Bilayered laponite/alginate-poly(acrylamide) composite hydrogel for osteochondral injuries enhances macrophage polarization: An in vivo study

Addressing osteochondral defects, the objective of current study was to synthesize bilayered hydrogel, where the cartilage layer was formed by alginate (Alg)-polyacrylamide (PAAm) with and without the addition of TGF-β3 and bone layer by laponite XLS/Alg-PAAm and characterize by in vitro and in vivo experiments. Exceeding the mechanical strength of Alg-PAAm (32.95 ± 1.23 kPa) and XLS based (317.5 ± 21.72 kPa) hydrogels, XLS/Alg-PAAm hydrogel (469.7 ± 6.1 kPa) activated macrophages towards M2 phenotype and stimulated the expression of anti-inflammatory factors. The addition of TGF-β3 accelerated transition of macrophage polarization, especially between day 4 and 7. The expression levels of M1-related genes such as CD80, iNOS and TNF-α decreased gradually after day 4, reaching lowest values at day 13, whereas the expression levels of M2-related genes, CD206, Arg1 and STAT6 significantly increased promoting M2 macrophage polarization, which might be associated with accelerated bone repair. Moreover, bilayer structure exhibited a better cell viability as well as repairment thorough the XLS contents. In vivo histological examinations verified the significant surface regularity and hyaline like tissue formation employment, along with synchronized degradation profile of the hydrogel with tissue healing at the end of 12 weeks. A mechanically durable, biocompatible and immunocompatible hydrogel was formulated to be utilized in bone-cartilage engineering applications. • Implantable biomaterials have emerged as critical solutions for osteochondral defects. • A bilayered laponite/alginate-poly(acrylamide) composite hydrogel is formulated. • The mechanical property is significantly improved by laponite XLS. • The transition of macrophage polarization accelerated to the reparative M2 phase. • The repair of articular cartilage and subchondral bone is enhanced.