Enzyme-crosslinked protocatechualdehyde acetal-modified polyvinyl alcohol hydrogel with acid-responsive and emerging photothermal properties for infected skin wound management

External pathogens and underlying diseases often complicate the wound microenvironment and hinder healing. The combination of plant polyphenols and photothermal therapy offers multiple advantages for skin wound repair and represents a promising alternative to conventional antibiotics. However, most plant polyphenols are susceptible to chemical degradation and inherently lack photothermal responsiveness. In this study, protocatechualdehyde (PA), a plant polyphenol with diverse bioactivities, was selected. Polyvinyl alcohol (PVA) was modified through acetalization with PA to obtain polyvinyl protocatechualdehyde acetal (PPA). Subsequently, the catechol groups of PA were enzymatically cross-linked using HRP/H₂O₂ to form a hydrogel. This acetal-grafting strategy not only shielded the functional groups of PA from excessive degradation, but also conferred acid-responsive properties to the hydrogel, thereby facilitating the sustained release of bioactive PA and its oligomers at the acidic microenvironment of the wound. Although native PA lacks photothermal activity, the HRP/H₂O₂-induced formation of dimeric and oligomeric PA structures endowed the hydrogel with intrinsic photothermal responsiveness, eliminating the need for additional photothermal agents. The PPA hydrogel exhibited excellent adhesion, hemostatic performance, photothermal conversion efficiency, antioxidant, antibacterial properties, and biocompatibility. When combined with photothermal therapy in a mouse infected wound model, the PPA hydrogel significantly accelerated wound closure, reduced local inflammation, promoted tissue regeneration and collagen deposition, highlighting its potential in skin wound repair.