An application of polyvinyl formal to total joint replacement

Abstract

Wear and material characteristics of polyvinyl formal (PVF) as an artificial articular cartilage have been investigated. The goal of that is to apply the PVF with low elastic modulus to bearing material for the next generation of total joint replacement. The PVF is made from polyvinyl alcohol (PVA), and this poromeric and hydrophilic polymer is expected to improve not only weeping lubrication but also boundary or mixed lubrication abilities in natural synovial fluid. A multi-sliding test, where a rotating stainless steel ball contacted a rotating PVF plate stationary, shows that all three of the PVFs provided for tests had high wear resistance. However, some PVFs were damaged by a reciprocating test, in which a stationary stainless steel ball was on a reciprocating PVF plate. Those results suggested that wear resistance of the PVF was less subject to the influence of multi-sliding motions, which was pointed out to the wear of an ultra-high molecular weight polyethylene as the same polymeric material. It must be noted that low elastic material such as PVF suffers from fatigue fracture. In reciprocating sliding, ploughing effect to PVF was thought to be real and substantive problem, so that the fatigue fracture would be observed. The PVF is one of promising artificial articular cartilage material, because it could apply to four-axis knee joint simulator (axial load, medial/lateral rotation, flexion/ extension, anterior/posterior) at the present stage, where a PVF tibial bearing and conventional femoral bearing were used respectively. The wear track of the PVF surface could not be observed until at least 1.0 million cycles. We expect that the durability performance of the PVF would be prolonged, if geometric designs of tibial and femoral components were refined to decrease contact pressure.