In Situ Cross-Linking of Poly(vinyl alcohol)/Graphene Oxide-Polyethylene Glycol Nanocomposite Hydrogels as Artificial Cartilage Replacement: Intercalation Structure, Unconfined Compressive Behavior, and Biotribological Behaviors

Poly(vinyl alcohol) (PVA)/graphene oxide (GO) nanocomposite hydrogel as artificial cartilage replacement was prepared via freezing/thawing method by introducing polyethylene glycol (PEG). Efficient grafting of PVA molecules onto GO surface was realized by formation of hydrogen bonding, resulting in exfoliation and uniform distribution of GO in PVA matrix. By introduction of appropriate content of GO, the increased crystalline regions of PVA and the formation of GO centered second network structure led to the increase of the storage modulus and effective cross-linking density. And therefore the mechanical strength and toughness of the composite hydrogel were improved simultaneously: the tensile strength, elongation at break, and compressive modulus showed approximately 200%, 40%, and 100% increase of the neat PVA hydrogel. Besides, for the sample with 1.5 wt % GO content, the maximum force retention and dynamic stiffness were improved remarkably in the process of sinusoidal cyclic compression, and the compressive relaxation stress also increased significantly, indicating the enhancement of the compressive recoverable and antifatigue ability, and resistance to compressive relaxation by formation of high load-bearing, dense, and reinforcing double network structure. Moreover, more than 50% decrease in coefficient of friction was obtained for the composite hydrogel, and the worn surface presented relative smooth and flat features with sharp decreasing furrow depth, confirming the lubrication effect of GO-PEG. This study shows promising potentials in developing new materials for cartilage replacement with simultaneous combination of high mechanical property and excellent lubrication.