Sofia Miguel Silva, Ana Afonso, Manuel Simões, Berta Nogueiro Estevinho
Bioactive wound dressings with antibacterial properties are attractive for infection control. Phytochemicals, products from plant secondary metabolism, like gallic acid (GA), ferulic acid (FA), coumaric acid (CouA) and perillyl alcohol (PA) show promising antimicrobial activity, but their poor water solubility and the high concentrations required for efficacy limit their application. To overcome this, Natural Deep Eutectic Solvents (NADES) provide a sustainable and biocompatible alternative to conventional solvents. NADES were used at sub-minimum bactericidal concentrations (MBC) to enhance phytochemical antimicrobial activity against Staphylococcus epidermidis and Escherichia coli. CC:Gly (100%) dissolved all tested phytochemicals. GA + CC:Gly:CA (20%) against S. epidermidis, and AP, CouA and FA with CC:Gly (100%) against E. coli, reduced the MBC from ≥4000 to 2000 μg/mL. The most promising phytochemical-NADES formulations were encapsulated into electrospun zein nanofibres to fabricate sustainable bioactive wound dressings. All electrospinning solutions exhibited Newtonian behaviour, and their viscosity and conductivity strongly influenced fibre morphology: CC:Gly formulations produced rough fibres with larger diameters (1253 ± 57 nm), whereas CC:Gly:CA yielded smooth fibres with smaller diameters (419 ± 45 nm). In vitro release studies demonstrated complete GA release within 50 min, following a non-Fickian diffusion. FTIR indicated encapsulation through physical entrapment. Among the antimicrobial assays performed, disk diffusion demonstrated the most evident activity, with Z + GA + CC:Gly:CA producing an inhibition zone of 18.7 mm, although further optimisation is required to improve performance in liquid-based assays. Overall, this study demonstrates the role of NADES as phytochemical solubilisers and antimicrobial enhancers, as well as functional components of electrospun sustainable wound dressing applications.