Cell brick-enriched platelet-rich plasma gel guided chondrogenesis of bone marrow-derived mesenchymal stem cells. Examining chondrogenesis of grafts in vivo at 4 weeks (A to L) and 12 weeks (M to X). Merged images showed the B-CB-P and B-C-P groups acquired cell survival and tissue formation throughout the graft (A, E, M, Q), while the C-CB-P group accompanied central necrosis (U). The B-CB-P group presented chondrogenic differentiation in BMSC regions, as confirmed by hematoxylin and eosin (HE), Safranin-O and COL-II immunostaining (B, C, D; N, O, P), which is close to tissue formation from chondrocyte transplantation (V, W, X). In contrast, progressive osteogenesis occurred in the B-C-P and B-P groups (F, G, H; R, S, T; J, K, L); bar = 2 mm, magnification × 40 (A, E, M, Q, U); bar = 1 mm, magnification × 40(I); bar = 50 μm, magnification × 200 (B, C, D, F G, H, J, K, L, N, O, P, R, S, T, V, W, X). B-C-P, BMSCs–chondrocytes–PRP; B-CB-P, BMSCs–cell bricks–PRP; B-P, BMSCs–PRP; BMSC, bone marrow-derived mesenchymal stem cell; COL, collagen; PRP, platelet-rich plasma.