The Effect of Dissolution Medium on the Bioactivity and Phases Formed of Bioactive Glasses

Objectives: The chemical bond of bioactive glasses with the surrounding bone tissues depends on the transformation of the glass surface to an apatite like phase therefore; this material is widely used as coatings for implants. Glass bioactivity can be affected by the physiological solutions in which the glass is immersed. The aim of this study is to investigate the effect of proteins from cell culture media on the dissolution rate of bioactive glasses and their ability to form apatite.
Methods: Three glasses in the system of (SiO₂-CaO-Na₂O-P₂O₅-CaF₂) were prepared by a melt quench route, where the sodium content was varied. Each glass powder with particle size less than 38µm was immersed in 10% serum containing cell culture media and protein free cell media at 37^οC for 3, 7, 14, 21 and 28 days. The apatite formation on the surface of the glass powders was investigated by Secondary Electron Microscopy (SEM) and the crystalline phases were examined by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and ¹⁹F Nuclear Magnetic Resonance (NMR).
Results: All glasses dissolved slowly in both cell culture media and an apatite-like phase started to form after 21 days of immersion in the protein free media. While, the formation of apatite in the serum containing media did not occur during the course of the study. ¹⁹F NMR showed that the glasses when immersed in the serum free solution will form a carbonated fluorapatite where CO₃^2- and F^- ions replace PO₄^3- ion in the apatite crystal.
Conclusions: This study shows that the presence of proteins in culture media slows the rate of glass dissolution and decreases their ability to form apatite. However, the presence of high bicarbonate content in the culture media in the absence of proteins resulted in a new type of fluorocarbonated apatite being formed.