Fig. 4

Histological analysis. a H&E staining. b Safranin O/fast green staining. H&E and safranin O/fast green staining showed that the normal group and iMSC-Exos group presented typical hyaline features with a smooth cartilage surface, regular cellular organization, and normal proteoglycan content. Compared with the iMSC-Exos group, the SMMSC-Exos group showed moderate surface irregularity, superficial fibrillation, and a loss of proteoglycan (reddish-orange stain). c OARSI scores in the normal, iMSC-Exos, and SMMSC-Exos groups were significantly lower than in the OA group. The score of the iMSC-Exos group was significantly lower than the SMMSC-Exos group, while there was no significant difference between the iMSC-Exos group and the normal group. *P < 0.05. iMSC-Exos exosomes secreted by induced pluripotent stem cell-derived mesenchymal stem cells, OA osteoarthritis, OARSI Osteoarthritis Research Society International, SMMSC-Exos exosomes secreted by synovial membrane mesenchymal stem cells