PECVD of silicon and titanium based coatings to enhance the biocompatibility of blood contacting biomedical devices

Abstract

The clinical success of a surgical implantation depends on various factors including the design and biocompatibility of the biomaterial, surgical procedure adopted, injuries made during implantation and health and condition of the patient. The success of a biomaterial depends on the interaction and the progressive reaction between the blood components and the surface of the implant. Proteins present in the blood will be the first components to become adsorbed on the surface of the biomaterial. Studies show that the protein fibrinogen present in the blood plasma is the major initiator of inflammatory reactions and involved in blood clotting. By minimizing the fibrinogen adsorption it is possible to reduce the contribution of the biomaterial surface characteristics to thrombosis and inflammatory reactions. In this work, silicon and titanium based thin film coatings with four different surface characteristics were deposited by PECVD on 316L stainless steel substrates. Polymer-like SiOxCyHz, silica-like SiOx, titanium oxide TiO, and silicon-titanium mixed oxide coatings were deposited by plasma decomposition of organic molecules. An extensive study was done on silicon based coatings deposited from hexamethyl disiloxane (HMDSO) to analyze the influence of plasma process parameters like RF power, precursor flow ratio and flow rate on the surface chemical and mechanical characteristics of the film. Titanium dioxide coatings deposited from titanium tetraisopropoxide (TIP) were also analyzed for the effect of plasma process parameters on their surface characteristics. Silicon - titanium mixed oxide coatings were deposited to obtain intermediate characteristics between silicon oxide and titanium oxide films and the process was optimized to get a hydrophilic surface with wettability lower than SiO, and a bandgap higher than that of titanium dioxide. It was concluded, from the fibrinogen adsorption studies, that both the film wettability and bandgap has to be optimized in order to minimize the fibrinogen adsorption