Strong and tough hydrogel with hierarchical ordered architecture and gradient composition based on biomimetic natural cartilage

Hydrogels are ideal materials for biomimetic soft tissues due to their excellent biocompatibility and hydrophilicity. Inspired by the hierarchical structure of natural cartilage, we propose a biomimetic strategy of "hierarchically ordered architecture co gradient composition", creating a trilayer heterogeneous biomimetic cartilage hydrogel with synergistically enhanced load-bearing and lubrication functionalities, by using magnetic and temperature fields to induce ordered hydrogel networks and applying dispersion strengthening and nano-reinforcement. Specifically, the superficial layer with horizontally oriented graphene oxide (GO) nanosheets provides a shear-resistant network and low friction, the intermediate layer, featuring interwoven molecular chains and high-strength carbon fibers (CF), and the deep layer, with vertically oriented networks reinforced by hydroxyapatite (HA), collectively provide robust compressive strength of approximately 13.8 MPa at 50% strain. The friction coefficient of natural cartilage/trilayer heterogeneous biomimetic cartilage is only 0.023. The exceptional combination of high load-bearing and low friction arises mainly from interlayer heterogeneity and hydration lubrication. This work offers a novel approach for optimizing both mechanical and tribological properties of hydrogel materials.