Conversion of Bioactive Silicate (45S5), Borate, and Borosilicate Glasses to Hydroxyapatite in Dilute Phosphate Solution

Summary: Compositional modification of bioactive 45S5 glass was performed by replacing the SiO2 content partially or fully with B2O3 to form borosilicate and borate glasses. Its effect on the conversion of the glass to hydroxyapatite (HA) in dilute phosphate solution was investigated using kinetic, chemical, and structural techniques. A higher BzO3 content of the glass produced an increase in the conversion rate and a decrease in the pH of the solution. Particles of the borate glass (150-300 m) were fully converted within 4 days, yielding pseudomorphic HA particles with a nanoscale structure. Silicate and borosilicate. glass particles were only partially converted even after 70 days, forming a composite structure consisting of a SiO2--rich core surrounded by a HA layer. Regardless of the composition, all the Na and B present in the glass particles dissolved into solution, but the Ca either reacted to from HA or remained in the unconverted SiO2--rich core. The results are applicable to the development of bioactive glasses with controllable conversion rates to HA, which may provide a novel class of scaffold materials for bone tissue engineering