Evaluation of influence of changes in permeability with aging on friction and biphasic behaviors of artificial hydrogel cartilage

Various hydrogels have been developed to use as artificial cartilage. Poly(vinyl alcohol) (PVA) hydrogel cross-linked by hydrogen bonds is biocompatible and has similar properties to natural articular cartilage. For clinical use as artificial cartilage, superior tribological performance with low friction and minimal wear are required. In our previous study, three kinds of preparation methods for PVA hydrogels with high water content, i.e., the repeated freeze-thawing (FT) method, the cast-drying (CD) method and the layered hybrid method composed of FT and CD layers were applied. As hybrid gel specimens, (CD on FT) and (FT on CD) gels were prepared. The comparison between experiment and biphasic finite element analysis showed that the frictional behaviors of these PVA hydrogels at slow speed are controlled by their biphasic lubrication mechanism. After that, it was found that the biphasic properties of FT gel with heterogeneous network structure was largely changed after immersion in water for more than 6 years. In this paper, the influence of changes in permeability with aging of FT gel on friction and biphasic behaviors of PVA hydrogels was evaluated by biphasic finite element analysis. As aged FT specimens with lower permeability, four kinds of aged FT specimens with different elastic properties were evaluated. As a result, it is suggested that frictional behavior of PVA FT gels with aging can be improved by lowering of permeability in aged FT gel. Furthermore, it is expected that hybrid gel as CD on aged FT with appropriate elastic modulus can sustain superior low friction.