Human Tendon-Derived Hydrogel Improves Healing of Chronic Tendon–Bone Interface Injuries

Abstract

Grant support received from: 2016 AFSH Basic Science Grant There is no financial information to disclose. Previously our laboratory reported the positive impact of thermoresponsive, type 1 collagen–rich, decellularized human tendon-derived hydrogel (tHG) on tendon healing using a rat Achilles tendon acute injury model. We hypothesized tHG would facilitate healing of chronic injuries at tendon–bone interface (TBI) in a rotator cuff model. Rotator cuff tears are important causes of pain and disability of upper extremity and involve injury at TBI. In this study a rat chronic rotator cuff injury model was used to evaluate TBI healing after repair. Twenty Sprague–Dawley rats underwent bilateral detachment of supraspinatus (SSp) tendons. Eight weeks later, both SSp tendons were anatomically reattached to humerus. One shoulder underwent a suture to bone repair using bone tunnels (control group, n = 20) and the other underwent the same repair plus tHG injection at repair site (tHG group, n = 20). Eight weeks after repair, SSp tendon–muscle units with humeral bone were harvested after animal death. Biomechanical tests were performed on 15 samples in each group. Five additional samples in each group were evaluated via micro CT, followed by histological examinations. Paired t tests were performed for statistical analyses. Biomechanical testing revealed significantly larger load to failure (27.5 ± 11.8N vs 19.7 ± 5.4N, P = .03) and higher stiffness (15.7 ± 6.3 N/mm vs 11.5 ± 3.5 N/mm, P = .02) in the tHG group versus control. Safranin O staining showed the significantly larger area of new cartilage formation in the tHG group (0.48 ± 0.1 mm2 vs 0.32 ± 0.06 mm2, P = .03). Based on birefringence under polarized microscopy in Picosirius red–stained slides collagen fiber organization was greater in tHG group compared with the control (40.4 ± 9.8 gray scale vs 31.1 ± 4.2 gray scale, P = .07), although it did not significantly differ. Micro CT demonstrated higher bone mineral density (296.1 ± 21.9 mg/cm3 vs 274.6 ± 17.2 mg/cm3, P = .05) and larger trabecular number (1.7 ± 0.1/mm vs 1.5 ± 0.2, P = .07) at the supraspinatus insertion area of the humerus in tHG group than those in the control, although the difference did not reach statistical significance. •Injection of collagen-rich tHG at the rotator cuff repair site statistically significantly enhanced biomechanical properties and increased fibrocartilage formation at the TBI in a chronic injury model.•An improvement collagen fiber organization, higher bone mineral density, and larger trabecular number were also seen in the tHG group versus control.•This human-derived collagen gel is a promising scaffold to augment healing of chronic TBI injuries during surgical intervention. This research was supported by a Basic Science Grant from the American Foundation for Surgery of the Hand.