A study of the formation of amorphous calcium phosphate and hydroxyapatite on melt quenched Bioglass^® using surface sensitive shallow angle X-ray diffraction

Abstract

Melt quenched silicate glasses containing calcium, phosphorous and alkali metals have the ability to promote bone regeneration and to fuse to living bone. These glasses, including 45S5 Bioglass^® [(CaO)_26.9(Na₂O)_24.4(SiO₂)_46.1(P₂O₅)_2.6], are routinely used as clinical implants. Consequently there have been numerous studies on the structure of these glasses using conventional diffraction techniques. These studies have provided important information on the atomic structure of Bioglass^® but are of course intrinsically limited in the sense that they probe the bulk material and cannot be as sensitive to thin layers of near-surface dissolution/growth. The present study therefore uses surface sensitive shallow angle X-ray diffraction to study the formation of amorphous calcium phosphate and hydroxyapatite on Bioglass^® samples, pre-reacted in simulated body fluid (SBF). Unreacted Bioglass^® is dominated by a broad amorphous feature around 2.2 Å⁻¹ which is characteristic of sodium calcium silicate glass. After reacting Bioglass^® in SBF a second broad amorphous feature evolves ~1.6 Å⁻¹ which is attributed to amorphous calcium phosphate. This feature is evident for samples after only 4 h reacting in SBF and by 8 h the amorphous feature becomes comparable in magnitude to the background signal of the bulk Bioglass^®. Bragg peaks characteristic of hydroxyapatite form after 1–3 days of reacting in SBF.