Injectable thermosensitive hydrogel incorporating exosome-loaded chitosan microspheres for immunomodulation and cartilage regeneration.

Background: Chronic inflammation and impaired immune microenvironment are key barriers to effective cartilage regeneration. Herein, we developed an integrated, injectable thermosensitive hydrogel system termed CS@Gel-Mg. This system modularly combines exosome-loaded chitosan microspheres (CM@Exo)​ embedded within a Mg Methods: Hydroxypropyl-modified chitosan microspheres were synthesized via emulsion crosslinking and effectively loaded with bioactive exosomes. The Gel matrix was fabricated using an ionic liquid monomer (IL-C4) copolymerized with NIPAM and N-vinylimidazole, followed by Mg Results: In vitro, the system demonstrated excellent cytocompatibility, promoted ATDC5 cell proliferation and migration, and inhibited apoptosis. The hydrogel also reprogrammed macrophage polarization from M1 to M2 phenotype, as confirmed by qPCR and flow cytometry. In vivo, using a rat full-thickness cartilage defect model, CS@Gel-Mg exhibited improved weight-bearing function, reduced inflammatory infiltration, and superior cartilage histological scores compared to control groups. Mechanistically, immunofluorescence and Western blot analyses suggested enhanced expression of SOX9, COL2A1 and COL1A1, along with suppression of inflammatory cytokines. Furthermore, SOX9 knockdown in vivo diminished the therapeutic effect, confirming its regulatory role in the immuno-chondrogenic axis. Conclusion: This exosome-integrated thermoresponsive hydrogel provides a multifunctional platform for immune modulation and cartilage regeneration. Our findings highlight the potential of CS@Gel-Mg as a promising therapeutic strategy for osteochondral repair.