Therapeutic effect of HEVs in rat osteochondral defect model. (A) Macroscopic appearance of osteochondral defects at 6 weeks post-surgery. (B) The cross-section of micro-CT scan at the middle of defects. Scale bar = 1 mm. (C) Quantitative analysis of bone volume fraction (BV/TV), trabecular thickness (Tb.Th), trabecular separation (Tb.Sp), and trabecular number (Tb.N) of the regenerated subchondral bone. (D) Histological and immunohistochemical staining of the repaired cartilage. D with black arrows indicate defect areas. 150X magnification. Scale bar = 500 μm. (E) The modified O'Driscoll score for cartilage regeneration with three parameters, including nature of predominant tissue, structural characteristics, and freedom from degeneration. (F) Histological and immunohistochemical staining of synovial membrane. Red arrows indicate lining cell layers. Yellow boxes indicate synovial stromal with and without leukocytic infiltration (follicle-like aggregates). Black arrows indicate CD206 positive cells. Scale bar = 200 μm. (G) The synovitis score of synovial membrane with three parameters, including lining cell layer, stromal cell density, and inflammatory infiltrate. Data are presented as mean ± standard deviation, n = 6 per group. ^ denotes p < 0.05 compared to the SFM group; * denotes p < 0.05 compared to NEV group. @ denotes p < 0.05 compared to the NEV2 group.