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Zirconia is the most common ceramic used in dental implants. Even if it possesses both mechanical strength and esthetics, its intrinsic bio-inertness often results in a lack of biological integration. On the other hand, Si3N4 has been proved to be bio-active and to be able to easily osteointegrate. In this work, a Si3N4 powder-based laser-cladding process has been developed in order to improve the biological response to biomedical zirconia. The process resulted in the formation of a composite coating with Si3N4 particles dispersed in nano-crystalline/amorphous silicon. Microscopic observation showed that the layer is adherent to the substrate. The application of the laser cladding treatment resulted in an increase of the roughness, further enhancing the probability of interaction with biological tissues and consequently the bioactivity. Testing with human osteosarcoma cell lines resulted in the formation of bone tissue with high collagen maturity, high carbonate to phosphate ratios and good tissue mineralization, but lower cell proliferation when compared to stoichiometric Si3N4. The bone tissue quality parameters, as measured by Raman spectroscopy, resulted to be comparable to healthy human bone tissue and suggest that laser-cladded Si3N4 treatments might be able to improve the stability of zirconia implants.

Despite being the most used ceramic biomaterial in hip joint prosthesis, Zirconia Toughened Alumina (ZTA) is liable to undergo several degradation mechanisms in vivo, which might drastically affect its structural performance over time. Our standing point in this investigation was that neither in vitro tests nor finite elements simulations are yet capable to fully reproduce the complexity of the in vivo conditions. Through accurate analyses of retrievals, we attempt to add more pieces to the puzzle of in vivo loading history and to obtain better insight into the ZTA degradation mechanisms. For doing so, we applied a previously established automated scanning protocol to investigate the coupling between a ZTA femoral head and its metal stem counterpart in a short-term (20 months) retrieved hip implant. Metal contamination on the ZTA surface was severe and polymorphic transformation widespread on the whole surface of the taper, though reaching different values depending on the specific zone of the taper. Clear signs of third body abrasive wear and fatigue crack initiation could be found by means of laser and electron microscopies, and X-ray spectroscopy. Highly resolved mapping by Raman micro-spectroscopy revealed very high monoclinic fractions and pronounced residual stress magnitudes despite the relatively short in-vivo lifetime. Keywords: Zirconia-toughened alumina, Confocal Raman spectroscopy, Phase transformation, Metal contamination, 3D-CAD

Following the rising interested on 3D-printing technologies, this research explores the possibility to apply nitride-polymethylmethacrylate composite coatings on 3D printed parts in order to increase their resistance to bacteria colonization. Four different nitrides were tested: silicon, zirconium, hafnium and aluminum. Trans-micrometric particles of hafnium nitride (average size 1 µm) could be dispersed better than the other three nitrides (average size between 8 and 10 µm), but the chemical analysis confirmed that the former, due to the higher surface area, are more prone to spontaneous oxidation in air. After deposition, the surface of the various coatings contained between 40% (silicon nitride) and 90% (hafnium nitride) of exposed ceramic particles. All composite materials showed antibacterial effects when compared to standard polymethylmethacrylate, with hafnium nitride being the most effective against E. coli and aluminum nitride against S. epidermidis. It has been postulated that while Si3N4 long-term antibacterial effects are granted by the constant dissolution of the SiO2 surface layer, zirconium and hafnium composites are effective because they possess antibacterial properties both in their nitride and oxide forms.

The purpose of this work is to establish a protocol, which combines CAD modeling to non-destructive microscopic techniques of confocal Raman micro-spectroscopy and laser microscopy, to assess the in-vivo hydrothermal stability of ZTA femoral head retrievals. The combined effects of wear, biological environment, and in vivo occurring peculiar events as metal staining were evaluated on five retrieved ZTA femoral heads with implantation time ranging from 9 to 106 months. The protocol relies on the application of a polar grid on the entire surface of the head, which divides it into small sectors; each sector is then automatically screened with micrometer resolution. Maps are finally linked to each other and an in-toto view of the retrieved head becomes available in three dimensions. Upon combining analytical techniques with a solid modeling computer-aided design (CAD) software, it becomes possible to develop a 3D model of the femoral head, which comprehensively describes topographic, crystallographic, and micromechanical characteristics of the entire surface and immediate sub-surface. The combination of CAD, polarized Raman spectroscopy, and laser microscopy has led to in-toto screening of femoral head with micrometer-scale resolution, thus providing a new and comprehensive protocol for both quality assessments on new components and failure analysis on retrievals. Keywords: Zirconia-toughened alumina, Confocal Raman spectroscopy, Phase transformation, Metal contamination, 3D-Cad

Anodic spark deposition is particularly spread as coating treatment of titanium in biomedical applications, as it allows to improve both durability and biocompatibility of titanium and its alloys. This work proposes an analysis of different surface treatments on titanium, where surface etching in HF prior to anodizing and final alkali etching of the anodic oxide are chosen as possible methods to alter surface roughness, crystal structure and chemical composition. Anodizing was performed at two different voltages to produce different morphologies and crystal phases. Larger and more regular porosity was obtained at higher voltages, together with the formation of sodium titanates. While the HF pre-treatment only affected surface roughness but not surface chemistry, the NaOH post treatment promoted the formation of Na2TiO3 especially on high voltage formed oxides. This was identified as the cause for a larger presence of radical species, which modify surface bioactivity and is responsible for a bacteriostatic effect of the treatments reported in previous biological studies. Keywords: TiO2, Anatase, Anodic spark deposition, Raman spectroscopy, Na2TiO3