Structural features and antimicrobial activity of hydrogels obtained by the sol–gel method from silicon, zinc, and boron glycerolates

Glycerolates of biogenic elements, in particular, silicon, zinc, and boron, are promising biocompatible precursors in sol–gel processing. We successfully used them in the synthesis of pharmacologically active glycerohydrogels exhibiting wound healing, regenerating, and, in some cases, immunotropic and antimicrobial effects. In this paper, a comparative in vitro study of the antimicrobial (antibacterial and antimycotic) activity of four glycerohydrogels differing in biogenic elements (silicon-, silicon–boron-, silicon–zinc-, and silicon–zinc–boron-glycerol hydrogels) was carried out. Using the methods of agar diffusion and serial dilutions, it was shown that silicon–zinc–boron-glycerol hydrogel in general exhibited higher antimicrobial activity; silicon–boron- and silicon–zinc-glycerol hydrogels possessed lower activity; silicon-glycerol hydrogel demonstrated no antimicrobial properties. Differences in antimicrobial activity are associated with the structural features of hydrogels studied using advanced physicochemical methods, including electrospray ionization mass spectrometry, 11B NMR spectroscopy, and transmission electron microscope. It was found that a dispersion medium of silicon–zinc–boron-glycerol hydrogel, which was separated by exhaustive extraction with ethanol, contained bis(glycerol)borate anions [B(C3H6O3)2]–, along with Zn2+ cations. The simultaneous presence of these ions is not characteristic of other hydrogels under study and, in our opinion, provides improved antimicrobial activity of silicon–zinc–boron-glycerol hydrogel. Boron bisglycerolates and boric acid in a dispersion medium of silicon–boron-glycerol hydrogel provides its antimicrobial activity, whereas silicon–zinc-glycerol hydrogel containing only nanoscale particles of zinc monoglycerolate in cells of the 3D polymer network is less active. Silicon–zinc–boron-glycerol hydrogel can be an efficient and safer alternative to conventional topical antimicrobial agents for treatment of diseases of skin and mucous membrane.