Bioactivity of microporous borate glass-ceramics prepared from solution and derived glasses

Microporous borate compositions based on the formula xB2O3•(100–x)(0.5CaO•0.45Na2O•0.05P2O5) (x = 56.1 and 51.1 mol%) have been prepared from solution. The dried products were subjected to heat-treatment at 600 and 700 °C for 3 h to obtain borate glass-ceramics with scaffold-like structure. Bioactivity and degradation were tested in simulated body fluid (SBF) at 37 °C for different time intervals. Scanning (SEM) and transmission (TEM) electron microscopy, infrared spectroscopy (FTIR) and X-ray diffraction (XRD) were used to examine the correlation between bioactivity and microstructure. Results indicated that the type and concentration of crystalline CaNaB5O9 and CaNa3B5O10 phases, in addition to concentration of bridging and non-bridging oxygen atoms, are the factors affecting the apatite forming ability and composition degradation. XRD and SEM results showed that the as-prepared compositions and those heat-treated at 600 and 700 °C are crystalline matrices, while TEM-EDP of selected region exhibited halo diffuse intensity with clear bright spots. These features indicate that the crystalline phases are dispersed in amorphous phase. After immersion in SBF, TEM-EDP proved that the crystalline hydroxyapatite (HA) phase was formed on amorphous phase. The type of product after reaction in SBF is influenced by the nature of borate network. For melt-derived borate glasses, hydrous species of B(OH)3 and amorphous calcium phosphate are formed. Microporous borate glass-ceramics exhibited a good in vitro bioactive response through the formation of hydroxyapatite, except when the matrix is rich in CaNa3B5O10 phase. The results of this study suggest that the solution-method can be used to prepare microporous bioactive borate glass-ceramics, such as three-dimensional porous scaffolds, which are of particular interest for the clinical application in bone regeneration.