Investigating the Structure, Solubility and Bioactivity of Na/Sr Bioactive Glasses/Glass-Ceramics
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This project was to investigate the structure, solubility and bioactivity of Na/Sr Bioactive glasses. There are three sections to this study. The first section is the effect of Na+ and Sr2+ on the structure and biocompatibility of the glasses. Three glasses (Ly-N, Ly-C, Ly-S) were formulated with the substitution of sodium (Na+) and strontium (Sr2+) within the glass. X-ray diffraction (XRD), X-ray Fluorescence (XRF), Differential Thermal Analysis (DTA), Hot Stage Microscope (HSM) were used to characterize the series of glasses. Results of Network Connectivity (NC), Xray Photoelectron Spectroscopy (XPS), Raman Spectroscopy, Magic Angle Spinning – Nuclear Magnetic Resonance (MAS-NMR) presented that the three glasses have very similar structure and Na+ and Sr2+ both act as network modifiers. Cell Culture testing was conducted to investigate the biocompatibility and bioactivity of these glasses. The series of glasses have no negative influence on the cell viability, and addition of Sr2+ increase the cell viability. The second section investigates the mechanical durability of the bioactive glasses as a function of structure, solubility and incubation time. Samples were sintered to amorphous and crystalline structures. Ion release profiles were determined over 1, 7 and 30 days and in each case ion release was greatly reduced when the materials were crystallized. pH changes were reduced with the onset of crystallization compared to the amorphous counterparts. The highest concentrations of Na+ (216 μg/mL) and Si4+ (172 μg/mL) both coming from Ly-N with amorphous structure. Crystalline samples presented much higher hardness values which did not reduce with respect to incubation time. However, the hardness of amorphous samples was found to experience significant reduction. The third part is simulated body fluid (SBF) testing and cytocompatibility of the glasses. In this section, sintered glass powder discs (amorphous /crystalline) were used to do SBF trials. Each material was subjected to maturation in SBF after 1, 7 and 30 days to describe any change in surface morphology. Scanning Electron microscopy (SEM) was used to observe the calcium phosphate (CaP) layers formed on the surface of each material. CaP deposition was observed predominantly on Na+-containing amorphous and crystalline materials. Limited CaP deposition was observed on the surface of Sr2+-containing crystalline materials. Cell culture analysis presented an increase in cell viability with Na+-containing materials and a general reduction in cell viability with Sr2+- containing material, however these reduction were not significant.