Structural and chemical changes to plasma sprayed hydroxyapatite coatings in simulated body fluid

This prospective study assesses the biological behaviour (bioactivity) of calcium phosphate coatings in a physiological environment. The structural and chemical changes occurring in plasma sprayed hydroxyapatite coatings were investigated by soaking the coatings in simulated body fluid (SBF) for a period of up to 3 weeks. Microstructural changes to coatings were analysed by X-ray diffraction (XRD) using Rietveld analysis with a fundamental parameters approach. Fourier Transform infra-red spectroscopy (FTIR) and scanning electron microscopy (SEM) were used for further chemical and morphological examination. Our results show that with immersion time the amorphous calcium phosphate (ACP) preferentially dissolves followed by the precipitation of carbonated apatite. There is a increase in diffraction peak broadening and hence crystallite size and microstrain. Due to the increase of crystal anisotrophy with immersion time, it is not possible to separate the components by the Williamson-Hall method. Rietveld analysis has highlighted subtle changes in the lattice parameters of the coatings. The contraction of the c-axis and increase in the a-axis confirms that inclusion of foreign ions has occurred in the crystal lattice.