In Vitro Biodegradation of a-C:H:SiO x Films on Ti-6Al-4V Alloy.

This paper focuses mainly on the in vitro study of a five-week biodegradation of a-C:H:SiO _x films of different thickness, obtained by plasma-assisted chemical vapor deposition onto Ti-6Al-4V alloy substrate using its pulsed bipolar biasing. In vitro immersion of a-C:H:SiO _x films in a solution of 0.9% NaCl was used. It is shown how the a-C:H:SiO _x film thickness (0.5-3 µm) affects the surface morphology, adhesive strength, and Na ⁺ and Cl ^- precipitation on the film surface from the NaCl solution. With increasing film thickness, the roughness indices are reducing a little. The adhesive strength of the a-C:H:SiO _x films to metal substrate corresponds to quality HF1 (0.5 µm in thickness) and HF2-HF3 (1.5-3 µm in thickness) of the Rockwell hardness test (VDI 3198) that defines strong interfacial adhesion and is usually applied in practice. The morphometric analysis of the film surface shows that on a-C:H:SiO _x -coated Ti-6Al-4V alloy surface, the area occupied by the grains of sodium chloride is lower than on the uncoated surface. The reduction in the ion precipitation from 0.9% NaCl onto the film surface depended on the elemental composition of the surface layer conditioned by the thickness growth of the a-C:H:SiO _x film. Based on the results of energy dispersive X-ray spectroscopy, the multiple regression equations are suggested to explain the effect of the elemental composition of the a-C:H:SiO _x film on the decreased Na ⁺ and Cl ^- precipitation. As a result, the a-C:H:SiO _x films successfully combine good adhesion strength and rare ion precipitation and thus are rather promising for medical applications on cardiovascular stents and/or friction parts of heart pumps.