Mechanisms for Converting Bioactive Silicate, Borate, and Borosilicate Glasses to Hydroxyapatite in Dilute Phosphate Solution


The mechanisms by which a bioactive silicate glass (designated 45S5), a borate glass, and two intermediate borosilicate glass compositions convert to hydroxyapatite (HA) in dilute phosphate solutions were investigated. The borate and borosilicate glasses were derived from the silicate glass by fully or partially replacing the SiO2 with B2O3. Kinetic, chemical and microstructural changes accompanying the conversion of the glasses to HA were comprehensively characterized. Increasing the B2O3 content of the glass produced an increase in the conversion rate and a decrease in the pH of the solution. The conversion started at the surface of the glass and moved inward. For particles with a size of 150-300 μm, conversion of the borate glass went to completion within 3 days, yielding pseudomorphic HA particles with a nanoscale structure, but the silicate and borosilicate glasses were only partially converted even after 75 days, giving a composite structure consisting of a SiO2-rich core surrounded by a HA layer. Regardless of the composition, all the Na2O and B2O3 present in the glass particles dissolved into solution, but the CaO either reacted to form HA or remained in the unconverted SiO2-rich core. A qualitative model is developed to describe the conversion of the glasses to HA.


Materials Science and Engineering

Keywords and Phrases

Bioactive Silicate Glass; Borate Glass; Borosilicate Glass; Dilute Phosphate Solutions; Hydroxyapatite

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Document Type

Article - Journal

Document Version


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© 2006 Society of Glass Technology, All rights reserved.

Publication Date

01 Jan 2006