Histological photographs of the representative repair tissues of defects in four groups at 14 weeks after operation with safranin-O staining.

<p>(A–B) Fibrocartilaginous tissue in SED group. The extracellular matrix was poorly organized. (C–D) Fibrocartilaginous tissue in 2W group. The partly filled defect. The margin of the normal cartilage adjacent the defect is destroyed. (E–F) Repair tissue in 4W group. A large number of rounded cells embedded in the intensely Safranin-O stained extracellular matrix. The integration of the lesion to adjacent articular cartilage is good. (G–H) Regenerative tissue in 8W group. The surface of the repair tissue is irregular. The bonding area is acellular. Fig. B, D, F, H (scale bar = 200 µm) are higher magnifications of the junction of the repair tissue and the residual cartilage from Fig. A, C, E, G (scale bar = 500 µm) respectively. SC: surrounding cartilage. →: defect margin.