Development of artificial articular cartilage

Attempts have been made to develop an artificial articular cartilage on the basis of a new viewpoint of joint biomechanics in which the lubrication an d load-bearing mechanisms of natural and artificial joints are compared. Po lyvinyl alcohol hydrogel (PVA-H), 'a rubber-like gel', was investigated as an artificial articular cartilage and the mechanical properties of this gel were improved through a new synthetic process. In this article the biocompatibility and various mechanical properties of t he new improved PVA-H is reported from the perspective of its usefulness as an artifical articular cartilage. As regards lubrication, the changes in t hickness and fluid pressure of the gap formed between a glass plate and the specimen under loading were measured and it was found that PVA-H had a thi cker fluid film under higher pressures than polyethylene (PE) did. The mome ntary stress transmitted through the specimen revealed that PVA-H had a low er peak stress and a longer duration of sustained stress than PE, suggestin g a better damping effect. The wear factor of PVA-H was approximately five times that of PE. Histological studies of the articular cartilage and synov ial membranes around PVA-H implanted for 8-52 weeks showed neither inflamma tion nor degenerative changes. The artificial articular cartilage made from PVA-H could be attached to the underlying bone using a composite osteochon dral device made from titanium fibre mesh. In the second phase of this work, the damage to the tibial articular surfac e after replacement of the femoral surface in dogs was studied. Pairs of im plants made of alumina, titanium or PVA-H on titanium fibre mesh were inser ted into the femoral condyles. The two hard materials caused marked patholo gical changes in the articular cartilage and menisci, but the hydrogel comp osite replacement caused minimal damage. The composite osteochondral device became rapidly attached to host bone by ingrowth into the supporting mesh. The clinical implications of the possible use of this material in articular resurfacing and joint replacement are discussed.