Artificial heart valves:: improved hemocompatibility by titanium oxide coatings prepared by ion beam assisted deposition

Abstract

Titanium oxide films were prepared by ion beam assisted deposition on an Eaton Z-200 system, in which the deposition of titanium evaporated from an electron beam evaporator and the bombardment with xenon ions at an energy of 40 keV extracted from an arc discharge-type ion source proceeded simultaneously in an O 2 environment. X-ray photoelectron spectroscopy (XPS), Rutherford backscattering spectroscopy (RBS) and X-ray diffraction (XRD) were used to characterize the deposited films. It was found that the atomic ratio of O/Ti is about 1.85:1. XPS analysis shows that Ti 2+, Ti 3+ and Ti 4+ chemical states exist on the titanium oxide films. The films deposited are in principle crystalline TiO 2 with a rutile structure. The films exhibit a highly (100) orientation and increase the degree of (100) orientation with ion beam current density decreasing. The blood compatibility of titanium oxide films was studied by in vitro and in vivo investigation. In vitro investigation includes clotting time measurement and platelet adhesion. Clotting time measurements show that the clotting time of titanium oxide films is longer than that of low temperature isotropic pyrolytic carbon (LTI-carbon), which is widely used as artificial heart valves in clinics. There are also fewer platelets adhered to and deformed on the titanium oxide films compared to the LTI-carbon. In vivo investigation, implanting LTI-carbon and titanium oxide coated LTI-carbon into the ventral aorta of a dog for two weeks, shows that the amount of thrombus on titanium oxide coated LTI-carbon is only about 1/8 compared to that of LTI-carbon. The relationship between chemical states and blood compatibility was discussed. We think that the existence of Ti 2+ and Ti 3+ is beneficial for blood compatibility.