| Blood compatibility is the key requirement for blood-contacting devices, and it relates mainly to the thrombotic response induced by the materials. Titanium oxide (TiO2) thin film is a potential candidate for the surface modification of blood-contacting devices because of its resistance to corrosion and good blood compatibility. Obviously, it is important to improve the antithrombotic capacity of TiO2 films further to obtain better blood compatibility. As a photocatalyst, Ultraviolet light (UV) irradiation can change the chemical properties of TiO2 surface, which may affect the anticoagulant ability of TiO2. However, the effect of UV-irradiated TiO2 films on blood compatibility has rarely been reported.This study attempts to (1) determine the effect of UV-irradiation on the anticoagulant ability of anatase TiO2 films (Chapter 2), (2) detect the mechanisms of the anticoagulant ability of the UV-irradiated TiO2 films (Chapter 3 and 6), and (3) explore the applications of the UV-irradiated TiO2 films in the region of biomaterials (Chapter 4,5 and 6). The following conclusions are obtained according to the results coming from the research mentioned above: 1. UV-irradiation significantly improves the blood compatibility of anatase TiO2 films, by suppressing fibrinogen adsorption and platelet adhesion, and showing no harm to red blood cell. Since the anticoagulant ability of UV-irradiated anatase TiO2 films (UV-TiO2) is even better than low-temperature isotropic pyrolytic carbon (LTIC), UV-TiO2 can be used in improving the blood compatibility of the blood contact devices. 2. In this study, we explored the mechanisms of the anticoagulant ability of UV-TiO2, and found that:(1) The photogenerated ROS was related to the improvement of the anticoagulant ability of UV-TiO2. The gengereation of the ROS was depended on the existence of O2 gas and photogenerated free electron (e-), which had oxidation ability and can diffuse on the solid surface or in air. Therefore, UV irradiation affected the anticoagulant ability of TiO2 films in a time-dependent manner. (a) UV irradiation on TiO2 films for short duration (e.g.1 min) evidenced a suppression effect on fibrinogen adsorption and platelet adhesion. (b) When the UV irradiation time was longer, this suppression effect extended from the surface of the UV-irradiated TiO2 films to the surface of the adjacent masked TiO2 films and the nearby Si surface. (c) A prolonged UV irradiation time (e.g.240 min) may enhance the fibrinogen adsorption of and platelet adhesion to TiO2 films. However, when comparing the enhancement effect and the suppression effect, the results showed that the latter was the main one to influence fibrinogen adsorption of and platelet adhesion to TiO2 films.(2) The good anticoagulant ability of UV-TiO2 could not be the result of the retained ROS, photo-induced super-hydrophilicity, increased hydroxyl groups (-OH) number, or decomposition of the adsorbed hydrocarbon. The anticoagulant ability was stable in ethanol and acetone, but not in the high tempretuer. It also can be destroyed by scratching with a stainless steel tweezers.(3) after contacting with blood, a bioinert surface was formed on the UV-TiO2, which inhibited the subsequent protein adsorption and cell adhesion. Additionally, the forming of the bioinert surface was abolished when the UV-TiO2 contact with the saline solution of the adhesive protein firstly. 3. Fabricated a positive charged and anticoagulant TiO2 film (TiO2-H2SO4-UV) by using the sulfuric acid and UV-irradiation, which can suppress the platelet adhesion and fibrinogen adsorption while improve the adhesion and spreading of cells in vitro. However, animal experiment is needed to determine whether the two conflicting effects could coexist in vivo. 4. The using of UV-TiO2 in micro-fabrication of biomaterials was also studied in this thesis:(1) The fibrinogen micropattern was obtained on the partially UV-irradiated TiO2 surface, which can altering the adhesion of the platelet, endothelial cells (ECs) and smooth muscle cells (SMCs) to produce the cells array.(2) The TiO2-TiN micropattern was fabricated and treated by UV-irradiation. The adhesion of platelets on the TiN region was found to be suppressed, which could be related to the diffused ROS which generated on the nearby TiO2 surface.(3) The TiO2-TiO2 micropattern with several micrometers in depth was fabricated. After a relatively long time of UV-irradiation, the adhesion of platelets was suppressed, while the adhesion of ECs was improved on the micropatterned surface. Additionally, the shape of ECs was prolonged by the micropatterned surface.5. The photocatalytic lithography (PCL), which based on the photogenerated ROS from the TiO2 under UV-irradiation, was used as a new method to improving the anticoagulant ability of and pattering protein and cells on various materials. The improving mechanism of anticoagulant ability on materials treated by PCL was similar with the TiO2 treated by UV-irradiation. Therefore, PCL could not improve the anticoagulant ability of the materials with antioxidant properties. |
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