The effects of high dose irradiation on the cross-linking of vitamin E-blended ultrahigh molecular weight polyethylene

Biomaterials. 2008 Sep;29(26):3557-60. doi: 10.1016/j.biomaterials.2008.05.004. Epub 2008 Jun 2.

Abstract

Vitamin E-stabilized, highly cross-linked ultrahigh molecular weight polyethylene (UHMWPE) is a promising oxidation and wear resistant UHMWPE with improved mechanical strength in comparison with the first generation, irradiated and melted UHMWPE. One approach of incorporating vitamin E in UHMWPE is through blending of vitamin E in UHMWPE powder followed by consolidation and radiation cross-linking. However, radiation cross-linking efficiency of UHMWPE decreases in the presence of vitamin E. Therefore an optimum vitamin E concentration and radiation dose level need to be determined to achieve a cross-link density comparable to 100-kGy irradiated and melted UHMWPE, which has shown excellent wear properties in vivo. We investigated the cross-link density and mechanical properties of vitamin E-blended UHMWPEs as a function of vitamin E concentration in the blend and gamma irradiation doses up to 200kGy. We found that 0.3wt% vitamin E-blended UHMWPE could not be cross-linked above a cross-link density achieved at a radiation dose of 65kGy for virgin UHMWPE and 1.0wt% vitamin E-blended UHMWPE could not be cross-linked above a cross-link density achieved at a radiation dose of 25kGy for virgin UHMWPE even when the these UHMWPEs were irradiated to a radiation dose of 200kGy. In addition, higher plasticity at vitamin E concentrations at and above 0.3wt% indicated that increased chain scissioning may be prevalent. Since the wear resistance of this irradiated UHMWPE would be expected to be low, vitamin E concentrations equal to or above 0.3wt% are not recommended for subsequent irradiation to achieve a wear resistant cross-linked UHMWPE. The long-term oxidative stability of irradiated blends with low vitamin E concentrations has yet to be studied to determine an optimum between cross-link density and long-term oxidative stability.

Publication types

  • Evaluation Study
  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antioxidants / chemistry
  • Antioxidants / radiation effects
  • Biocompatible Materials
  • Equipment Failure Analysis
  • Gamma Rays
  • Materials Testing
  • Polyethylenes* / chemistry
  • Polyethylenes* / radiation effects
  • Stress, Mechanical
  • Vitamin E* / chemistry
  • Vitamin E* / radiation effects

Substances

  • Antioxidants
  • Biocompatible Materials
  • Polyethylenes
  • ultra-high molecular weight polyethylene
  • Vitamin E