Functionally graded bilayer polyurethane sponge with sequential stage-adaptive capabilities for full-cycle repair of...

The management of full-thickness infected wounds remains a major clinical challenge, largely due to the paucity of multifunctional dressings capable of stage-adaptive regulation across the entire healing cascade. To address this need, we developed a functionally graded bilayer polyurethane composite sponge. The upper layer was fabricated by chemical foaming combined with dopamine-assisted reduction, producing a hydrophobic macroporous sponge bearing a polydopamine coating and loaded with silver nanoparticles (PUF@P-Ag). The lower layer was a hydrophilic microporous polyurethane sponge (PUS) prepared by freeze-drying, which provided rapid hemostasis and controllable degradability. During the hemostatic phase, the PUS layer concentrated blood components to promote efficient clot formation and subsequently underwent rapid degradation. In the inflammatory phase, the acidic microenvironment generated by PUS degradation acted synergistically with sustained silver ion release from the upper layer and near-infrared photothermal effects, thereby establishing a triple antibacterial system. Concurrently, the polydopamine coating alleviated local oxidative stress. As healing progresses into the proliferation phase, a sustained weakly acidic milieu supported endothelial cell proliferation and angiogenesis. In a rat model of full-thickness infected skin defects, the bilayer sponge demonstrated sequential functional switching and synergistic activity, significantly accelerating wound closure, and promoting tissue remodeling and neovascularization.