Characterization of silicon nitride powders and assessment of antibacterial properties: the effect of pH

Abstract

Progress in the development and understanding of antibacterial materials could contribute in limiting the spreading of drug-resistant bacteria and lowering the number of infections. Silicon nitride (Si3N4) has great properties for biomedical applications and recent studies reported on its ability to hinder bacterial adhesion and chemically affect microbial viability. Here Si3N4 powders were tested aiming at further understanding of the mechanism and its dependency on pH. Experiments were performed in liquid cultures of S. epidermidis (0-24h) and P. gingivalis (0-72h) using 4 and 16 mg of powder per mL of culture broth. Five initial pH values were used: 5.5, 6.5, 7.5, 8 and 8.5. The mere powders were exposed to the same pH conditions and characterized afterwards by vibrational spectroscopies, XPS and zeta potential measurements. The antibacterial effects were assessed using WST-8 assay and Raman spectroscopy. The powder concentration of 16 mg/mL had a stronger impact, according to both WST and spectroscopic data. Silicon nitride activity was appreciable in both acidic and basic conditions but varied with pH and bacterial strain, as supported by variations in relevant Raman bands. The characterization of the powders revealed oxidation, to a variable extent depending on the pH treatment. It is confirmed that the antibacterial activity of Si3N4 depends on pH and is related to surface chemistry and dissolution phenomena. Further research could elucidate the involved reactions.