Comparison of the effects of magnesium additive on biological and mechanical properties of biogenic and commercial silica-based bioactive glasses

Abstract

This study investigates the in vitro bioactivity, biodegradability, and mechanical properties of Mg-doped (up to 6 wt.%) and undoped bioactive glasses synthesized using commercial silica and rice husk ash (RHA)-derived biogenic silica. In vitro bioactivity was assessed by immersing the glasses in simulated body fluid (SBF). The formation of a hydroxycarbonate apatite (HCA) layer on glass surfaces, a hallmark of bioactivity, was confirmed by scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy (FTIR). SEM images confirmed apatite formation on all samples, with the B2-R and B2-C glass samples (1.5 wt.% MgO) exhibiting the clearest surface mineralization and a well-developed apatite layer after 7 days of SBF immersion. FTIR spectra supported these findings, showing characteristic peaks of phosphate and carbonate groups, indicative of HCA. Biodegradability was assessed through weight loss measurements in SBF and Tris buffer, and ion release behavior was evaluated using inductively coupled plasma optical emission spectrometry (ICP-OES). Results showed that moderate Mg doping enhanced biodegradability and ion release in RHA-derived glasses, while excessive doping reduced it. Conversely, Mg doping had minimal impact on commercial silica-derived glasses. Tris buffer pH measurements and Vickers microhardness tests further supported the influence of Mg on ion exchange and structural compactness. Vickers hardness measurements showed a marked decrease for 1.5 wt.% Mg-doped glasses, with hardness values decreasing from 437 to 84 HV for B2-R and from 464 to 98 HV for B2-C after 28 days of SBF immersion. Notably, 1.5 wt.% Mg-doped glasses (B2-R and B2-C) demonstrated optimal bioactivity, evidenced by significant HCA formation, ion exchange, and hardness reduction after immersion. Overall, the findings emphasize that the silica source and Mg doping critically influence the some properties of bioactive glasses, with RHA-based glasses offering superior bioactivity and mechanical adaptability for bone regeneration applications.