Solubility of 15MgO-15CaO-5P₂O₅-10SiO₂ glass

Mg2+ and silicate ions are important ionic species in bone formation. Previously, the authors' group reported a 15MgO-15CaO-8P(2)O(5)-4SiO(2) glass (silicophosphate invert glass [spIG]) containing orthophosphate and orthosilicate structures. Mg2+ and Ca2+ ions in the glass preferentially formed Si-O-Mg and P-O-Ca bonds, respectively, suppressing the release amount of silicate ions in a tris-HCl buffer solution (TBS). In this study, a new 15MgO-15CaO-5P(2)O(5)- 10SiO(2) invert glass without a silicate 3D-network structure was prepared via a melt-quenching method. The new glass exhibits an improved silicate-ion release ability that promotes bone formation. The dissolution amounts of Ca2+ and phosphate ions from the glass into a TBS were similar to those of spIG, but the amounts of Mg2+ and silicate ions increased by similar to 2 and similar to 5 times, respectively. P-31 and Si-29 magic-angle spinning nuclear magnetic resonance spectroscopic analyses showed that the glass was composed of orthophosphate and chain silicate structures. Even when the silica content exceeded that of spIG, the formation of a silicate 3D-network was suppressed. The O1s X-ray photoelectron spectra indicated that (Si, P)-O-Mg bonds contribute to the glass formation. In a glass model based on classical molecular dynamics, the oxygen coordination numbers of Mg and Ca were determined as 4-7 and 5-8, respectively. Mg2+ ions are predominantly responsible for bridging the silicate/phosphate structures in this glass and play an important role in tuning the glass formation and the release amount of silicate ions.