation was assessed using standardized mechanical and chemical evaluation techniques (small punch and Fourier transform infrared spectroscopy). Accelerated oxidation of UHMWPE was achieved in aqueous environments; however, both clinically relevant and nonrelevant oxidation species (e.g., aldehydes) were observed for long aging times at 60 degrees C, and for all aging times at 70 degrees C. These findings point the way to the development of an accelerated aging protocol. The current data, considered in conjunction with real-time aging studies, suggest that a temperature between body temperature and 60 degrees C may accelerate oxidative degradation without altering the oxidative patterns encountered in vivo.