(626j) Surface Characteristics of Polymer Nanoparticles and Its Application to Antibacterial Materials

Bacterial infection has been a major issue in human health, and various antibacterial substances have been developed until now. Antibacterial materials, which physically kill bacteria by membrane damage with contact to them, have been developed. Due to this mechanism, antibacterial materials are effective toward drug resistance bacteria. Various kinds of antibacterial materials have been reported: inorganic particles (e.g., TiO₂), organic particles (e.g., cationic polymer particles), and natural substance-based materials (e.g., chitosan derivatives). Especially, cationic polymer is a promising antibacterial material because of the adsorption on bacteria by electrostatic interaction and contribution of hydrophobic polymer backbone to membrane damage.

In our previous work, polystyrene (PSt) particles were synthesized with a cationic initiator of 2,2’-azobis-[2-(1,3-dimethyl-4,5-dihydro-1H-imidazol-3-ium-2-yl)] propane triflate (ADIP), whose strongly cationized group makes the PSt particles broadly applicable as pH-independent antibacterial materials. The cationic PSt particles exhibit antibacterial activity to Staphylococcus epidermidis [Ref1]. In this study, the surface characteristics of the cationic PSt particles were investigated, which contribute to developing powerful antibacterial materials. A fluorescent probe, 6-dodecanoyl-2-dimethylaminonaphthalene (Laurdan) was used to evaluate the hydrophobicity surrounding the particle surfaces. Laurdan emits its fluorescence depending on the polarity around itself, which enables to evaluate the surface polarity of the particles dispersing in aqueous solution. Because the surface hydrophobicity of particles is reflected by the local polarity of particle surfaces, fluorescent spectra of Laurdan in suspensions of the particles were measured. The surface polarity of the PSt particles synthesized with ADIP and (vinylbenzyl)trimethylammonium chloride (VBTMAC) is low compared to that of conventional PSt particles [Ref2]. The antibacterial activity of the particles was evaluated by minimum inhibitory concentration (MIC) against S. epidermidis. As a result, lower polarity surface of the PSt particles synthesized with ADIP tends to exhibit stronger antibacterial activity. Both cationic property and hydrophobicity should be, consequently, considered to develop strong antibacterial materials.

[Ref 1] K. Suga et al., ACS Appl. Bio Mater., 5, 2202−2211 (2022)

[Ref 2] A. Nagasawa et al., Colloids Surf. A, 656, 130376 (2023)