Synergistic bactericidal and anticancer potential of rubidium and silver-containing phosphate-based bioglasses

A new vitreous system, 44P₂O₅·25CaO·21Na₂O·5ZnO·5Ag₂O, doped with 1-7 mol% Rb₂O, was synthesized by conventional melt quenching, and the structural and biological effects of rubidium incorporation were systematically investigated. The X-ray diffraction confirmed the amorphous nature of all compositions, while FTIR and Raman spectroscopy revealed that Rb⁺ ions act as network modifiers, promoting progressive depolymerization of the phosphate network dominated by Q² and Q¹ units. X-ray photoelectron spectroscopy demonstrated the presence of all constituent elements at the glass surface, with silver detected in both ionic (Ag⁺) and metallic (Ag⁰) states; the Ag⁺/Ag⁰ ratio varied slightly (0.62-0.65) with Rb₂O addition, indicating stable coexistence of ionic species and metallic nanoparticle clusters. Transmission electron microscopy corroborated the formation of Ag-containing nanoclusters dispersed within the vitreous matrix. Biological performance was evaluated through a comprehensive series of assays, including fibroblast viability (MTT), antimicrobial, antifungal, and anticancer tests. Human skin fibroblasts displayed a high proliferation rate at both 24 and 48 h, confirming the excellent cytocompatibility of the glass system in the 0-5 mol% Rb₂O compositional range. In contrast, a pronounced cytotoxic effect was recorded against breast cancer cells for the composition containing 7 mol% Rb₂O at a concentration of 0.78 mg mL^-1 after 48 h. Antimicrobial testing revealed complete elimination of gram-negative bacteria within 1 h, attributed primarily to Ag⁺ release. A bacteriostatic effect against gram-positive strains at 2 h, as well as inhibition of fungal propagation at 4 h, was also observed and correlated with the surface concentration of silver and rubidium.