Abstract:

Objective Diabetic foot ulcers (DFUs) characteristically present a hyperglycaemic, alkaline, and highly exudative microenvironment that fosters recurrent infection and impedes healing. This work aims to construct a nanofiber composite dressing that couples antibiotic-free, glucose-triggered antibacterial activity with directional exudate management, thereby addressing both microbial control and moisture regulation at DFU wound beds within a single materials platform.

Method A bilayer architecture was designed comprising a hydrophobic polypropylene (PP) nonwoven substrate and a reconstructed hydrophilic top layer of short poly(vinylidene fluoride) (PVDF) fibers. Gold nanoparticles (Au NPs; glucose oxidase-like) and Fe-MIL-88NH₂ metal-organic framework (MOF; peroxidase-like) nanozymes were immobilized on PVDF via a tannic-acid-based adhesive (TBA). Short-fiber dispersions were prepared by high-shear homogenization and spray-reassembled onto PP to establish a wettability gradient. Catalytic performance was verified by methyl-red pH transition and 3,3',5,5'-tetramethylbenzidine (TMB) assays. Unidirectional wetting, mechanical behavior, antibacterial efficacy against Staphylococcus aureus (S.aureus) and Escherichia coli (E.coli), and cytocompatibility with human foreskin fibroblasts (HFFs) were systematically evaluated.

Results The nanozyme Fe-MIL-88NH₂ displayed a uniform octahedral morphology with an average particle size near 281 nm and reached maximal peroxidase-mimicking activity at approximately pH=4, while activity diminished under alkaline conditions. The PP substrate and reconstructed PVDF layer were assembled into a porous, interpenetrating network with clearly distinct fiber scales, measured as (15.68±0.26) μm for PP and (515±19.8) nm for PVDF. Methanol activation shifted PVDF toward a more polar state and reduced the static water contact angle from roughly (132.13°±1.63)° to (75.80±2.24)°, while the bilayer preserved a pronounced hydrophobic-hydrophilic asymmetry that is essential for moisture management. Ink-drop tracking confirmed stable unidirectional transport, where droplets placed on the hydrophobic PP face were drawn across the interface into the hydrophilic PVDF layer with an onset near 10 s, whereas droplets deposited on the hydrophilic face were rapidly absorbed and spread within about 5 s and did not seep backward over a 60 s observation window. Tensile testing showed that adding the reconstructed PVDF layer increased strength toward skin-like levels, with machine-direction strength around 11.4 MPa and cross-direction strength around 7.3 MPa, while elongation remained compliant for body motion at (53±8)% in the machine direction and (142±20)% in the cross direction. Cascade catalysis proceeded under physiologically relevant buffers. Au NPs oxidized glucose and lowered the local pH value over roughly 60 min, which activated Fe-MIL-88NH₂ to decompose in-situ-generated hydrogen peroxide and yield hydroxyl radicals (·OH), as indicated by the characteristic blue TMB product. This glucose-responsive cascade translated into potent broad-spectrum antibacterial performance in vitro, with inhibition rate against S.aureus and E.coli exceeding 97% by plate counting relative to controls. Cytocompatibility testing indicated minimal mammalian cell toxicity, with HFF viability maintained at or above 84% after 24 h of co-culture, supporting the safety of the immobilization strategy and matrix selection.

Conclusion The proposed dressing integrates a bilayer with a glucose-triggered Au-NP/Fe-MIL-88NH₂ nanozyme cascade, aligning exudate drainage and on-demand reactive oxygen species (ROS) generation within a single textile construct. The wettability gradient drives liquid unidirectionally from the hydrophobic interior to the hydrophilic exterior, preventing backflow and maintaining a drier wound interface, while the cascade efficiently suppresses bacteria under DFU-relevant glucose levels with ≥97% inhibition rate and preserves fibroblast viability (≥84%). Mechanically, the composite approximates skin-like strength and extensibility, supporting conformal coverage. The short-fiber reconstruction route achieves uniform, stable nanozyme anchoring throughout a porous hydrophilic layer, preserving catalytic accessibility and enhancing mass transfer. Collectively, these findings substantiate a materials strategy that couples exudate management with antibiotic-free antibacterial activity, offering translational promise for managing chronic, infection-prone DFUs. Future work may extend to in vivo validation under dynamic exudate flux, long-term stability of immobilized nanozymes, and optimization of layer thickness and fiber morphology for scalable manufacturing.

Key words: nanoenzyme, cascade antibacterial, unidirectional moisture transfer, nanofiber dressing, diabetic foot ulcers, polypropylene nonwoven, poly(vinylidene fluoride) fiber, medical textiles