Antibacterial effect and cell metabolic activity of Na2CaSi2O6, β-NaCaPO4, and β-NaCaPO4-SiO2 versus hydroxyapatite

Hydroxyapatite (Ca5(PO2)3(OH)) is extensively used in diverse clinical applications because of its relatively simple synthesis protocol, low cost, and chemical similarity to the mineral component of bones and teeth. Some limitations regarding bioactivity and antibacterial activity have motivated changes in its structure and the development of alternative materials to achieve better performances as bioceramics. In this study, the antibacterial effect and cell metabolic activity of the main crystalline phases (Na2CaSi2O6, β-NaCaPO4, and β-NaCaPO4−SiO2) derived from the original 45S5 bioactive glass were evaluated and compared with those induced by a commercial powder of hydroxyapatite. Powder samples of Na2CaSi2O6, β-NaCaPO4, and β-NaCaPO4−SiO2 were synthesized by a simple and reproducible solid-state reaction method. The β-NaCaPO4−SiO2 sample exhibited the strongest effect against Pseudomonas aeruginosa, Staphylococcus aureus, and S. epidermidis, which are bacteria that normally colonize the skin but can become opportunistic pathogens when the host's resistance is low. All bacteria were eliminated within 5 min in the direct-contact test, an effect that is likely associated with changes in pH in the microenvironment generated from the partial solubilization of the material and the action of certain released ions, such as Ca2+. In vitro experiments with human cells, no sample showed cytotoxicity, and the β-NaCaPO4−SiO2 sample stood out once more inducing the most positive effect on keratinocyte and stem cell viability. Overall, the tested materials demonstrated similar or better (β-NaCaPO4−SiO2) biochemical properties than hydroxyapatite. This finding encourages us, and perhaps other research groups, to assess the bio-performance of these materials more comprehensively, aiming at the development of new products for use in tissue engineering.