Diffusion of vitamin E in ultra-high molecular weight polyethylene

Abstract

Vitamin E-doped, radiation cross-linked ultra-high molecular weight polyethylene (UHMWPE) is developed as an alternate oxidation and wear resistant bearing surface in joint arthroplasty. We analyzed the diffusion behavior of vitamin E through UHMWPE and predicted penetration depth following doping with vitamin E and subsequent homogenization in inert gas used to penetrate implant components with vitamin E. Cross-linked UHMWPE (65-and 100-kGy irradiation) had higher activation energy and lower diffusion coefficients than uncross-linked UHMWPE, but there were only slight differences in vitamin E profiles and penetration depth between the two doses. By using homogenization in inert gas below the melting point of the polymer following doping in pure vitamin E, the surface concentration of vitamin E was decreased and vitamin E stabilization was achieved throughout a desired thickness. We developed an analytical model based on Fickian theory that closely predicted vitamin E concentration as a function of depth following doping and homogenization.

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

“…The main goal of diffusing vitamin E into radiation-crosslinked UHMWPE is to obtain enough vitamin E throughout implants to protect against long-term oxidation. A two-step diffusion process at elevated temperatures below the melting point was developed involving doping of UHMWPE with vitamin E with subsequent homogenization [63]. Vitamin E improves the oxidative resistance of irradiated UHMWPE in vitro using either method although there are differences in concentration and radiation exposure.…”

“…The presence of vitamin E in UHMWPE during irradiation protects the polymer from oxidation but reduces the efficiency of crosslinking [56,57,65] while the vitamin E itself is reacted; therefore, the vitamin E concentration and the subsequent radiation dose must be optimized to obtain a simultaneously wear-and oxidation-resistant UHMWPE. The alternative method is the diffusion of vitamin E into UHMWPE after radiation crosslinking [62,63]. The crosslinking efficiency of UHMWPE is not adversely affected in this method since vitamin E is not present during irradiation.…”

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

“…The first method is diffusing vitamin E into UHMWPE after radiation crosslinking [44,45]. This method incorporates vitamin E into UHMWPE using a two-step process.…”

“…This method incorporates vitamin E into UHMWPE using a two-step process. The first step is post-radiation doping with vitamin E, and the second step is a further homogenization into inert atmosphere [44,45]. The homogenization step is necessary since it can achieve an adequate antioxidant concentration throughout the implants.…”

Comparison of stabilization by Vitamin E and 2,6-di-tert-butylphenols during polyethylene radio-thermal-oxidation

“…Some antioxidant profiles were reported in the case of UHMWPE displaying a vitamin E concentration gradient before irradiation. After irradiation, vitamin E residual concentration actually displays a maximum in the subsurface layers (Oral et al, 2007). This is an encouraging argument in favor of the model even if a most complete set of simulations is needed together with more accurate data on crystallinity profile, vitamin E and oxygen diffusivity etc... -D AH = 9.2×10 -10 cm 2 s -1 for AO1 from Roe et al (1974), Moisan (1980), Limm and Hollifield (1996) -D AH = 2.3×10 -8 cm 2 s -1 for AO2 from Moisan (1980).…”