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A study was carried out on the consequences of the -OH(surf)/F(-) exchange occurring at the surface of TiO(2) P25 when suspended in HF/F(-) solutions. The maximum extent of fluorination was reached at pH 3.0, resulting in the fixation on the surface of ca. 2.5 F(-)/nm(2). The surface features of fluorinated samples under two selected conditions were investigated by IR spectroscopy, in comparison with pristine TiO(2). The collected data suggested that bridged -OH(surf), likely located on regular facets, was more resistant to exchange with F(-). Combined high resolution transmission electron microscopy (HRTEM), inductively coupled plasma mass spectrometry (ICP-MS) and IR measurements indicated that the fluorination performed in the adopted condition did not induce any etching of TiO(2) particles, and the -OH(surf)/F(-) exchange appeared reversible by treatment in concentrated basic solutions. Furthermore, fluorination resulted in an increase of the Lewis acid strength of surface Ti(4+) sites, which, as a consequence, retained adsorbed water molecules even after outgassing at 423 K. Such an effect involved the overwhelming majority of cations exposed on regular facets.

Titanium and its alloys represent the gold standard for orthopaedic and dental prosthetic devices, because of their good mechanical properties and biocompatibility. Recent research has been focused on surface treatments designed to promote their rapid osteointegration also in case of poor bone quality. A new surface treatment has been investigated in this research work, in order to improve tissue integration of titanium based implants. The surface treatment is able to induce a bioactive behaviour, without the introduction of a coating, and preserving mechanical properties of Ti6Al4V substrates (fatigue resistance). The application of the proposed technique results in a complex surface topography, characterized by the combination of a micro-roughness and a nanotexture, which can be coupled with the conventional macro-roughness induced by blasting. Modified metallic surfaces are rich in hydroxyls groups: this feature is extremely important for inorganic bioactivity (in vitro and in vivo apatite precipitation) and also for further functionalization procedures (grafting of biomolecules). Modified Ti6Al4V induced hydroxyapatite precipitation after 15 days soaking in simulated body fluid (SBF). The process was optimised in order to not induce cracks or damages on the surface. The surface oxide layer presents high scratch resistance.

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In Part I, the processing, microstructure and mechanical properties of three silicon nitride-based ceramics were examined and their non-toxicity was demonstrated. In this Part II, some features critical to biomedical applications were investigated: (i) the wetting behaviour against aqueous media, including physiological solutions; (ii) the chemical stability in water and in physiological solutions; and (iii) the wear resistance, measured under experimental procedures that simulate the conditions typical of the hip joint prosthesis. The results confirmed that silicon nitride may serve as a biomaterial for bone substitution in load bearing prosthesis.