Aqueous-phase synthesis of cationic hydrogel nanoparticles with antibacterial properties

Antibacterial hydrogel nanoparticles are expected to be used in many biomedical applications, such as drug delivery and the development of antibacterial materials. In this study, we developed a synthesis for hydrogel nanoparticles that are dispersible in liquid media and have antibacterial properties. The particles were synthesized by copolymerizing a hydrophilic monomer (2-hydroxyethyl methacrylate), a cationic monomer containing a quaternary ammonium cation (trimethylaminoethyl methacrylate chloride), and a crosslinker (ethylene glycol dimethacrylate) in an aqueous solution with a cationic polymerization initiator (2,2 '-azobis[2-(2-imidazolin-2-yl) propane] dihydrochloride) to form a hydrogel. A hydrophobic monomer (methyl methacrylate) was then added and the polymerization was continued. The number average particle diameter by scanning electron microscopy was 122 nm, and the hydrodynamic diameter by dynamic light scattering measurement in water was about 380 nm, suggesting swelling of the particles by water. Furthermore, water was able to penetrate the solidified dry powder, confirming the hydrophilic properties of the particles. The zeta potential of the particles was about +40 mV, and bovine serum albumin, which generally has a high adsorption to positively charged substances, was adsorbed in large amounts to the particle surface, indicating that the particles had sufficient cationicity. The particles maintained stable dispersions even in liquid media with high ionic strength and containing impurities, which is important for nanoparticles used in medical and hygiene applications. The antibacterial activity of the particles was evaluated by incubation with Klebsiella pneumoniae, a Gram-negative bacterium. Almost no K. pneumoniae remained present in the supernatant after incubation, demonstrating the antibacterial properties of the particles.