Size-Tunable Positively Charged Methacrylated Gelatin/Chitosan Composite Hydrogel Microspheres Promote Angiogenesis.

Angiogenesis is a fundamental prerequisite for functional tissue regeneration, and biomaterials that drive endogenous vascularization hold immense translational potential for treating tissue defects, organ damage, and ischemic diseases. Herein, gelatin methacryloyl (GelMA) and chitosan methacryloyl (CSMA) were synthesized via a copolymerization-based modification method. Hydrogel microspheres were prepared by emulsification, followed by cross-linking through photoinitiator-induced radical polymerization under UV light. Combined with freeze-drying, size-tunable porous GelMA/CSMA composite microspheres (G/CMS) were fabricated. The as-prepared G/CMS establish a favorable pro-regenerative microenvironment by integrating size-dependent mechanical feedback and charge-mediated cellular interactions. Specifically, CSMA incorporation imparted a positive surface charge, enhancing cellular affinity, while smaller diameters amplified mechanical stimuli promoting adhesion via mechanotransduction. In vitro, the optimized formulation (G/CMS-B) significantly promoted the proliferation, migration, and tube formation of human umbilical vein endothelial cells (HUVECs), and upregulated key angiogenic genes (VEGF, ANG, KDR) without exogenous growth factors. In vivo, subcutaneous implantation and hindlimb ischemia models confirmed accelerated neovascularization and blood flow recovery. The developed G/CMS exhibited excellent biocompatibility, controllable degradability, injectability, and excellent elastic recovery. This synergistic platform effectively modulates physicochemical cues to promote vascularization, offering a promising, cost-effective strategy for regenerative medicine.