**Abstract**

This rabbit animal study has a hypothesis that the collagen gel, which is injectable easily, can be an effective carrier for recombinant human bone morphogenetic protein 2 (rhBMP-2) for the tendon healing in a bone tunnel. The cut upper long digital extensor tendon of each rabbit was inserted into the proximal tibia bone tunnel, and rhBMP-2 conjugated collagen gel was injected into the tendon-bone tunnel interface using a syringe. Biomechanical and histological performances were analyzed at 3 and 6 weeks after surgery. The collagen sol at room temperature was transformed to a gel at 37°C. The rhBMP-2 was slowly released from the collagen gel for more than 4 weeks. The in vivo experiment showed the enhanced new fibrocartilage and bone tissue formation at 6 weeks after injecting the rhBMP-2-containing collagen gel. The calcification and enthesis-like tissue were detected radiologically in the repaired tendon-bone junction. The viscous collagen gel-containing rhBMP-2 increased the fusion rate of the repaired tendon in the bone tunnel. This study showed that viscous collagen gel can be an effective carrier for rhBMP-2 for tendon healing in the bone tunnel. The rhBMP-2-containing collagen gel will be promising for tendon-bone interface healing in the future.

**Keywords:** rhBMP-2, tendon, bone tunnel, enthesis, ligament injury
