Three-Dimensional-Printed Gelatin Methacryloyl Scaffold Loaded with Extracellular Vesicles Derived from H₂S Preconditioned Mesenchymal Stromal Cells Promotes Neuronal Regeneration in Rats with Spinal Cord Injury

Background: spinal cord injury (SCI) causes irreversible motor and sensory deficits with limited effective treatments. Mesenchymal stromal cells (MSCs) exert therapeutic effects largely through extracellular vesicles (EVs). Preconditioning MSCs with a hydrogen sulfide (H 2 S) donor enhance the therapeutic potential of EVs. Objective: this study is aimed to develop a 3D-printed gelatin methacryloyl (GelMA) scaffold loaded with H 2 S-preconditioned MSC-derived EVs (H 2 S-EVs) to promote motor function recovery in SCI. Methods: H 2 S-EVs were isolated from NaHS (an H 2 S donor)-preconditioned MSCs and incorporated into a 3D-printed GelMA scaffold (3D/GelMA/EVs). Scaffold mechanical properties and H 2 S-EVs. The scaffold’s therapeutic efficacy was evaluated in a rat SCI model. Results: MiRNA microarray revealed miR-7a-5p as the most upregulated miRNA in H 2 S-EVs. The 3D/GelMA/EVs scaffold exhibited an appropriate elastic modulus and porous structure, enabling sustained local EVs release. In vivo, the scaffold significantly improved motor function recovery in SCI rats. Conclusion: these results indicated that H 2 S-EVs provided an important therapeutic tool against SCI by miR-7a-5p and 3D/GelMA/EVs scaffolds were ideal biomaterials for the intervention of SCI.