Mechanistically Guided Design of Injectable Oxidized Alginate-Carboxymethyl Chitosan Hydrogel Composites with Neomycin-Loaded Gelatin Microspheres via a Crosslinking-Limited Regime for Antibacterial Wound Healing

Developing multifunctional hydrogel dressings remains a challenge in wound care. An injectable, self-crosslinking hydrogel composite based on oxidized alginate (OA) and carboxymethyl chitosan (CMCS) was developed via dynamic Schiff base reactions, with neomycin-loaded gelatin microspheres for sustained antibacterial delivery. The system exhibited excellent injectability, self-healing capability, and cytocompatibility. A key advancement is establishing a crosslinking-limited regime as a predictive design framework for OA-CMCS hydrogels through gelation kinetics and swelling analyses, enabling quantitative regulation of functional performance via OA/CMCS stoichiometry. An optimal ratio (OA/CMCS = 1.25-1.50) maximized network formation, supported by structural observations, degradation, and mechanical performance. Among formulations, hydrogels containing residual gel-like CMCS showed balanced performance, including enhanced mechanical strength, superior post-injection stability, favorable swelling behavior, and improved antibacterial efficacy and fibroblast migration. These advantages are attributed to pore-filling effect and secondary network-like reinforcement induced by residual CMCS within the hydrogel matrix. Furthermore, neomycin-loaded gelatin microspheres enabled a dual-stage antibacterial effect and contributed to mechanical reinforcement and accelerated gelation kinetics. Beyond advancing the fundamental understanding of dynamic polysaccharide hydrogel networks, the proposed OA-CMCS hydrogel composite provides a technologically scalable and clinically translatable strategy for engineering multifunctional wound dressings with tunable mechanical stability, antibacterial activity, injectability, and therapeutic performance.