Janus Hydrogel to Mimic the Structure and Property of Articular Cartilage

Designing hydrogels with adequate strength, remarkable swelling resistance, low friction coefficient, excellent biocompatibility, and osseointegration potential is essential for replacing articular cartilage. However, it remains challenging to integrate all these properties into one material. In this work, a Janus hydrogel was prepared from polyvinyl alcohol, chitosan, and sodium hyaluronate, followed by a one-sided dipping in situ precipitation mineralization to form a layer of hybridized hydroxyapatite (HAp), wherein the two surfaces had distinct compositions and functions. Because of the negative carboxyl groups from sodium hyaluronate, the top surface possessed a friction coefficient as low as 0.024. On account of the HAp mineralized layer, the bottom side had osteogenesis potential. Owing to the synergy of physical linkages, the hydrogel displayed compressive strength as high as 78 MPa. Furthermore, it demonstrated remarkable swelling resistance with strength retention near 100% even after soaking in PBS solution at 37 °C for 7 days. The absence of toxic chemicals maintained the merits of starting polymers and resulted in excellent biocompatibility (cell viability ≈ 100%), making it an ideal substitute for articular cartilage.