High‐Strength Poly(Vinyl Alcohol) Hydrogels for Artificial Cartilage

Physically cross-linked poly(vinyl alcohol) (PVA) gels are versatile biomaterials owing to their excellent biocompatibility and mechanical strength. Since the late 1970s, semicrystalline PVA gels prepared by a freeze–thawing method (FT gel) have been extensively studied in order to characterize their structural and functional properties for practical applications such as artificial hydrogel cartilage. A simple method to prepare a physically crosslinked PVA gel by a cast-drying method (CD gel), which was recently reported, is also promising, and PVA gels can be expected to be applied widely. Although the network nanostructures of the FT and CD gels are similar to each other, the CD gels are transparent and elastic, whereas the FT gels are opaque and less elastic. The crystallization conditions of these systems have been investigated, and both gels became highly swollen and rigid by selecting optimum preparation conditions. In this study, the mechanical properties of FT and CD gels, such as tearing energy, sliding friction, and abrasion loss, were investigated. On the basis of the experimental results, simple preparation methods to improve the mechanical properties of physically cross-linked PVA gels are discussed. Finally, recently introduced preparation methods of PVA gels intended for use as artificial hydrogel cartilage are presented by controlling the polymer networks of FT and CD gels on the nano- and microscales.