Deposition of calcium phosphate coatings with defined chemical properties using the electrostatic spray deposition technique

Abstract

The electrostatic spray deposition (ESD) technique was used for biomedical purposes in order to deposit calcium phosphate (CaP) coatings onto titanium substrates. The relationship between various deposition parameters and the chemical properties of deposited coatings was investigated in order to be able to deposit CaP coatings with tailored chemical characteristics. The results showed that the chemical properties of the coatings were determined by both physical, apparatus-related factors and chemical, solution-related parameters. By varying the processing parameters of the technique, several crystal phases and phase mixtures were obtained, ranging from carbonate-free phases such as meta- and pyrophosphates, monetite and various tricalcium phosphates to carbonate-containing phases such as various carbonate apatites and calcite. On the basis of these results, a chemical mechanism of coating formation was proposed. Essentially, the deposition of the various crystal phases was the result of an acid–base reaction between basic CO 3 2− groups (originating from solvent decomposition reactions) and acidic HPO 4 2− groups from an intermediate monetite (CaHPO 4) phase of the CaP precipitate. The amount of carbonate incorporation (ranging from 0 to 15 wt%) determined the crystal and molecular structure of the deposited coatings.