Quaternary ammonium eutectogels as a printable, antimicrobial material platform†

Abstract

The solvent-free photopolymerization of a eutectic mixture consisting of a quaternary ammonium methacrylate salt, urea, and functional co-monomer to yield polymeric eutectogels with unique properties and function is reported. Herein, we prepare eutectic solvents based on urea as a hydrogen bond donor, [2-(methacryloyloxy)ethyl]trimethylammonium chloride (METAC) as a hydrogen bond acceptor, and 2-hydroxyethyl methacrylate (HEMA) as a comonomer to modulate physical properties, such as viscosity and hydrophilicity. METAC was used as the isolated salt, rather than as aqueous solution, to directly prepare water-free eutectic solvents with control over the final composition. These viscous, room-temperature stable liquids possess tunable glass transition temperatures and shear-dependent viscosity. Their direct photopolymerization, either via ultraviolet or visible-light-mediated methods and in the presence of crosslinker, gives rise to polyelectrolyte eutectogels with very high and tunable swelling capacity in aqueous media. The viscous nature of the eutectic mixture enables rapid photopolymerization kinetics compared to the equivalent process in water, with close to seven-fold increase in polymerization. Their cationic nature gives the gels inherent antimicrobial properties, as shown through their deactivation of S. aureus bacterial cells. Variation of the crosslinker concentration enables eutectic resins to be formed that show potential for direct ink writing (DIW) photopolymerization methods, highlighting the versatility of these materials.