Trace concentrations of vitamin E protect radiation crosslinked UHMWPE from oxidative degradation

Abstract

The effect of very low concentrations of Vitamin E on the stability and mechanical behavior of UHMWPE remains unknown. We tested the hypothesis that the oxidation resistance of Vitamin E-blended UHMWPE would be influenced by trace doses of antioxidant, resin, and radiation treatment. Trace concentrations (< or =500 ppm w/w%) of alpha-tocopherol (Vitamin E) were blended separately with GUR 1020 and 1050 resins and molded into disks. From each disk, three groups of 10 mm thick blocks were machined: (1) no irradiation (control); (2) 30 kGy of gamma irradiation in nitrogen; and (3) 75 kGy of gamma irradiation in air. Specimens were subjected to three aging protocols: (a) no aging (control); (b) two weeks and (c) four weeks of accelerated aging in accordance with ASTM F 2003 (i.e., 70 degrees C and 5 atm oxygen). The minimum concentration of Vitamin E needed to stabilize UHMWPE during our accelerated tests depended upon the method of radiation processing. For the 30 and 75 kGy irradiated materials, the addition of 125 ppm or more Vitamin E was sufficient to maintain baseline mechanical and chemical properties through two weeks of accelerated aging. For these groups, the addition of 375 ppm or 500 ppm, respectively, was necessary to maintain baseline mechanical and chemical properties throughout the four-week accelerated aging period. UHMWPE resin molecular weight did not have an effect on oxidation behavior. The results of this experiment therefore supported our hypotheses that trace concentrations of Vitamin E, coupled with radiation treatment-but not resin grade-influence the mechanical and oxidative degradation behavior of UHMWPE.

Vitamin E-stabilized UHMWPE for Total Joint Implants: A Review

“…The oxidation cascade in irradiated polyethylene is therefore hindered, even in the presence of a small amount of vitamin E (0.05% wt%) [42,44].…”

“…The rationale for using vitamin E was twofold: improving oxidation resistance of irradiated UHMWPEs and improving the fatigue strength of irradiated UHMWPEs using an alternative to postirradiation melting [9,11,42,44,55,62,82].…”

Wear Performance of UHMWPE and Reinforced UHMWPE Composites in Arthroplasty Applications: A Review

“…The second method is blending a liquid antioxidant into the UHMWPE resin powder before the mixture consolidates into a near-implant form and radiation crosslinking is performed [39,[50][51][52]. This method is easier and takes shorter time to obtain uniform vitamin E concentration throughout the implant compared with the first method [53].…”

“…However, for the 0.8 wt% vitamin E stabilised material, the elastic modulus and tensile strength were 20% lower than that of the virgin and gamma sterilized UHMWPE, while the elongation and impact strength remained at the baseline values [58]. To sum up, the previous studies [51,52,58] showed that vitamin E alone with up to 0.4 wt% concentration have a marginal effect on the mechanical properties of UHMWPE. However, some studies [44,57,59] suggested that vitamin E-stabilised UHMWPE has a significantly higher tensile strength, yield strength, elongation at break and fatigue resistance, especially at concentrations exceeding 0.1 wt% [59].…”

“…The mechanical properties of vitamin E-stabilised UHMWPE are insensitive to the introduction of vitamin E up to the concentration of 0.4 wt% [51,52]. When vitamin E concentration is in a range of 0.01-0.05 wt%, vitamin E has a negligible effect on the mechanical properties of unsterilized and gamma sterilized UHMWPE [51]. Furthermore, for vitamin E concentration of 0 wt%, 0.1 wt%, 0.2 wt% and 0.4 wt%, the elastic modulus, elongation, tensile, and impact strength have no significant difference for both virgin and gamma sterilized UHMWPE [58].…”