Enhanced wear resistance of orthopaedic bearing due to the cross‐linking of poly(MPC) graft chains induced by gamma‐ray irradiation

We assumed that the extra energy supplied by gamma‐ray irradiation produced cross‐links in 2‐methacryloyloxyethyl phosphorylcholine (MPC) polymer grafted cross‐linked polyethylene (CLPE‐ g ‐MPC) and investigated its effects on the tribological properties of CLPE‐ g ‐MPC. In this study, we found that the gamma‐ray irradiation produced cross‐links in three kinds of regions of CLPE‐ g ‐MPC: poly(MPC) layer, CLPE‐MPC interface, and CLPE substrate. The dynamic coefficient of friction of CLPE‐ g ‐MPC slightly increased with increasing irradiation doses. After the simulator test, both the nonsterilized and gamma‐ray sterilized CLPE‐ g ‐MPC cups exhibited lower wear than the untreated CLPE ones. In particular, the gamma‐ray sterilized CLPE‐ g ‐MPC cups showed extremely low and stable wear. As for the nonsterilized CLPE‐ g ‐MPC cups, the weight change varied with each cup. When the CLPE surface is modified by poly(MPC) grafting, the MPC graft polymer leads to a significant reduction in the sliding friction between the surfaces that are grafted because water thin films formed can behave as extremely efficient lubricants. Such a cross‐link of poly(MPC) slightly increases the friction of CLPE by gamma‐ray irradiation but provides a stable wear resistant layer on the friction surface. The cross‐links formed by gamma‐ray irradiation would give further longevity to the CLPE‐ g ‐MPC cups. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 2008