Effect of the migrated human MSCs on the healing of an osteochondral defect. (a) Histological findings of the defect from Safranin-O staining. Bar = 1 mm. (b) ICRS macroscopic score of each group. Bars represent the mean ± SD of the score. n = 3, *P < 0.05, **P < 0.01, NS = not significant. HCF, heparin-conjugated fibrin; HD, high dose; ICRS, International Cartilage Repair Society; LD, low dose; MSC, mesenchymal stem cell; PDGF, platelet-derived growth factor; TGF-β, transforming growth factor-β