Development of humidity and pH responsive ligand brush porous nanocapsules for self-controlled antibacterial properties without cytotoxicity

Abstract Specific pH and humidity response ligand brush porous nanocapsules (PNCs) were prepared by Pickering and colloidal methods. Ligand brushes capable of humidity and pH response were grafted onto the surface of PNCs to prevent the release of the core material through the pores. The mean diameters of the PNCs increased from 414.8 ± 105.6 nm to 527.8 ± 90.5 nm after grafting, and the sizes of the PNCs increased by 113 nm due to the grafted ligand brushes. Furthermore, using MAA polymer, which can have negative charges on the ligand brush on the surface at pH 5 or higher, the charge of the nanocapsule surface was -39.09 [mV] at pH 6 and 7. We carried out antibacterial experiments using Escherichia coli. The clear zones formed in the medium were 12-13 mm and were formed only at pH 6 and pH 7. Furthermore, in experiments at pH 4, 6, and 7 with 100% RH, the proliferation of E. coli was the slowest at pH 6. PNCs displayed antibacterial activity and inhibited proliferation of E. coli in an environment where humidity and pH conditions were satisfied and no cytotoxicity was observed with epithelial A549 cells.