3-Dimensional Bioprinting of a Tendon Stem Cell-Derived Exosomes Loaded Scaffold to Bridge the Unrepairable Massive Rotator Cuff Tear.

BACKGROUND: Unrepairable massive rotator cuff tears (UMRCTs) are challenging to surgeons owing to the severely retracted rotator cuff musculotendinous tissues and extreme defects in the rotator cuff tendinous tissues. PURPOSE: To fabricate a tendon stem cell-derived exosomes loaded scaffold (TSC-Exos-S) and investigate its effects on cellular bioactivity in vitro and repair in a rabbit UMRCT model in vivo. STUDY DESIGN: Controlled laboratory study. METHODS: TSC-Exos-S was fabricated by loading TSC-Exos and type 1 collagen (COL-I) into a 3-dimensional bioprinted and polycaprolactone (PCL)-based scaffold. The proliferation, migration, and tenogenic differentiation activities of rabbit bone marrow stem cells (BMSCs) were evaluated in vitro by culturing them in saline, PCL-based scaffold (S), COL-I loaded scaffold (COL-I-S), and TSC-Exos-S. In vivo studies were conducted on a rabbit UMRCT model, where bridging was repaired with S, COL-I-S, TSC-Exos-S, and autologous fascia lata (FL). Histological and biomechanical analyses were performed at 8 and 16 weeks postoperatively. RESULTS: TSC-Exos-S exhibited reliable mechanical strength and subcutaneous degradation, which did not occur before tissue regeneration. TSC-Exos-S significantly promoted the proliferation, migration, and tenogenic differentiation of rabbit BMSCs in vitro. In vivo studies showed that UMRCT repaired with TSC-Exos-S exhibited significant signs of tendinous tissue regeneration at the bridging site with regard to specific collagen staining. Moreover, no significant differences were observed in the histological and biomechanical properties compared with those repaired with autologous FL. CONCLUSION: TSC-Exos-S achieved tendinous tissue regeneration in UMRCT by providing mechanical support and promoting the trend toward tenogenic differentiation. CLINICAL RELEVANCE: The present study proposes a potential strategy for repairing UMRCT with severely retracted musculotendinous tissues and large tendinous tissue defects.

Three-Dimensional Bioprinting of a Structure-, Composition-, and Mechanics-Graded Biomimetic Scaffold Coated with Specific Decellularized Extracellular Matrix to Improve the Tendon-to-Bone Healing.

Healing of a damaged tendon-to-bone enthesis occurs through the formation of fibrovascular scar tissue with greatly compromised histological and biomechanical properties instead of the regeneration of a new enthesis due to the lack of graded tissue-engineering zones in the interface during the healing process. In the present study, a structure-, composition-, and mechanics-graded biomimetic scaffold (GBS) coated with specific decellularized extracellular matrix (dECM) (GBS-E) aimed to enhance its cellular differentiation inducibilities was fabricated using a three-dimensional (3-D) bioprinting technique. In vitro cellular differentiation studies showed that from the tendon-engineering zone to the bone-engineering zone in the GBS, the tenogenic differentiation inducibility decreased in correspondence with an increase in the osteogenic differentiation inducibility. The chondrogenic differentiation inducibility peaked in the middle, which was in consistent with the graded cellular phenotypes observed in a native tendon-to-bone enthesis, while specific dECM coating from the tendon-engineering zone to the bone-engineering zone (tendon-, cartilage-, and bone-derived dECM, respectively) further enhanced its cellular differentiation inducibilities (GBS-E). In a rabbit rotator cuff tear model, histological analysis showed that the GBS-E group exhibited well-graded tendon-to-bone differentiated properties in the repaired interface that was similar to a native tendon-to-bone enthesis at 16 weeks. Moreover, the biomechanical properties in the GBS-E group were also significantly higher than those in other groups at 16 weeks. Therefore, our findings suggested a promising tissue-engineering strategy for the regeneration of a complex enthesis using a three-dimensional bioprinting technique.