RESUMO
Sodium-calcium-phosphate based oxynitride glasses and glass-ceramics doped with Mg, Si, and Nb were studied in vitro in simulated body fluid (SBF) under static conditions. The release of ions and pH changes up to 7 days of immersion were investigated. The nitrogen incorporation into phosphate glass matrix was found to notably influence in vitro dissolution only of homogenous glasses. Increasing the nitrogen content in the samples decreased the mean mass loss, while the niobate incorporation increased it. The correlation between the nitrogen content and increase in pH of SBF was also observed. The presence of phosphates crystallites was found to support the dissolution process at the beginning step (up to 3 days).
RESUMO
Bioactive glasses have recently been extensively used to replace, regenerate, and repair hard tissues in the human body because of their ability to bond with living tissue. In this work, the effects of replacing Na2O with MgO on the electrical, biosolubility, and thermal properties of the target glass 10Na2O-60P2O5-30CaO (in mol%) were investigated. The electrical properties of the glasses were studied with the impedance spectroscopy technique. At 473 K, DC conductivity values decreased from 4.21 × 10-11 to 4.21 × 10-12 S cm-1 after complete substitution of MgO for Na2O. All samples had a similar activation energy of the DC conduction process ~1.27 eV. Conduction mechanisms were found to be due to hop of ions: Na+, Mg2+, and probable H+. FTIR analysis showed that, as the Mg content increased, the Q2 unit (PO2-) shifted towards higher wavenumbers. The proportion of Q3 unit (P2O5) decreased in the glass structure. This confirmed that the replacement of Na+ by Mg2+ was accompanied by concurrent polymerization of the calcium-phosphate glass network. The biosolubility test in the phosphate-buffered saline solution showed that the magnesium addition enhanced the biosolubility properties of Na2O-CaO-P2O5 glasses by increasing their dissolution rate and supporting forming CaP-rich layers on the surface. The glass transition temperature increased, and thermal stability decreased substantially upon substitution of Na2O by MgO.