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

Abstract

Compositional modification of bioactive 45S5 glass was performed by replacing the SiO 2 content partially or fully with B 2 O 3 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 B 2 O 3 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 μm) 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 SiO 2 -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 SiO 2 -rich core. The results are applicable to the development of bioaetive glasses with controllable conversion rates to HA, which may provide a novel class of scaffold materials for bone tissue engineering.