Influence of Titanium Dioxide Grain Size on Phasic Composition and Lysozyme Adsorption of Hydroxyapatite and Titanium Dioxide Composite Powders-A Thermal Decomposition Study by XRD and SEM Analysis

Biomedical applications make high demands on the development of novel bioactive materials, which are often based on functionalized calcium phosphates (CaPs). In this study, pure nanoscaled hydroxyapatite (HAp) and modified HAp with titanium dioxide (TiO2) with both nano- and microparticles are successfully synthesized from the reactants calcium hydroxide and orthophosphoric acid in a wet chemistry reaction. The obtained powders are sintered in a temperature range of 750 degrees C-1400 degrees C to study their thermal decomposition behavior. The phase composition and the surface morphology are characterized using X-ray diffraction, scanning electron microscopy, and energy dispersive X-ray spectroscopy with element mapping. Lysozyme adsorption experiments reveal significantly higher adsorption on the samples modified with nanoparticles. Sintered samples modified with both TiO2 particle sizes show HAp decomposition to beta-tricalcium phosphate (beta-TCP) as well as the formation of perovskite (CaTiO3) in different portions depending on the TiO2 particle size. TiO2 nanoparticles support anatase to rutile transformation at lower temperatures than TiO2 microparticles. The results show that the examined HAp/TiO2 composites may serve as a starter material for tailormade biomaterials with specific composition by variation of the sintering temperature and the TiO2 particle size.