Antimicrobial Composite Nanofiber Membranes Containing Cross-Linked β-Cyclodextrin Encapsulated Essential Oils

Abstract Membrane biofouling leads to low permeate quality and increased operational costs due to the need for frequent physical and chemical cleaning. Incorporation of antimicrobial agents such as essential oils (EOs) into polymeric membranes presents a promising solution to mitigate membrane biofouling. In this work, a cross-linked β-cyclodextrin (βCD) polymer, a biodegradable compound, was used to encapsulate seven commercial EOs, including thyme, peppermint, manuka, clary sage, tea tree, kanuka, and basil oils that were then incorporated into nanofibers that were deposited on an ultrafiltration membrane. Among these EOs, thyme oil exhibited the strongest antimicrobial activity against both Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli), while peppermint, manuka, and clary sage oils significantly inhibited S. aureus growth. In entrapment efficiency experiments, both βCD and cross-linked βCD polymer (βCDP) demonstrated comparable entrapment efficiency, ranging from 20 to 90%, with thyme, peppermint, clary sage, and kanuka oils achieving over 50%. Fourier-transform infrared spectroscopy and thermogravimetric analysis confirmed the successful encapsulation of EOs, and that their thermal stability was enhanced in EOs/βCDP inclusion complexes. Antibacterial activity assays using EOs/βCDP composite nanofiber membranes (CNMs) indicated that thyme oil exhibited superior inactivation efficacy against S. aureus by 13%, consistent with the results of the disk diffusion tests, while other EOs and control membranes showed no significant improvement. Both the polyethersulfone and all EOs/βCDP CNMs displayed a higher resistance to attachment by microorganisms, with the number of adhered S. aureus being at least ten times lower than that of the control membranes. The implementation of EO/βCDP CNMs offers advantages of low membrane resistance, high specific surface area and presents a sustainable antimicrobial strategy for water treatment applications.