The silver influence on the structure and antibacterial properties of the bioactive 10B2O3− 30Na2O−60P2O2 glass

The calcium-free bioactive borophosphate glasses were doped with Ag2O in order to improve their properties with antibacterial activity. The samples belonging to the system (100 − x)[10B2O3·30Na2O·60P2O5]xAg2O, with 0 ≤ x ≤ 2, were obtained by melt-derived technique and characterized by X-ray diffraction, UV-vis spectroscopy, transmission electron microscopy and Raman spectroscopy and afterwards their aseptic character was assessed. The Listeria monocytogenes were used to test the antibacterial effect of the undoped and silver-doped glasses. Important structural changes induced by the Ag2O addition to the bioactive glass composition have been identified especially for the samples containing a small amount of silver oxide (x = 0.1) and for the highest Ag2O content (x = 2). By varying the silver amount the presence of different silver species was observed, i.e. Ag+, Ag0, isolated Ag nanoparticles and aggregated Ag nanoparticles. The Ag+ and Ag0 species were present in all silver containing samples, while the existence of isolated Ag nanoparticles was observed only for x = 1, 1.5 and 2 mol% Ag2O. It was found that the glasses containing silver-oxide content between 0.2 and 1 mol% exhibit a relatively increased antibacterial activity, while the samples with 1.5 and 2 mol% Ag2O were found to exhibit a reduced antibacterial effect against L. monocytogenes. This behavior can be associated with the appearance of the small silver nanoparticle clusters in the glass system.