The effect of molecular orientation and acetylene-enhanced crosslinking onthe wear of UHMWPE in total artificial joints

This paper investigates the benefits of combining roll-drawing and acetylen e-enhanced crosslinking to alter the mechanical properties of the ultra hig h molecular weight polyethylene (UHMWPE) used in total hip and knee replace ments, with the aim of improving its resistance to wear. UHMWPE was process ed via crosslinking, roll-drawing and a combination of crosslinking and rol l-drawing and subjected to gel content analysis, tensile tests, X-ray diffr action and wear tests using different types of motion and smooth and rough counterfaces. Purely roll-drawn materials with length and width draw ratios of lambda (l) x lambda (w)= 1.3 x 1.0 and lambda (l) x lambda (w) = 1.6 x 0.9 respective ly, were found to have lower wear factors in a unidirectional motion test w ith a rough counterface when compared to the virgin material. The crosslinked roll-drawn material, with length and width draw ratios of l ambda (l) x lambda (w) = 1.6 x 0.9, was seen to possess five crosslinks per initial number average molecule. This crosslinked and roll-drawn material showed 5.5 times less wear than the virgin material in a multidirectional m otion test with a smooth counterface and 1.4 times more wear than the virgi n material in a unidirectional motion test with a rough counterface. Hence this study supports previous work by the authors that acetylene-enhan ced crosslinked materials may show benefits for a total hip replacement, bu t only where the femoral head remains smooth. The improvements in wear with the roll-drawn material in unidirectional tests were smaller, but may prov e to have some benefits in the knee. (C) 2001 Kluwer Academic Publishers.