Vitamin E can be used to hinder scissioning in radiation cross‐linked UHMWPE during high‐temperature melting

Abstract

High-temperature melting (HTM) of ultrahigh molecular weight polyethylene (UHMWPE) was shown to improve its elongation and toughness. This was believed to be due to increased scissioning and increased diffusion of polymer chains. It was hypothesized here that the toughness of previously radiation cross-linked UHMWPEs could also be improved by HTM. To test this hypothesis, the wear resistance, tensile mechanical properties, and Izod impact strength of radiation cross-linked virgin (no additive) and antioxidant-blended (with vitamin E) UHMWPEs were tested. The results suggested that although the impact strength of crosslinked UHMWPEs could be improved significantly by HTM, the wear resistance was decreased. Thus, this procedure can be optimized to be especially suited in high-stress applications, such as total knee replacements with lessened wear concerns. V C 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42735.

Chemically Cross‐Linked UHMWPE With Superior Toughness

“…When radiation cross‐linked UHMWPE was HTM, it was shown that increasing exposure time and temperature increased the terminal VI, which is an indication of increased chain scissioning . An optimum window of operating temperature and HTM duration was observed, where toughness could be improved without sacrificing wear resistance to chain scissioning.…”

Oxidation resistance and abrasive wear resistance of vitamin E stabilized radiation crosslinked ultra‐high molecular weight polyethylene

“…It suggests that if a large Vitamin E content is desired to combat oxidation due to free radicals associated with other external sources such as cyclic loads 38 or infiltration of the implant with oxidizing species, 39 then the UHMWPE must be subjected to higher radiation doses in order to counter the effects of reduced crosslink density and wear resistance. A larger radiation dose would however imply a larger reservoir of free radicals in the lamellar regions of HXLPEs, thereby requiring more Vitamin E. Therefore, alternate crosslinking processes 25 or alternate antioxidants, which do not suppress crosslinking to such a large extent, 40 may be preferred to conventional irradiation of HXLPEs at room temperatures containing Vitamin E. It must be recognized that the type of wear investigated in this study was primarily the generation of particulate wear and did not investigate other modes of wear such as those related to fatigue processes like delamination wear. Such wear modes would require more knee-like articulation, so the results of this study can only be interpreted in terms of slowing the rate of generation of wear particles of UHMWPE under hip-like articulation involving a multidirectional wear pattern.…”

“…7,8 It also accelerates the generation of particulate wear in joint components. [21][22][23][24][25][26][27][28] Vitamin E can either be blended into the UHMWPE resin prior to molding 29 or diffused into the implant after radiation. This initial increase in crosslinking indicated that it increases resistance of UHMWPE to wear and leads to the development of highly crosslinked UHMWPEs (HXLPEs), which were subjected to higher radiation doses of gamma or electron beam radiation (50-100 kGy dose range), not as a final sterilization step of the packaged implant but as a processing step for molded sheets and rods of UHMWPE, prior to the fabrication of the implant.…”

“…[18][19][20] While irradiation has been unavoidable due to its large increase in wear resistance, post-radiation treatments to reduce free radical content in irradiated HXLPEs can be avoided by incorporation of a stabilizer, such as Vitamin E or other biocompatible antioxidants. [21][22][23][24][25][26][27][28] Vitamin E can either be blended into the UHMWPE resin prior to molding 29 or diffused into the implant after radiation. 30 The advantage of the latter over the former process is that it was shown that Vitamin E can decrease the formation of crosslinks in the amorphous regions by scavenging free radicals before crosslinking can occur.…”

High temperature homogenization improves impact toughness of vitamin E-diffused, irradiated UHMWPE

“…It was recently shown that high temperature melting (HTM) of radiation cross‐linked UHMWPE at above 280°C can improve its toughness, presumably due to combined effects of controlled chain scissioning and increased inter‐granular diffusion . We hypothesized that homogenization of vitamin E‐doped, radiation cross‐linked UHMWPE at above 280°C could increase its toughness.…”