Effects of nicotine on the repair of the cartilage defect with BMSCs transplantation in a rat model after 12 weeks. a and b Macroscopic observation of cartilage repair (×100). c Macroscopic scores of cartilage repair. d and e Safranin-O and fast green staining of cartilage repair (×100). f Histological scores of cartilage repair. Data represent mean ± SD (n = 8). *p < 0.05. Scale bar = 200 μm. BMSCs bone marrow mesenchymal stem cells.