Effect of Gamma-Radiation Induced Oxidation and Crosslinking on the Wear Performance of Ultra-High Molecular Weight Polyethylene (UHMWPE) Acetabular Cups

摘要

The effect of gamma-radiation sterilization on the mechanical and physical properties of ultra-high molecular weight polyethylene (UHMWPE) has been studied in depth, but the effect on tribological properties remains a matter of considerable debate and contention. Most of the conclusions about the tribological properties are either hypothetical or based on wear testing that does not simulate the in vivo wear conditions adequately. In this paper, extensive hip simulator data are presented regarding the wear behavior of UHMWPE acetabular cups. The following sterilization treatments are considered: no sterilization, gamma-radiation in air, gamma-radiation in an inert atmosphere and stabilization, and ethylene oxide (EtO) sterilization. Hip simulator testing was conducted in both the anatomical and the inverted anatomical configurations. In the anatomical configuration, the stabilized UHMWPE acetabular cups demonstrated a reduction in wear of about 65percent over EtO sterilized acetabular cups and 20percent over air-irradiated cups. The unirradiated UHMWPE cups demonstrated the same wear behavior as EtO sterilized cups. In the inverted anatomical configuration, stabilized cups showed a 54percent reduction in wear over the EtO sterilized cups. Oxidation studies further showed that air-irradiated UHMWPE had a propensity for increased oxidation levels over time with a peak in the subsurface while stabilized acetabular cups showed consistetly lower oxidation levels with accelerated aging. Gel content analysis showed an increase in the insoluble constituents with gamma radiation, indicating an increase in crosslinks. Based on this study, it was concluded that gamma sterilization in an inert environment followed by thermal activation to accelerate free radical decay improves the tribological properties of UHMWPE while controlling any increase in oxidation levels even after accelerated aging.