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DLC and CVD diamond coated Si3N4 ceramics for tribological and biomedical purposes

Final Activity Report Summary - BIO-TRIBODIAM (DLC and CVD diamond coated Si3N4 ceramics for tribological and biomedical purposes)

The work done and results obtained under the project were:

- In order to improve the tribological behaviour and to provide efficient full sealing conditions, the coating of silicon nitride (Si3N4) ceramic surfaces with a solid lubricating diamond-like carbon (DLC) film was tested in self-mated configuration. DLC-coated Si3N4 rings showed an ultra-high performance as mechanical seals.

- Reciprocating ball-on-flat sliding tests were performed to characterise the DLC coated Si3N4 against UHMWPE tribopair. The sliding occurred under dry conditions and simulated body fluid (SBF) lubrication ambient conditions in order to simulate the environment of a hip joint articulated prosthesis. Results demonstrated that the friction coefficient is almost constant during the running-in period without delamination of the DLC coating.

- DLC coatings are of enormous interest for biotribological applications due to their biocompatibility, auto-lubricious, and non-stick properties. MG63 osteoblast-like cells showed poor adhesion on DLC films but the adherent cells displayed a normal morphology and, as compared to standard polystyrene tissue culture plates, exhibited a higher cell growth rate, suggesting no indication of cytotoxicity.

- A correlation between the generation of extrinsic defects and the stress produced by the thermal expansion coefficient mismatch between CVD polycrystalline diamond films and the substrate material has been established. Defect creation in diamond can be controlled by the modification of substrate composition to influence the generation of extrinsic stresses due to thermal coefficient mismatch.

- A new approach to deposit commercial pure Titanium or a multi-component coating, made of commercial pure Titanium and Hydroxyapatite onto UHMWPE, by DC Magnetron sputtering and DC/RF Magnetron co-sputtering, respectively was accomplished. This approach is useful on the development of a novel acetabular component in which the metallic shell is substituted by a coating and, therefore, made of just one piece.

- Deposition of boron nitride films by RF magnetron sputtering was performed envisaging enhancing the wear resistance and ferrous materials cutting performance of industrial components. The deposition parameters were studied finding out that the working gas produces a changing of the stoichiometry of the films and it causes a peak shift. The peak shifts are also to relate to the surface finishing of the substrate.