A novel adhesive dual-sensitive hydrogel for sustained release of exosomes derived from M2 macrophages promotes repair of bone defects.

The repair of bone defects remains a huge clinical challenge. M2 macrophage-derived exosomes (M2-Exos) can act as immunomodulators to promote fracture healing; however, how to retain the sustained release of exosomes to the target area remains a challenge. Here, we report a composite hydrogel loaded with M2-Exos aiming to accelerate bone defect healing. It was verified that the F127/HA-NB hydrogel had a dense network structure, tissue adhesiveness, and dual sensitivity to temperature and light. F127/HA-NB loaded with M2-Exos (M2-Exos@F127/HA-NB) exhibited good biocompatibility and achieved sustained release of exosomes for up to two weeks. The study showed that both M0-Exos and M2-Exos@F127/HA-NB significantly promoted osteogenic differentiation of rat bone marrow mesenchymal stem cells. The mechanism study implied that M2-Exos activates the Wnt/β-catenin signaling pathway to promote osteogenic differentiation of BMSCs. Finally, we evaluated the osteogenetic effects of M2-Exos@F127/HA-NB in a rat cranial defect model, and the results showed that M2-Exos@F127/HA-NB had superior bone regeneration-promoting effects. This study provides a new strategy for cell-free treatment of bone defects.