Articular cartilage defects in a rat model and gross appearance and scoring result at 16 weeks post-transplantation. (A) Gross photos of articular cartilage defects in a rat model. A) The patella was laterally dislocated and full-thickness articular cartilage defects (2 mm diameter) were created through subchondral bone in the trochlear groove in each hindlimb. B) After removing cartilage and bone debris, composites of hUCB-MSCs and different hydrogels were transplanted into defects. (B) Gross findings of repair tissue at articular cartilage defects in rat knees. At 16 weeks postoperatively, tissue defects in hUCB-MSC transplanted knees were repaired to almost the normal level, and border regions between repair and normal tissue were less distinct than those in corresponding control knees. No significant macroscopic differences were observed between the four different hydrogel groups. (C) Gross appearance scores of experimental and control knees in four different hydrogel groups (n = 5/group, *P <0.05).