Dual-physical network PVA hydrogel commensurate with articular cartilage bearing lubrication enabled by harnessing nanoscale crystalline domains

Hydrogel, as one of potential soft materials for articular cartilage, has encountered pressing obstacles, such as insufficient mechanical properties, poor lubrication, and easy to wear. To tackle these, we propose a strong yet slippery polyvinyl alcohol/chitosan (PVA/CS) hydrogel with dual-physically crosslinked networks by harnessing freeze-thawing, salting-out, annealing, and rehydration. High mechanical properties of PVA/CS hydrogel can be readily regulated by adjusting proportion of PVA/CS and annealing temperature. The optimized hydrogel exhibits high mechanical properties with tensile strength of ~ 19 MPa at strain of 550%, compression strength of ~ 11 MPa at small strain of 39%, and outstanding toughness and anti-fatigue owing to the robust physical interactions, including hydrogen bonds, crystallization, and ionic coordination. Moreover, the equilibrium hydrogel shows low friction coefficient of ~ 0.05 against Al₂O₃ ball under the condition of 30 N, 1 Hz, with water as the tribological medium, which is close to the lubrication performance of native cartilage. And meanwhile, the proposed cartilage-like slippery hydrogel displays stable long-term lubrication performance for 1 × 10⁵ reciprocating cycles without destructive wear and structure damage. It is therefore believed that the biocompatible cartilage-like slippery hydrogel opens innovative scenarios for developing cartilage-mimicking water-lubricated coating and biomedical implants with satisfactory load-bearing and lubrication performance.