Microneedle delivery of 3D bioprinted tendon stem/progenitor cells microfiber-derived extracellular vesicles enhances chronic massive rotator cuff tears healing.

High retear rates after surgical repair of chronic massive rotator cuff tears (CMRCT) are primarily due to the failure to regenerate native tendon tissue. Extracellular vesicles (EVs) derived from rat tendon stem/progenitor cells (rTSPCs) present substantial potential benefits for the treatment of CMRCT. However, the limited yield and efficacy of rTSPCs-EVs produced through traditional methodologies (2D-cultured) severely restrict their widespread application. In this study, we proposed an innovative strategy integrating 3D bioprinted rTSPCs microfiber-derived EVs production (3D-rTSPCs-EVs) introducing a novel therapeutic approach for CMRCT. In vitro comparison demonstrating that 3D-rTSPCs-EVs are significantly superior to rTSPCs-EVs in promoting tenogenic differentiation and exerting anti-inflammatory effects. Meanwhile, to overcome the issues of rapid clearance and low bioavailability associated with the direct injection of EVs, the Hyaluronic Acid Methacrylate-based microneedle (HAMA-MN) scaffold was designed for the local delivery of 3D-rTSPCs-EVs (3D-rTSPCs-EVs@MN) at the tendon-to-bone junction. Subsequently, in vivo 3D-rTSPCs-EVs@MN facilitated the regeneration of a native, collagen matrix-rich tendon tissue as evidenced by improved histological, radiologic manifestations and biomechanical function. Furthermore, 3D-rTSPCs-EVs suppressed the inflammatory response by regulating macrophage polarization from the pro-inflammatory M1 phenotype to the pro-healing M2 phenotype. Therefore, our findings suggest that 3D bioprinted rTSPCs-microfiber derived EVs significantly ameliorates scar tissue formation to enhance biomechanical properties of injured rotator cuff, opening new avenues for efficient EVs-based therapies in CMRCT treatment.