Abstract:

Objective The effective management of wound exudate, provision of sustained antibacterial and anti-inflammatory effects, and maintenance of lightweight breathability and moisture balance remain critical challenges in the development of advanced wound dressings. Existing multifunctional dressings often suffer from limitations such as inefficient unidirectional moisture transport, inadequate antibacterial durability, or complex preparation processes. This study aims to fabricate a Janus-structured nanofiber membrane that integrates superior unidirectional moisture-wicking capability, broad-spectrum antibacterial activity, and high antioxidant performance, addressing the aforementioned drawbacks for potential applications in wound care.

Method The PPT-PZ Janus membrane was fabricated via two-step electrospinning. First, a hydrophilic PAN/PVP/THY (PPT) layer was prepared from a DMF solution (1.2 g PAN, 0.5 g PVP, 1.0 g THY) at 20 kV, 20 cm distance, 0.003 5 mm/s feeding rate, 100 r/min drum speed, for 2 h. Then, a hydrophobic PLA/ZnO (PZ) layer was electrospun onto PPT from an HFIP solution (1.4 g PLA, 0.3 g ZnO) at 16 kV for 25 min (other parameters matched PPT). Single-layer PPT and PZ membranes served as controls. Evaluations included SEM, FTIR, contact angle, water absorption, DPPH, and antibacterial tests against E. coli (ATCC 25922) and S. aureus (ATCC 6538).

Results SEM observations revealed distinct morphological differences between the two layers of the PPT-PZ membrane. The hydrophilic PPT layer exhibited finer fibers with an average diameter of 0.62 μm, while the hydrophobic PZ layer showed coarser fibers with an average diameter of 1.29 μm, forming a gradient pore structure across the membrane thickness that enhances directional liquid transport. Cross-sectional images confirmed a clear layered interface between the PPT and PZ layers, ensuring structural integrity without interlayer detachment. FTIR analysis verified the successful incorporation of THY (a natural antioxidant with phenolic groups) into the PPT layer (via characteristic peaks at 806 cm^-1 and 2 959 cm^-1, corresponding to benzene ring vibrations and alkyl chain stretches) and the effective combination of ZnO with PLA in the PZ layer (via attenuated peaks at 1 750 cm^-1 and 1 181 cm^-1, indicating interactions between PLA's ester groups and ZnO nanoparticles). Dynamic contact angle tests demonstrated excellent unidirectional moisture transport: when the hydrophilic layer faced upward, water droplets were completely absorbed within 8 s. When the hydrophobic layer faced upward, initial hydrophobic behavior (similar to the single-layer PZ membrane) transitioned to full absorption within 8 s, confirming controlled directional water movement. The PPT-PZ membrane achieved a high water absorption rate of 2 776% and an equilibrium water content of 95%, indicating its ability to manage large volumes of wound exudate effectively while maintaining a moist microenvironment conducive to healing. Antioxidant tests showed that the PPT-PZ membrane exhibited a DPPH radical scavenging rate of 86.5%, significantly higher than that of the single-layer PZ membrane (40.0%), attributed to the synergistic effect between THY and ZnO nanoparticles (which enhance radical capture via surface defects). Antibacterial assays demonstrated that the PPT-PZ membrane exerted a 99.99% inhibition rate against both E. coli and S. aureus, outperforming the single-layer PPT (99.99% against S. aureus and 100% against E. coli) and PZ (99.77% against E. coli) membranes. This enhanced antibacterial activity was attributed to the "membrane damage-ion penetration-oxidative stress" mechanism, where THY disrupted bacterial cell membranes, facilitating ZnO-derived Znion penetration and reactive oxygen species (ROS) generation to induce oxidative stress, collectively inhibiting bacterial growth.

Conclusion The Janus-structured PPT-PZ nanofiber membrane, fabricated via a simple two-step electrospinning process, successfully integrated multiple key functions required for advanced wound dressings. Its gradient fiber structure enabled efficient unidirectional moisture transport, preventing exudate reflux while maintaining wound moistness. The synergistic interaction between THY and ZnO endowed the membrane with both high antioxidant activity (86.5% DPPH scavenging) and broad-spectrum antibacterial efficacy (99.99% inhibition against common pathogens). These properties, combined with its favorable breathability (26.70 mm/s) and simple preparation process, made it a promising candidate for multifunctional wound care applications, addressing critical limitations of existing dressings.

Key words: functional fiber, medical dressing, electrospinning, asymmetric structural nanofiber membrane, antioxidation property, synergistic antibacterial, unidirectional moisture transport