Representative toluidine blue staining of the sections in experimental group (A, C) and control group (B, D) at 4 weeks. (A) Slightly stained repair tissue (R) covered more than 50% of the cartilage defect, although the surface was not smooth. At higher magnification (C), Toluidine blue staining of repair tissue (R) near native cartilage (C) was intense, and the integration was good. No tidemark formation was observed. (B) Negatively stained repair tissue (R) covered less than 50% of the cartilage defect. At higher magnification (D), only fibrous tissue was observed in the defect, and no tidemark formation was found. The left column images are magnified 20X, the right column images are magnified 100X.