Study On Preparation And Properties Of NO-Releasing Polyurethane

Biomaterials are widely used to resolve pathologies that cannot be corrected either by the natural healing process or traditional surgery. A haemocompatible biomaterial is one that can not induce adverse reactions such as blood clots when contact with blood. A large number of polymeric materials are currently employed to prepare various blood or tissue-contacting medical devices, but they will cause serious complications for patients, and ultimately induce function failure when contacting with blood and tissue.Nitric oxide (NO) can inhibit platelet adhesion, aggregation, and activation as well as relax smooth muscles and modulate neurotransmission. Polymeric materials that can release NO locally may effectually reduce platelet adhesion, aggregation, and thrombus formation, so NO-releasing polymers are prepared by different methods in recent years. In this thesis, L-cysteine was covalently immobilized onto polyurethane (PU) surface, and the modified material can catalyse endogenous NO for NO release. There are various NO-donors such as S-nitrosothiols and nitrites in body, NO bound to these substances in human plasma can be transferred to L-cysteine attached on the PU through transnitrosation. S-nitroso-L-cysteine (CySNO) is very unstable and will release NO rapidly in blood, then inhibits platelet adhesion and thrombus formation.In this study, fluorescent labeling was selected to qualitatively analyze L-cysteine attached on the polymers. BCA was used to measure the quatity of L-cysteine. NO releasing in simulant state was observed by 2,3-diaminonaphthalene fluorescence spectrophotometry. Wettability and surface topography of modified PU films were measured by contact angle meter and SEM. The hemocompatibility of modified PU films was evaluated using hemolysis test and the dynamic blood clotting test.The test results indicatethat the immobilization of L-cysteine onto PU films was successful, and activity of sulfhydryl group was reserved. Distribution density of L-cysteine onto PU films was 15.3nmol/cm~2. Wettability and surface topography of PU films was almostly unchanged before and after modification. The simulant test results showed the releasing quatity of NO was 1.06 nmol/cm~2 within 3h. Hemolysis test and the dynamic blood clotting test showed the blood compatibility of modified PU film could be improved. Therefore NO-releasing polyurethane is expected to be an ideal blood compatibility material used in clinical.