Aqueous sol gel derived titania and modified titania for biomedical applications

The aim of this work is to present the development of an aqueous sol-gel route to provide titania thin films and bulk materials, which enable the effects of modifying elements to be readily studied and investigated. Modifying elements of aluminium and/or vanadium were investigated and their consequential interactions studied in order to gain further understanding of their influence and possible applicability as candidate biomaterial coatings and surfaces. Aqueous sol-gel derived unmodified titania, aluminium and vanadium modified titania and aluminium-vanadium co-modified titania were studied both as bulk materials and thin films deposited on commercially pure (c.p.) titanium. The work describes the preparation, characterisation of the chemical and physical properties of the materials and finally draws parallels between the bulk materials and the deposited thin films as a function of calcination temperature. Modification of the titania was achieved through the preparation of six different systems which incorporated 4 wt %, 8 wt % and 16 wt % vanadium, 6 wt % and 12 wt % aluminium and 4 wt %, 6 wt % vanadium-aluminium, respectively. A detailed study of the physical and chemical nature of unmodified titania as an 'as-prepared' sol, bulk material and deposited thin films highlighted the effects, both chemically and physically, of thermal processing (333K - 1273K). Analysis was performed by a range of analytical techniques including Photon Correlation Spectroscopy (PCS), Powder X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM), Reflection High-Energy Electron Diffraction (RHEED), Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM). The subsequent results illustrated both bulk and thin film phase transformation temperatures of the titania as well as physical evolutionary effects on the bulk material and thin films. The data has acted as a reference in order to ascertain the subsequent effects of the modifying element(s). Further work, utilising the various modifying element(s) and various concentrations of modifying element(s), presented significant effects as a function of thermal processing temperature of the 'as-prepared' sols and both the bulk materials and thin films. With increasing amounts of vanadium and/or aluminium follows an increase in the agglomerate size distribution in the 'as-prepared' sol. During thermal processing of the bulk materials and thin films it was demonstrated that vanadium destabilised the anatase phase by some 150 deg, irrespective of concentration. Solid solution by vanadium (V4+) ions was observed in the rutile lattice and an accelerated growth of the titania crystallites. Phase separated V2O5 (Shcherbinaite) was also noted in the 8V/TiO2 (823K-1073K) and 16V/TiO2 (773K-1173K) materials. In contrast, aluminium had the opposite effect as it stabilised the anatase phase. This stability was further increased with increasing concentrations of aluminium. No solid solution was observed in either the anatase or rutile phases and the titania crystallite growth was retarded. Phase-separated α - Al2O3 (Corundum) was shown to exist over a range of temperatures (6AI/TiO2 (1073K-1373K), 12AI/TiO2 (1173K-1373K)). Co-modified titania also behaved in a similar manner to aluminium modified titania. The aluminium had the dominating effect on the phase-transformation and crystallite growth and again no solid solution was observed nor any separation of phase(s). Phase transformation temperatures in the bulk materials were mirrored in the deposited thin films in all cases indicating that the modifying element effects not only the deposited thin film but also the naturally grown oxide layer which forms during calcination. However, no phase-separated alumina or vanadia was observed. Trends in surface roughness demonstrated that calcination temperature had a dominating effect on the surface roughness and that only a negligible effect was observed with respect to modifying element(s). Overall, this work provides a basis for future sol-gel coating applications utilising other modifying elements commonly found in implant alloys or determined to enhance the biological response of the implant. (author)