Superior lubrication mechanism in poly(vinyl alcohol) hybrid gel as artificial cartilage

Abstract

With recent progress of material technologies, the wear resistance of ultra-high molecular weight polyethylene for total joint prostheses has been improved, but under severe conditions friction and wear problems have not yet been completely solved. Therefore, the application of artificial hydrogel cartilage with similar properties to natural articular cartilage is expected to solve the friction and wear problems by improvement of lubrication mechanism with superior tribological functions. In this study, reciprocating tests of four kinds of poly(vinyl alcohol) hydrogels were carried out and the biphasic finite element analysis was conducted. As artificial cartilage specimens, four kinds of poly(vinyl alcohol) hydrogels were prepared using the repeated freeze–thawing (FT) method, the cast-drying (CD) method and the hybrid method with different layered structure as FT on CD or CD on FT. In reciprocating test of ellipsoidal poly(vinyl alcohol) hydrogel specimen against flat glass plate in saline solution, four kinds of hydrogels exhibited very different frictional levels as hybrid (CD on FT) < CD < FT < hybrid (FT on CD). It is noticed that hybrid (CD on FT) gel maintained extremely low friction and showed minimal wear. The effectiveness of biphasic lubrication was evaluated by biphasic finite element analysis. The importance of the load support by fluid phase at early stage and the surface lubricity after lowering of interstitial fluid pressure in poly(vinyl alcohol) hybrid (CD on FT) gel are discussed by comparison of experiment and finite element analysis.