Tendon gel using the film model method promotes ligament healing in rabbits

Tendon gel is a translucent gel-like material secreted from the ends of a severed tendon. When mechanical stress is applied to a 3-day in vivo-preserved tendon gel, it matures into type I collagen–dominant tissue similar to normal tendon. This study aimed to evaluate the effects of transplanting a 3-day in vivo-preserved tendon gel into a knee medial collateral ligament (MCL) injury site in rabbits to promote intrinsic ligament regeneration. Tendon gel was prepared from rabbit Achilles tendons using the film model method and harvested after 3 days of in vivo preservation. The 3-day tendon gel was transplanted into the knee MCL injury sites in another set of rabbits (n = 48). Additionally, the healing process was assessed at 1, 2, and 4 weeks postoperatively using mechanical and histological analyses. Ultimate load, peak stress, and elastic modulus were measured. Histological maturity was semi-quantitatively scored, and collagen type I and III expressions were examined by immunofluorescence staining. At 2 weeks, the tendon gel group demonstrated significantly higher ultimate load than the control group (12.25 ± 4.90 vs. 5.25 ± 2.40 N; p = 0.02). The tendon gel group had greater peak stress than the control group (3.54 ± 1.44 vs. 1.69 ± 0.78 MPa; p = 0.02). Histological scores were higher in the tendon gel group than in the control group (7.25 ± 0.43 vs. 5.50 ± 1.73; p = 0.03). Cells in the tendon gel group were aligned parallel to collagen fibers with elongated nuclei, while type I collagen expression was stronger than that observed in controls. Transplanting a 3-day in vivo-preserved tendon gel into an injured ligament enhanced mechanical strength and histological maturation at 2 weeks postoperatively. These findings suggest that this tendon gel serves as a promising biomaterial for accelerating ligament healing.