Surface cross‐linked UHMWPE using peroxides

Abstract

Crosslinking of ultra-high molecular weight polyethylene (UHMWPE) has been successfully used to improve its wear performance. Wear is a surface phenomenon and limiting crosslinking to a layer only on the surface is desirable, as crosslinking of the bulk of the implant reduces its mechanical strength and toughness. We present a novel technique to surface crosslink consolidated UHMWPE/vitamin-E blends by diffusing an organic peroxide into the polymer at moderate temperatures, followed by heating to above the peroxide decomposition temperature to cause crosslinking on the surface. We characterized the surface crosslink density and wear rate of surface crosslinked UHMWPE/vitamin-E blends with two different types of peroxides. Both peroxides resulted in surface crosslinking with an increase in wear resistance comparable to the state-of-the-art highly crosslinked UHMWPE used for orthopedic implants. The addition of the antioxidant vitamin-E led to higher oxidation resistance. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:2551-2556, 2017.

Research into the thermal stability and mechanical properties of vitamin E diffusion modified irradiation cross-linked graphene oxide/ultra-high molecular weight polyethylene composites

“…Osteolysis, as a clinical problem, has been the driving force behind the development of UHMWPE. 1,2 During the last 20 years, cross-linking [3][4][5][6] and lling with graphene oxide (GO) [7][8][9][10][11] have been widely used to enhance the performance of UHMWPE. Cross-linked materials and materials with added GO have shown remarkable increases in longterm overall survival in total joint replacements around the world, due to signicantly improved mechanical properties.…”

Surface cross‐linked ultra high molecular weight polyethylene by emulsified diffusion of dicumyl peroxide

“…One constraint was the maximum concentration of the peroxide in the emulsion. Although pure peroxide can be used to cross‐link the surface of 0.1 wt % vitamin E‐blended UHMWPE using the doping/decomposition method, it was not known if a lower concentration of peroxide could also achieve the desired extent of surface cross‐linking. Thus, we emulsified DCP with Tween 20, a common emulsifier used in drug formulations, to test this hypothesis.…”

“…Using a peroxide with a decomposition temperature close to the molding temperature of UHMWPE (typically 170–210°C) prevents premature cross‐linking of the resin before consolidation. In the second method, peroxide can diffusion into an already consolidated UHMWPE sample at below the peroxide decomposition temperature followed by heating above that temperature allows cross‐linking if the sample in regions where peroxide is able to penetrate . The main benefit of the latter method is to limit cross‐linking to the surface of the polymer intended for use as a bearing surface, resulting in increased wear resistance on the surface with improved toughness in the bulk compared with a uniformly cross‐linked UHMWPE …”

“…We previously showed that diffusing dicumyl peroxide (DCP) followed by its decomposition leads to surface cross‐linking of vitamin E‐blended UHMWPE with wear resistance comparable to commercially available radiation cross‐linked UHMWPE implants . The melting point of DCP is 39°C and its 1‐h decomposition temperature is 137°C.…”

Polyethylene in total knee arthroplasty: Where are we now?

“…1,2,21,22 More recent attempts have been made to spatially limit cross-linking to the surface of the implant, maximizing overall toughness while decreasing surface wear rates. 23,24…”