Peroxide cross‐linked UHMWPE blended with vitamin E

Abstract

Radiation crosslinked ultrahigh molecular weight polyethylene (UHMWPE) is the bearing surface material most commonly used in total joint arthroplasty because of its excellent wear resistance. Crosslinking agents such as peroxides can also effectively increase wear resistance but peroxide crosslinked UHMWPE has low oxidative stability. We hypothesized that the addition of an antioxidant to peroxide crosslinked UHMWPE could improve its oxidation resistance and result in mechanical, tribological, and oxidative properties equivalent to currently utilized radiation crosslinked UHMWPEs. Various vitamin E (0.1-1.0 wt % and peroxide concentration (0.5-1.5 wt %) combinations were studied to investigate changes in crosslink density, wear rate, mechanical properties, and oxidative stability in comparison to radiation crosslinked UHMWPE. Peroxide crosslinking was more efficient as compared to radiation crosslinking in the presence of vitamin E with the former resulting in lower wear rate with vitamin E concentrations above 0.3 wt %. The tensile mechanical properties were comparable to and the impact strength was higher than those of the clinically relevant radiation crosslinked controls. We also determined that gamma sterilization of peroxide crosslinked vitamin E blends improved wear resistance further. In summary, peroxide crosslinking of vitamin E-blended UHMWPE may provide a feasible and economical alternative to radiation for achieving clinically relevant properties for total joint implants using UHMWPE. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 1379-1389, 2017.

Surface cross‐linked UHMWPE using peroxides

“…This is presumably due to increased penetration depth of peroxide with increased temperature during doping. In further analysis, the mechanical testing of surface cross‐linked UHMWPE using diffusion of emulsified peroxides similar to what was shown here corroborated improved toughness compared to uniformly cross‐linked UHMWPEs …”

“…Recently, techniques have been developed to improve the oxidation resistance of cross‐linked UHMWPEs by the incorporation of antioxidants, especially blending with the natural antioxidant vitamin E . The blending of vitamin E in peroxide cross‐linked UHMWPE was shown to improve the oxidation resistance of peroxide cross‐linked UHMWPE . In addition, higher concentrations of vitamin E could be used when using peroxide cross‐linking than when using radiation cross‐linking because peroxide cross‐linking was less sensitive to vitamin E as a free radical scavenger.…”

Chemically Cross‐Linked UHMWPE With Superior Toughness

“…The hindrance of cross‐linking in UHMWPE by the antioxidant vitamin E and the changes in related properties have been well documented in vitamin E‐blended, consolidated and radiation cross‐linked UHMWPE . It was also suggested that peroxide cross‐linking of UHMWPE may be less sensitive to the presence of vitamin E, thus enabling the use of higher concentrations of vitamin E in the blended UHMWPE. The target cross‐link density of approximately 260 mol/m 3 , which was the measured cross‐link density of 100‐kGy irradiated and melted highly cross‐linked control UHMWPE without any additives, was reached at 0.57 wt% peroxide for a 0.2 wt% vitamin E blend and at 0.79 wt% peroxide for a 0.5 wt% blend (intrapolated form the data presented in Fig.…”

An antioxidant stabilized, chemically cross‐linked UHMWPE with superior toughness

“…The incorporation of vitamin E also enabled peroxide cross‐linking of UHMWPE preventing oxidation during consolidation and cross‐linking. The addition of vitamin‐E also imparted excellent oxidative stability in finished articles . We recently introduced high temperature melting as a method to improve the fatigue toughness of cross‐linked UHMWPEs and advanced the application of this method to peroxide crosslinking of UHMWPE/vitamin‐E blends.…”

“…Chemical cross‐linking of UHMWPE blended with the organic peroxide 2,5‐Di ( tert ‐butylperoxy)‐2,5‐dimethyl‐3‐hexyne (P130) is optimal above 180°C, at which temperature the half‐life of P130 dissociation is around 1 min. This is possibly a reason why P130 cross‐linking of UHMWPE is less sensitive to the presence of vitamin E, enabling incorporation of a higher concentration of the antioxidant than that used with radiation cross‐linking . For example, while a 1 wt % vitamin E blended UHMWPE has a cross‐link density equivalent to conventional gamma sterilized UHMWPE when irradiated to 200 kGy, it can have a cross‐link density equivalent to that of a highly cross‐linked UHMWPE when cross‐linked using 1 wt % peroxide.…”