The effects of high dose irradiation on the cross-linking of vitamin E-blended ultrahigh molecular weight polyethylene.
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.
Massachusetts General Hospital, Department of Orthopaedic Surgery, USA.
Ebru
E
Oral
Christine
C
Godleski Beckos
Arnaz S
AS
Malhi
Orhun K
OK
Muratoglu
D000975:Antioxidants / Q000737:chemistry / Q000528:radiation effects; D001672:Biocompatible Materials; D019544:Equipment Failure Analysis; D005720:Gamma Rays; D008422:Materials Testing; D011095:Polyethylenes / Q000737:chemistry / Q000528:radiation effects; D013314:Stress, Mechanical; D014810:Vitamin E / Q000737:chemistry / Q000528:radiation effects
D000975:Antioxidants; D001672:Biocompatible Materials; D011095:Polyethylenes; C111601:ultra-high molecular weight polyethylene; D014810:Vitamin E