swelling of low-friction, high load-bearing self-bending bilayer hydrogels inspired by articular cartilage.

The articular cartilage is characterized by its gradient hierarchical structure, which exhibits excellent lubrication and robust load-bearing properties. However, its inherent difficulty in self-repair after damage presents numerous formidable challenges for cartilage repair. Inspired by the unique structure of articular cartilage, a biomimetic bilayer hydrogel composed of PAM (polyacrylamide) and PAM/SA (sodium alginate) is prepared using a two-stepswelling method. The bilayer hydrogel demonstrates exceptional structural stability due to the interlayerchemical cross-linking. Compared to monolayer hydrogels, the PAM-PAM/SA bilayer hydrogel demonstrates superior mechanical attributes, exhibiting a compressive strength of 1 MPa and a compressive modulus of 0.22 MPa. Furthermore, exploration of the tribological performance of the PAM-PAM/SA bilayer hydrogel have revealed its low-friction performance under high loads, with a coefficient of friction as low as 0.032. Finally, leveraging the differential swelling properties between the distinct layers of the PAM-PAM/SA bilayer hydrogel, a self-bending biomimetic cartilage capable of conforming to complex joint surfaces is fabricated. This highly lubricating, mechanically robust, and conformal biomimetic cartilage provides an effective means for addressing cartilage defects and joint diseases.