Degradation Mechanism and Effects of Vitamin E addition in UHMWPE Hip Implants

University dissertation from Polymer Science & Engineering Center for Chemistry and Chemical Engineering Lund University

Abstract: Wear of the UHMWPE component is one of the major concerns in joint replacement surgery, triggering prosthetic loosening leading to revision. The understanding of the mechanisms of material degradation, especially in regard to oxidation, is one of the keys to significantly improve the mechanical properties. This work focused on the relationship between the failure mechanism, crosslinking and oxidation of the material. The effects of gamma-irradiation and annealing were investigated. ƒ×-Irradiation and aging cause oxidation of the material, and annealing at high temperature can significantly reduce this oxidation. Oxidation leads to a decrease in mechanical properties and wear resistance. This work also investigated the effect of the addition of an antioxidant, Vitamin E (VE) to the material. VE improves the oxidation resistance of irradiated UHMWPE but has also some impact on the mechanical properties, wear and oxidation of irradiated UHMWPE. Irradiation in presence of VE leads to an inhomogeneous material, a decrease in crosslink density and molecular weight. The morphology of the resulting material is consistent with a composite-like morphology where highly crosslinked domains are imbedded in a less crosslinked matrix. It was found that the mechanical properties of irradiated VE-containing materials depend on the VE concentration and appeared to be optimal for 0.2 w%VE. Volumetric wear is directly related to crosslink density. On the other hand, the coefficient of friction is related to the mechanical properties of the material, but not directly to the crosslink density.

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