SBF Immersion Time Effects on Sol-Gel Phosphate Glass-Ceramic Structure

Abstract

Aqueous sodium metasilicate (Na₂SiO₃.5H₂O) was employed in present work as a precursor to synthesize silica for the preparation of a bioactive glass-ceramic with a SiO₂-CaO-Na₂O-P₂O₅ composition via the sol-gel method. Following sintering at 900°C for one hour, X-ray diffraction (XRD) analysis identified the primary crystalline phase as sodium calcium silicate (Na₂Ca₂Si₂O₉), accompanied by a secondary phosphate phase with a hexagonal structure. In vitro bioactivity was evaluated using simulated body fluid (SBF), revealing the formation of polycrystalline hydroxyapatite (Ca₁₀(PO₄)6(OH)₂) on the sample surface. During a 7-day incubation in SBF, the robust crystalline Na₂Ca₂Si₃O₉ phase transformed into an amorphous structure, indicating to biodegradation process. Results of atomic force microscopy (AFM) showed that the average grain size increased with extended SBF immersion time, the images of scanning electron microscopy (SEM) revealed flake-like structures corresponding to the Na₂Ca₂Si₃O₉ phase and filamentous formations indicative of apatite. After immersion, the sample surface became coated with a hydroxyapatite layer similar to that found in human bone. Elemental analysis confirmed the glass-ceramic composition and indicated an increase in phosphorus and calcium content post-immersion, alongside the appearance of new peaks corresponding to magnesium, potassium, and chlorine, while some sodium ions were released into the solution. Fourier-transform infrared (FTIR) spectroscopy identified characteristic bands of crystalline silicates and phosphates, whereas intensity of the P–O vibrational bands increased, while the Si–O–Si stretching bands decreased after SBF immersion, consistent with hydroxyapatite layer formation. The resulting monolithic material shows strong potential for use as a scaffold in tissue engineering applications.