Wear and friction of medical grade polyurethane sliding on smooth metal counterfaces

Abstract

There is considerable interest at the present time in the development of ‘cushion joints’ as alternative forms of total replacement joints for the body. Such joints promote the development of fluid film lubrication by using compliant bearing materials like polyurethane. The wear and friction of medical grade polyurethane sliding on smooth metal counterfaces have been studied in the work reported in this paper. It has been found that the geometry of the wear pins and the lubrication conditions have a significant effect upon the results obtained. For the wear pins with a small cone angle, both the coefficient of friction (less than 0.01) and the wear factor (less than 10 −8 mm 3 N −1 m −1) were very low as a result of fluid film lubrication. However, for the wear pins with a large cone angle, both the coefficient of friction (approximately 0.02) and the wear factor (approximately 10 −6 mm 3 N −1 m −1) were significantly increased as a result of a mixed lubrication regime. Under similar mixed lubrication conditions the wear of ultra high molecular weight polyethylene was some two orders of magnitude less than that of polyurethane. Furthermore, the results clearly demonstrated that only with fluid film lubrication and a greatly reduced coefficient of friction is the wear of the polyurethane superior to that of ultra high molecular weight polyethylene.