Microengineered Membranes for Sustainable Production of Hydrophobic Deep Eutectic Solvent-Based Nanoemulsions by Membrane Emulsification for Enhanced Antimicrobial Activity

Abstract

This work tackles the quest for temperature-responsive greener solvents by synthesizing a hydrophobic deep eutectic solvent (DES) comprising menthol and decanoic acid. The low solubility of hydrophobic solvents in polar media was addressed by dispersing DES as oil-in-water nanoemulsions allowing their use in biomedical applications. DES-in-water nanoemulsions produced by ultrasound and membrane emulsification techniques were systematically compared. Microengineered isoporous membranes having 9 μm pore size were fabricated by laser machining. A membrane pitch of 100 μm was optimized to produce nanoemulsions 58.7 ± 0.4 nm in size at a dispersed phase flow rate of 0.02 mL min–1 leading to a new approach termed as membrane-assisted nanoemulsification. Subsequently, the optimized DES-based nanoemulsions subjected to antimicrobial susceptibility testing assays were 32 times more active against the Gram-positive bacteria, S. aureus ATCC 6538, than against the Gram-negative bacteria, E. coli ATCC 8739. In contrast to the non-emulsified DES or its individual components, 16 times less chemicals were required to inhibit bacterial activity when tested as nanoemulsions, suggesting increased bioavailability and a synergistic effect of all components in nanoemulsions potentiating their antibacterial activity. Lastly, membrane-assisted nanoemulsification offers sustainable production of nanoemulsions with a better control over size and dispersity along with lowered energy consumption when compared to ultrasound emulsification.