SiCNO Coatings Enhance Endothelialization and Bactericidal activity and Reduce Blood Cell Activation

For biomedical applications, a number of ceramic coatings have been investigated, but the interactions with the components of living system remain unexplored for oxycarbonitride coatings. While addressing this aspect, the present study aims to provide an understanding of the biocompatibility of novel SiCNO coatings that could validate the hypothesis that such coatings may not only enhance the cell-material interaction by re-endothelialization but also can help to reduce bacterial adhesion and activation of blood cells. This work reports the physicochemical properties, hemocompatibility, endothelialization, and antibacterial properties of novel amorphous SiCNO coatings deposited on commercial pure titanium (Ti) by radiofrequency (RF) magnetron sputtering at varied nitrogen (N₂) flow rates. A comparison is made with diamond-like carbon (DLC) coatings, which are clinically used. The surface roughness, surface wettability, nanoscale hardness, and surface energy of SiCNO coatings were found to be dependent on the nitrogen (N₂) flow rate. Importantly, the as-deposited SiCNO coatings exhibited much better nanoscale hardness and scratch resistance than DLC coatings. Furthermore, Raman spectroscopy analysis of the SiCNO coating deposited on Ti showed a change in the graphitic/disordered carbon content. Cytocompatibility and hemocompatibility properties of the as-deposited SiCNO coating were evaluated using the Mus musculus lymphoid endothelial cell line (SVEC4-10) and rabbit blood in vitro. WST-1 assay analysis showed that these coatings, when compared to DLC, exhibited a better proliferation of endothelial cells, which can potentially result in improved surface endothelialization. Furthermore, qualitative and quantitative analyses of immunofluorescence images revealed a dense cellular layer of SVEC4-10 on SiCNO coatings, deposited at 15 and 30 sccm nitrogen flow rates. As far as compatibility with rabbit blood is concerned, the hemolysis of the SiCNO coatings was less than 4%, with slightly lower values for coatings deposited without N₂ flow. The SiCNO coatings support less platelet adhesion and aggregation, with no signature of morphological deformation, as compared to the uncoated titanium substrate or DLC coatings. Furthermore, SiCNO coatings were also found to be effectively extending the blood coagulation time for a period of 60 min. The antimicrobial study of as-deposited SiCNO coatings on E. coli and S. aureus bacteria revealed the effective inhibition of bacterial proliferation after 24 h of culture. An attempt has been made to explain the cyto- and hemocompatibility properties with antimicrobial efficacy of coatings in terms of the variation in the coating composition and surface energy. Taken together, we conclude that SiC_1.3N_0.76O_0.87 coating having a roughness of 17 nm and a surface free energy of 54.0 ± 0.7 mN/m can exhibit the best combination of hardness, elastic modulus, scratch resistance, cytocompatibility, hemocompatibility, and bactericidal properties.