Synthesis of Sr-Containing Mesoporous Bioactive Glasses

Mesoporous bioactive glasses containing 4% molar percentage of strontium (Sr/Ca/Si = 4/11/85) were synthetized exploiting a base-catalyzed sol–gel method following the protocol previously reported by the authors [13 (link)]. Briefly, Sr-containing nanosized MBG (MBG_Sr4%) were produced dissolving 6.6 g of cetyltrimethylammonium bromide (CTAB, ≥98%, Sigma Aldrich, Milan, Italy) and 12 mL NH₄OH (ammonium hydroxide solution, Sigma Aldrich, Milan, Italy) in 600 mL of ddH₂O. Thirty mL of tetraethyl orthosilicate (TEOS, Tetraethyl orthosilicate, Sigma Aldrich, Milan, Italy), 4.13 g of calcium nitrate tetrahydrate (Ca(NO₃)₂·4H₂O, 99%, Sigma Aldrich, Milan, Italy) and 1.68 g of strontium chloride hexahydrate (SrCl₂·6H₂O, for analysis EMSURE^® ACS) were subsequently added and the resulting suspension was kept under vigorous stirring for 3 h. After centrifugation (Hermle Labortechnik Z326, Hermle LaborTechnik GmbH, Wehingen, Germany) at 10,000 rpm for 5 min, the final precipitate was washed once with distilled water and two times with absolute ethanol, and finally dried at 70 °C for 12 h. The powders were further calcined at 600 °C in a furnace (Carbolite 1300 CWF 15/5 Carbolite Ltd., Parson Lane, Hope, Hope Valley, UK) to avoid CTAB residues.