Structure and Stability of High CaO- and PO-Containing Silicate and Borosilicate Bioactive Glasses.

The present work elucidates about the structure of bioactive glasses having chemical compositions expressed as (mol %) (50.0 - )SiO-BO-9.3NaO-37CaO-3.7PO, where = 0.0, 12.5, 25, and 37.5, and establishes a correlation between the structure and thermal stability. The structural modifications in the parent boron-free glass (B0) with the gradual substitutions of BO for SiO are assessed by Raman and Si, P, B, and Na magic angle spinning (MAS)-nuclear magnetic resonance (NMR) spectroscopies. The structural studies reveal the presence of Q and Q structural units in both silicate and borosilicate glasses. However, Q(3B) units additionally form upon incorporating BO in B0 glass. B-containing silicate glasses exhibit both three-coordinated boron (B) and four-coordinated boron (B) units. The P MAS-NMR studies reveal that the majority of phosphate species exist as isolated orthophosphate (Q) units. The incorporation of BO in B0 glass increases the cross-linking between the SiO and BO structural units. However, incorporation of BO lowers the glass thermal stability (Δ), as shown by differential scanning calorimetry. Although both silicate and borosilicate glasses exhibit good in vitro apatite-forming ability and cell compatibility, the bactericidal action against bacteria is more evident in borosilicate glass in comparison to silicate base glass. The controlled release of (BO) ions from boron-modified bioactive glasses improves both the cell proliferation and the antibacterial properties, making them promising for hard tissue engineering applications.