Synthesis of calcium phosphate thin layers of increased biological activity by chemical growth in simulated body fluids

We studied the chemical growth of calcium phosphate nanostructured coatings onto silicon wafers pre-covered with carbonated polycrystalline hydroxyapatite films. Silicon wafers were covered with hydroxyapatite thin layers by radio frequency magnetron sputtering and then immersed in 37 deg C simulated body fluids for up to 20 days. Immersed structures were extracted every 2 days for studies by Fourier transform IR spectrometry. The chemically grown layers were further analyzed by X-ray diffraction and scanning electron microscopy. The growth kinetics of calcium phosphate deposits was monitored by estimating the area of phosphate, carbonate and water stretching bands of the recorded infra-red vibrational spectra. Sequential annealing in vacuum up to 950 deg C was applied to elucidate the nature of incorporated water. Our studies revealed that the layers growing in simulated body fluid are rougher than initial hydroxyapatite interlayers, contain carbonates, include water in interlayer's voids and have therefore an increased biological activity for promoting faster implants integration with human bone tissues.