Biomimetic Bilayer Hydrogel for Scar-Minimizing Healing of Deep Second–Degree Burns Through Sequential Macrophage–Fibroblast Intervention

During the inflammatory phase, the persistent macrophage-mediated inflammatory response, followed by excessive fibroblast activation in the proliferative phase, impairs the repair of deep partial-thickness burn wounds and contributes to scar formation. Hence, precise spatiotemporal regulation of both macrophages and fibroblasts is of paramount importance. In this study, we developed a structurally biomimetic bilayer hydrogel system designed to promote scar-minimizing burn wound healing by sequentially targeting macrophages in the inflammatory phase and modulating fibroblast behavior in the proliferative phase. This biomimetic bilayer hydrogel (designated BHM@VP@PPs) consists of a lower layer (LHM) loaded with PBA-PEI@siRNA (TNF-α) nanocomplexes (LHM@PPs) and an upper layer (HHM) encapsulating the small-molecule YAP inhibitor verteporfin (HHM@VP). By varying the HM polymer concentration and crosslinking density, the bilayer hydrogel was designed to provide degradation-dependent, stage-matched release of siRNA and VP. During the inflammatory phase, released siRNA silenced TNF-α via blockade of its mRNA expression, thereby attenuating local inflammation and accelerating the transition to the proliferative phase. Upon degradation of the lower layer, the upper layer subsequently released VP, which suppressed excessive fibroblast activation through YAP-related signaling pathways during the proliferative phase, thus favoring scar-minimizing healing. Moreover, VP-mediated photodynamic therapy (PDT) generated abundant reactive oxygen species (ROS), effectively eradicating bacteria and preventing infection. Collectively, this bilayer hydrogel system synergistically facilitates scar-minimizing repair of deep second-degree burn wounds, offering a promising therapeutic strategy for clinical translation.