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

Abstract

Chemical cross-linking of ultrahigh molecular weight polyethylene (UHMWPE) using an organic peroxide followed by high temperature melting results in a large increase in toughness accompanied by a decrease in cross-link density, which, surprisingly does not compromise the wear resistance. We compared the mechanical properties and wear behavior of a vitamin E blended, chemically cross-linked and high temperature melted UHMWPE produced by ram extrusion (PRX HTM) to those measured with the clinically available 100-kGy irradiated and melted UHMWPE (CISM 100). We also assessed the local biocompatibility of PRX-HTM in rabbit subcutaneous pouch and osteochondral defect models. The ultimate tensile strength and pin-on-disc wear rate were similar to CISM 100; whereas the elongation-at-break and impact toughness were much higher with PRX-HTM. The stress intensity factor range at crack inception was also higher with PRX-HTM. Accelerated aging did not result in any measurable oxidation or changes in mechanical properties. Hip simulator wear rate of acetabular liners made with PRX-HTM was 0.3 AE 0.4 mg/million-cycle, similar to that reported for CISM 100 liners. The wear particles were largely spherical with a number-averaged particle size of 0.95 μm with~75% of particles below 1 μm. The subcutaneous and osteochondral rabbit implantations showed no histological differences between PRX-HTM and the control CISM 100. Preclinical wear, mechanical, and biocompatibility testing of PRX HTM showed feasibility for the use of this material as a total joint arthroplasty implant bearing surface. This process has the potential of eliminating the additional step of radiation cross-linking by combining consolidation and cross-linking while improving toughness.

Chemically Cross‐Linked UHMWPE With Superior Toughness

“…Further testing including biocompatibility analysis is warranted for this material to be considered for clinical use. We have published further device testing for an optimized, large scale processed formulation of cross‐linked UHMWPE prepared by this process including FTIR analysis of residuals as well as biocompatibility of peroxide cross‐linked UHMWPE with high amounts of peroxide (with and without HTM) elsewhere . It was first found that HTM was very effective in removing any volatile and extractable compounds associated with peroxide decomposition.…”

Ultrahigh molecular weight polyethylene with improved crosslink density, oxidation stability, and microbial inhibition by chemical crosslinking and tea polyphenols for total joint replacements

“…The main advantage of chemical crosslinking over radiation crosslinking is that the crosslink density can be readily optimized by control over the peroxide content 19,23 . The crosslinking network is achieved uniformly throughout the material since the crosslinking is implemented in the melt state of the polymer 26 . It is suitable to fabricate the bearings with large thickness.…”

Quantitative Measurements of Backside Wear in Acetabular Hip Joint Replacement: Conventional Polyethylene Versus Cross-Linked Polyethylene

“…The particle analysis of the reported articular wear showed comparable results regarding the morphology [10,12,18]. Illgen et al described predominantly round particles from CPE (amount: 78%) and from XLPE (amount: 87%) [10].…”