In vitro wear performance of standard, crosslinked, and vitamin-E-blended UHMWPE

Crosslinked vitamin-E-stabilized polyethylene acetabular cups were compared with both commercially available conventional and custom-crosslinked polyethylene acetabular cups in terms of wear behavior, in a hip joint simulator for five millions cycles, using bovine calf serum as lubricant. We correlated the wear experiments results with the chemical characterization of the investigated materials: Fourier transformed infrared (FTIR) spectroscopic analyses, differential scanning calorimetry, and crosslink density measurements were used to assess the chemical characteristics of the pristine materials. In addition, further FTIR analyses and cyclohexane extraction were carried out after the simulator experiments. Lipids absorption was observed in all tested specimens and it has been shown to strongly affect the results of the wear test. Corrected gravimetric wear measurements showed that vitamin-E blended, crosslinked polyethylene wore more than the traditional crosslinked polyethylene but exhibited a much lower wear than conventional ultrahigh-molecular weight polyethylene. The chemical analyses showed that the addition of vitamin E reduced the crosslinking efficiency. Given the correlation between crosslink density and wear resistance, this gave an explanation for the observed wear performances.