| Research and development in the biomedical materials, according to materials used in different parts in vivo, its biocompatibility have different requirements. The materials in contact with blood, their blood compatibility are mainly considered.As the biomaterials,316L stainless steel and NiTi alloy are commonly used to manufacture medical devices in contact with blood such as intravascular stent. However, they can result in problems such as thrombus and ion exudation in a physiological environment, which has attracted great attention.It is generally believed that Ca2+, fribrinogens, platelets and erythrocytes in blood play important roles in thrombosis and will not coagulate without Ca2+. Generally, these bio-particles and Ca2+ can have the effect of weak diamagnetic and the forces associated with this property making possibly the levitation of these particles. Therefore, a new method was suggested to settle thrombus problem in this thesis:we can establish a micro-magnetic field at the surface of biomaterial and thus the distribution of these particles adjacent to the surface can be modified when the biomaterial is put into the blood, resulting in reduced or restrained contact between these particles and biomaterials.The execution method:①The SrFe12O19 ultrafine powders were prepared by sol-gel method.②TiO2 film containing SrFe12O19 was coated on the surface of NiTi alloy and 316L stainless steel by sol-gel method.③The effecting of different kinds of substrates and film, different content magnetic powders on the blood compatibility were studied.The formation process, the structure and surface morphology of SrFe12O19 powders, the formation process, surface composition, structure and morphology of the films were studied by X-ray Diffraction(XRD), Transmission Electron Microscopy (TEM) and Scanning Electron Microscope(SEM) etc. The magnetic performance of ferrite was measured by HH-15 vibrating sample magnetometer (VSM). The interface adhesive strength between the film and substrate was measured by scratching test. The component and the roughness of film were studied by XRD and surface roughness measuring instrument. The corrosion resistance of the films was studied by the number of releasing toxic ions in Simulated Body Fluid (SBF). Additionally, the blood compatibility was primarily evaluated by dynamic clotting time, hemolysis and blood platelet adhesion test. Pure SrFe12O19 magnetice powders with average dimension of 20-50nm were obtained by sol-gel route. The morphologies of powders were hexagon and sphere. The magnetic hysteresis loops of SrFe12O19 were tested. Results indicated that magnetic powders heated at 850℃for 1h then heated to 950℃had good magnetic performance. Coercive force, saturation intensity and residual magnetization of powders mentioned above were 2275.45Oe,99.95emu/g and 30.39 emu/g respectively.According to optimum process, TiO2 film containing SrFe12O19 was coated on the surface of NiTi alloy and 316L stainless steel by sol-gel method. Titanium butoxide (Ti(OC4Hg)4) was used as the starting material, ethanol as solvent, chlorhydric acid and acetylacetone as additives, respectively. The results showed that crystal structure of TiO2 film heated at 500℃for 1h was anatase-type. The crystal grains were refined and the film became dense at slow heating speed (1～2℃/min). The results of scratching test showed that the interface adhesive strength between the film coating SrFe12O19 and 316L stainless steel and NiTi alloy substrate is about 27N, 30N, respectively. This result indicated that TiO2 film coating with SrFe12O19 have little influence on the bond strength of film-matrix.The results of corrosion experiment indicated that the corrosion of metallic materials by SBF could be reduced by TiO2 film containing SrFe12O19 on NiTi alloy and 316L stainless steel and the precipitating toxic Ni ion could be prevented. The result of dynamic clotting time test showed that dynamic clotting time of 316L stainless steel and NiTi alloy was increased with TiO2 film containing SrFe12O19, and the more magnetic powders the better of anticoagulant performance. The TiO2 film contained SrFe12O19 would have lower hemolysis rate, which would reduce wrecking degree of hemocyte caused by micromagnetic field, and the blood compatibility would be improved. The blood platelet adhesion test illuminated that the film contained SrFe12O19 has good blood compatibility, the number of the blood platelet adhered to film was lower than the surface of the substrate, the filopodium growth of blood platelet is not obvious. Based on experiments analysis,mechanism of effect of micro-magnetic field at the surface of biomedical metallic materials on blood compatibility was discussed.
|
PDF Full Text Request