An equilibrium study of phosphate precipitation on bioactive glass

A1 Journal article (refereed)


Internal Authors/Editors


Publication Details

List of Authors: Karlsson KH, Backman R, Hupa M
Publication year: 2002
Journal: Key Engineering Materials
Journal acronym: KEY ENG MAT
Volume number: 218-220
Start page: 103
End page: 108
Number of pages: 5
ISSN: 1013-9826


Abstract

The solubility of hydroxyapatite (HAP) depends on the concentration of calcium, phosphate and hydroxide ions. The paper discusses precipitation of HAP from a simulated body fluid (SBF). Thermodynamic calculations show that if equilibrium is attained, solid hydroxyapatite will precipitate from SBF. Metastable precursors, however, are reported to precede the apatite formation and equilibrium is attained only after several days. When in contact with a bioactive glass, alkali and alkaline earth ions are dissolved and a layer of hydrated silica is formed on the surface. In this gel pH drops from around 9.5 close to the glass to 7.2 close to the solution. The solubility of HAP decreases with increasing pH and as there further is an almost infinite number of nucleation sites in the hydrated gel, HAP precipitation starts earlier inside the gel than at its outer surface. It is suggested that the pH gradient and the heterogeneous nucleation sites explain the observed effect of silicate ions on HAP formation. Parallels are also drawn to formation of stem cells in blood vesicles.


Keywords

bioactivity of glass, bone, hydroxy(I)apatite, mineralisation, solubility product

Last updated on 2019-13-12 at 03:40