INHIBITION OF DISSOLUTION OF HYDROXYAPATITE POWDER BY ADSORBED ANIONIC POLYMERS

The effect of the presence in solution of neutral or anionic hydrosolu ble polymers on the kinetics of dissolution of hydroxyapatite powder ( HAP) is analysed at a constant pH of 5 and under well-controlled condi tions. Four polymers are studied. It is shown that the polymers that a re able to be adsorbed induce a decrease in the rate of dissolution wh ich strongly depends on the chemical structure of the polymers. Chemic al groups with the ability to bind calcium ions, such as phosphate and phosphonate groups, are particularly efficient. The results are inter preted with the use of a recently proposed apatite dissolution model w hich assumes the formation, at the apatite interface, of an ionic semi permeable layer produced by the adsorption of calcium ions. According to this model, adsorbed polymers increase the ionic capacity of the in terface.