The behaviour of hydroxyapatite ceramics in an aqueous environment

Abstract

Hydroxyapatite ceramic prosthetic materials were exposed for 4 wk to a physiologic solution of known ionic composition as determined by inductively coupled plasma emission spectroscopy. The corrosion medium was kept at 70 ° C, changed each week for a fresh lot and the 7 d old medium re-analysed to establish the change in ionic content. Scanning electron microscopy was performed on the prosthetic materials to compare their surface ultrastructure before and after the corrosion test. SEM showed that the corrosion exposure seemed to have changed the surface of the ceramics through formation and deposition of spheritical precipitates with diameters up to 1.3μm. The spectral analysis seemed to lead to the deduction that the corrosion exposure had induced a change in surface composition from Ca∶P ratios suggestive of basic calcium phosphates (apatite, beta tricalcium phosphate (β-TCP)) to those perhaps implying equilibrium with monetite and brushite. Ignoring the effect of adsorption of other ions, it is argued that this shift could be attributed to the incorporation of H+ from the aqueous solution. It is speculated that these surface chemical and morphological changes might be playing a role in the physico-chemical genesis of the bond known to occur between implanted HA and bone tissue.