Reactivity of plasma-sprayed wollastonite coating in simulated body fluid.

We incubated wollastonite coatings prepared with plasma spraying in simulated body fluids for different periods to investigate the reactivity. The surface structures of wollastonite coatings immersed in simulated body fluids were analyzed with scanning electron microscopy, Auger electron spectroscopy, and transmission electron microscopy. The results showed a carbonate-containing hydroxyapatite layer formed on the surface of a plasma-sprayed wollastonite coating soaked in simulated body fluids, and a silica-rich layer appeared on the surface of the coating before the formation of the carbonate-containing hydroxyapatite layer. The formation mechanism of apatite on the coating surface could be explained in terms of the ionic exchange between H(+) within simulated body fluids and Ca(2+) in the coating, which resulted in an increase in the ionic activity product of the apatite in simulated body fluids and provided a specific surface with a lower interface energy to the formation of apatite nuclei.