Incorporation of fluorine ions into hydroxyapatite by a pH cycling method.

Fluorine ions were incorporated into hydroxyapatite (HA) using a pH cycling method and the resulting materials were studied using transmission electron microscopy (TEM), X-ray diffraction (XRD), and electrochemical analysis. TEM observations showed that fluoridated hydroxyapatite (FHA) nanoparticles with a narrow particle size distribution were obtained at several different levels of fluorine incorporation. Significant particle growth was observed following calcining at 1200 degrees C. The TEM data revealed that, instead of forming laminated structures, a mixture of HA and FA was obtained, and that this mixture transformed into a single homogeneous FHA phase upon heating. It was found that the efficiency of fluorine incorporation did not vary significantly with the initial HA particle size, but increased as the fluorine content of the initial solution was increased. A relatively low fluorine incorporation efficiency, approximately 60%, was attained for most of the FHA samples and this was attributed to the short holding time at each pH cycle and the limited number of pH cycles employed in the current study.