Rocket propulsion-inspired two-stage nitric oxide-releasing hydrogel for phase-matched therapy of diabetic wounds

The healing of diabetic foot ulcers (DFUs) is critically impaired by a self-perpetuating cycle of bacterial infection and chronic inflammation, rendering single-phase therapeutic strategies ineffective. To dynamically address these distinct pathological challenges, we designed a sequentially acting nitric oxide (NO)-releasing hydrogel inspired by the stage-separation principle of rocket propulsion. The hydrogel, formed by crosslinking NO-loaded polyethyleneimine (PEI-NO) with oxidized hyaluronic acid, provides a sharp initial NO release (Stage I). A subsequent sustained release phase (Stage II) is achieved through the combined contribution of residual PEI-NO and encapsulated S-nitrosated cholesterol liposomes (Lip-SNO), with the kinetics tunable via the PEI-NO/Lip-SNO ratio. In vivo experiments demonstrated that this sequential release profile drove a biphasic healing response: the initial NO burst eradicated bacteria and quelled early inflammation, while the sustained NO release during the later stage continuously improved the wound immune microenvironment, promoted macrophage polarization toward the M2 phenotype, increased vascular endothelial growth factor expression, enhanced angiogenesis, and facilitated collagen deposition and tissue remodeling. Consequently, this two-stage sequential release strategy significantly accelerated wound closure in a DFU model, indicating that precise temporal control of NO dosage and release profiles according to disease stage represents an effective strategy for precision therapy of DFU wounds. STATEMENT OF SIGNIFICANCE: Infected diabetic foot wounds are complex chronic conditions for which current treatments mainly rely on antibiotics and local wound management; however, their therapeutic efficacy is often limited by insufficient drug penetration, infections caused by drug-resistant bacteria, and the difficulty of resolving persistent inflammation. Nitric oxide (NO), owing to its broad-spectrum antibacterial activity, immunomodulatory effects, and ability to promote angiogenesis and tissue regeneration, has shown considerable potential in the treatment of diabetic wounds. Nevertheless, diabetic wound healing is highly stage dependent, and material systems capable of delivering NO in a manner matched to disease progression remain insufficiently explored. To address this challenge, this study proposes a rocket-inspired, stage-matched NO delivery strategy and develops a lipid hydrogel system with sequential NO release to achieve precise regulation and synergistic therapy across different healing stages of infected diabetic foot wounds.