Nano-hydroxyapatite enhanced double network hydrogels with excellent mechanical properties for potential application in cartilage repair

Hydrogels with desirable characteristics have been supposed to be potential materials for cartilage repair. However, the biomechanical, biotribological and biocompatible properties of hydrogels remain some crucial challenges. To address these challenges, we developed a dual physically cross-linked poly (vinyl alcohol)-(nano hydroxyapatite)/(2-hydroxypropyltrimethyl ammonium chloride chitosan) (PVA-HA/HACC-Cit) hydrogels with double-network (DN) through a simply freezing/thawing technique and an immersing process. The DN hydrogel with an optimized HA concentration exhibited outstanding fracture tensile stress (2.70 +/- 0.24 MPa), toughness (14.09 +/- 2.06 MJ/m(3)) and compressive modulus (0.88 +/- 0.09 MPa). In addition, the PVA-HA/HACC-Cit DN hydrogels demonstrated remarkable anti-fatigue property, extraordinary self-recovery and energy dissipation ability due to their unique dual physically cross-linked structures. Moreover, the low friction coefficient, the predominant wear resistance property, as well as the excellent cytocompatibility were realized for the DN hydrogels because of the existence of nano-hydroxyapatite. Thus, this work puts forward a new strategy in the preparation of DN hydrogels for promising applications in cartilage repair.