Physicochemical properties of bacterial cellulose/phototherapeutic polypyrrole/antibacterial chitosan composite membranes and their evaluation as chronic wound dressings

Bacterial cellulose (BC) is a natural fiber membrane and has been applied in many biomedical applications. Herein, it was used as the main scaffold to prepare wound dressings for treating diabetic skin wounds. Polypyrrole (PPy) was first synthesized by in situ oxidative polymerization within BC membrane and applied as a photothermal agent, followed by coating with chitosan (CS) to improve the biocompatibility and antibacterial properties. SEM pictures revealed sub-micron PPy particles ranging from 100 to 200 nm were formed and attached to the BC fibrils, whereas CS formed a thin, porous layer on the surface. FTIR analysis showed that there was hydrogen bonding between BC, PPy and CS components. The crystalline structure of BC was maintained yet with decreased crystallinity by addition of PPy and CS. The water absorption capability and water vapor transmission rate decreased by PPy incorporation owing to its hydrophobic nature, but they were regained by addition of hydrophilic CS. The prepared BC/PPy/CS membrane was biocompatible toward L929 cells and maintained hemocompatibility. Additionally, both PPy and CS contributed to the antibacterial activity against Staphylococcus aureus, Pseudomonas aeruginosa, and Escherichia coli, while they demonstrated a potential for synergistic antibacterial effects when combined. Finally, the near-infrared (NIR)-driven photothermal-hyperthermic effects by PPy on lesions upregulated heat-shock protein (HSP) expression and anti-inflammatory properties by CS boosted restoration of diabetic wounds in vivo without the addition of any antibiotics or anti-inflammatory drugs. The results thus support using the BC/PPy/CS membrane for diabetic wound regeneration.