Histological photographs of the representative cartilage tissues in four groups with safranin-O staining. Surface regularities and arranged chondrocytes were found in SED group (A). However, surface irregularities, cell cloning and moderate reduction in the safranin-O staining were detected in the HIR group (B). Smooth surface, disarranged chondrocytes and reduction in the safranin-O staining were displayed in HIRI group (C). Compared with the HIRI1 group, lesser reduction in Safranin-O staining was detected in the HIRI2 group (D). scale bar = 50 μm.