Papers by Author: David Shepherd

Abstract: The effect of substitution of zinc into the hydroxyapatite lattice(ZnHA) was evaluated using experimental precipitation studies and with ab initio modelling data. When attempting to introduce zinc into the hydroxyapatite (HA) lattice not all of the zinc is substituted and ICP confirms its presence in the supernatant. Modelling suggests that this is likely to be because of the high formation energy introducing zinc into the pure hydroxyapatite lattice, 4.6 - 4.9eV. In the experimental study it was found that a maximum of 0.61wt% zinc could be substituted into the HA lattice at 10oC with less being substituted at room temperature »22oC. Experimental measurements revealed that the presence of zinc in the lattice decreased the a-lattice parameter and increased the c-lattice parameter. Modelling showed that this was likely to be caused by the movement of the hydroxyl ions away from the c-axis, towards the zinc atoms which were substituted in calcium type II positions. The type II position was shown to be the most stable substitution site.

Abstract: Zinc substituted hydroxyapatite of varying wt% was produced using a precipitation method based on reacting calcium and zinc nitrate with ammonium phosphate. Characterisation results from X-ray diffraction (XRD) and X-ray fluorescence spectroscopy (XRF) showed that zinc was successfully substituted up to 0.8wt% using this method. Rietveld analysis showed that the alattice parameter was reduced and c-lattice parameter was increased with increasing zinc content. Initial mechanical test results showed samples with a zinc content of 0.4% had the greatest compressive strength.