Arthur Olivier Joseph Ganz
Topographic nanostructuring of surfaces is a promising concept, in particular to improve the bio-integration of titanium orthopedic implants. In this context, a new method for the nanostructuring of anodised titanium surfaces was developed. Ordered topographic features in the tens of nanometre in height were created by anodising electropolished titanium in the presence of polymeric particles deposited as monolayers. To do so, an existing electropolishing method for titanium was applied and optimised, allowing the production of extremely smooth starting surfaces. The particle-substrate contact was mesured, modeled and finally modified by plasma, thermal and chemical vapour treatments and its effect on the topography of the anodic oxide layer was investigated. Different types of ordered structures were produced, and characterised by atomic force microscopy (AFM) and scanning electron microscopy (SEM). The influence of the anodisation conditions on the topography and morphology of the surface was studied. To gain deeper understanding of the mechanisms at play, a model experiment using electron beam lithography was designed. Circular masks of increasing diameters were deposited on the surface to simulate the presence of particles of corresponding sizes, and the effect on the topography of the oxide layer was characterised. Some aspects of the structuring phenomena observed with the particles were thus cleared up, in particular the extent of oxide layer growth underneath the masks. Finally, numerical finite element modeling was applied to simulate the initial stages of anodic oxide growth around masks, leading to a better understanding of the formation of some of the topographic features observed. In parallel to this work on surface structuring, mesoporous silica particles containing different functional nanoparticles were produced. They were originally destined to serve as an alternative to the polymeric particles used to create our structurations. Their synthesis process, based on the formation of particles by sol-gel in a miniemulsion, was scaled-up and optimised to obtain narrowly distributed submicron particles with a high micropore volume and a high functional nanoparticle loading. These multifunctional particles were finally found to be unadapted for surface structuring but were assessed for various other applications, depending on the type of nanoparticles incorporated in the silica matrix. In combination with superparamagnetic iron oxide nanoparticles (SPIONS), they were evaluated as potential magnetic drug delivery vehicles. Drug loading and release of the anticancer drug paclitaxel was studied as a model system by simulation and experiment. The release kinetics was found to be very slow, restricted by the large chemical potential difference between the molecule in solution and the molecule adsorbed inside micropores. Chromium doped alumina (ruby) nanoparticles were synthesised and characterised for potential application as near-IR fluorescent markers for biomedical imaging. Their photoluminescent properties were studied and were found to be sufficiently intense for bright-field fluorescence microscopy and confocal laser scanning microscopy. They could however not be incorporated in the multifunctional particles during the gel emulsion synthesis. Manganese doped zinc sulphide quantum dots were also encapsulated in a mesoporous silica matrix and used as the basis material for the production of multicolour fluorescent surfaces. Localised laser thermal treatment of the material was successfully realised, causing a shift in its fluorescence emission wavelength. Multicolour fluorescent images could thus be drawn by programing the laser appropriately.
EPFL2010
