Abstract: Objective To assess the efficacy of GelMA hydrogel loaded with bone marrow stem cell-derived exosomes for repairing injured rat knee articular cartilage. Methods The supernatant of cultured bone marrow stem cells was subjected to ultracentrifugation separate and extract the exosomes, which were characterized by transmission electron microscopy, particle size analysis and Western blotting of the surface markers. The changes in rheology and electron microscopic features of GelMA hydrogel were examined after loading the exosomes. We assessed exosome release from the hydrogel was detected by BCA protein detection method, and labeled the exosomes with PKH26 red fluorescent dye to observe their phagocytosis by RAW264.7 cells. The effects of the exosomes alone, unloaded hydrogel, and exosome-loaded hydrogel on the polarization of RAW264.7 cells were detected by q-PCR and immunofluorescence assay. We further tested the effect of the exosome-loaded hydrogel on cartilage repair in a Transwell co-culture cell model of RAW264.7 cells and chondrocytes in a rat model of knee cartilage injury using q-PCR and immunofluorescence assay and HE and Masson staining. Results GelMA hydrogel loaded with exosomes significantly promoted M2-type polarization of RAW264.7 cells (P<0.05). In the Transwell co-culture model, the exosome-loaded GelMA hydrogel significantly promoted the repair of injured chondrocytes by regulating RAW264.7 cell transformation from M1 to M2 (P<0.05). HE and Masson staining showed that the exosome-loaded hydrogel obviously promoted cartilage repair in the rat models damage. Conclusion GelMA hydrogel loaded with bone marrow stem cell-derived exosomes can significantly promote the repair of cartilage damage in rats by improving the immune microenvironment.

Key words: GleMA hydrogel; cartilage damage; exosomes; immunoregulation