Study On The Surface Fibrinolytic System:Mechanism And Construction On Coronary Stent

Foreign materials induced or endothelial injury induced thrombosis remains a severe problem in the development of blood contact devices. Prevention of coagulation appears not to be possible when a foreign surface is in contact with blood; the alternative concept of a clot lysing surface has therefore been suggested. The concept is to mimic the naturally occurring fibrinolytic process that occurs on the surface of fibrin. The key point to realize this concept is to design the surface to adsorb preferentially from blood the essential components of the fibrinolytic system and a plasminogen activator (e.g. tissue plasminogen activator, t-PA) which interact to generate the clot dissolving enzyme plasmin. Lysine, with free ε-NH2and-COOH groups, has been proven to possess affinity to plasminogen and t-PA. Therefore, surfaces with incorporation of such lysine would have the potential to realize fibrinolytic surfaceThe main focus of this thesis is to build a surface with fibrinolytic activity through incorporation of ε-lysine and to analyse the interaction between the surface and plasminogen. On the basis, a mimic of the fibrinolytic system was constructed on L605cobalt-chromium coronary stents to dissolve the nascent clot formed on it. The detailed research works are introduced as follows:First, the preparation of ε-lysine and a-lysine modified gold surfaces, and the investigation of the interaction between plasminogen and the two surfaces were introduced. The dipeptides CK1and CK2, containing ε-lysine and a-lysine respectively, were immobilized via self-assembly method. The surface properties were investigated by contact angle meter and ellipsometry. Plasminogen adsorption on the two lysine derived surfaces was evaluated using ELISA method confirming that ε-lysine can capture plasminogen selectively from plasma. And kinetics of the interaction between plasminogen and lysine derived surfaces were analyzed using SPR. The results suggested that the ε-lysine modified gold surface showed higher association rate constant and lower dissociation rate constant for plasminogen which further confirmed that ε-lysine possesses a higher affinity to plasminogen. In addition, the results of plasmin activity assay also indicated that plasminogen bound on ε-lysine surface showed higher enzymatic activity than on the other one.Then ε-lysine was attached to coronary stents (L605) using poly(2-hydroxyethyl methacrylate)(poly(HEMA)) as a spacer for mimicking the fibrinolytic system on real blood contact materials. HEMA was grafted from L605stent via atom transfer radical polymerization (ATRP) to prevent non-specific protein adsorption and increase the grafting density of lysine. The lysine-poly(HEMA) modified stent was shown to have low nonspecific protein adsorption and to bind plasminogen in high quantity from plasma. Following exposure to plasma and treatment with tissue plasminogen activator, the lysine-modified stents showed clot-lysing properties in vitro while the unmodified L605stents did not. It was shown that the modified stents retained their clot lysing properties after24h exposure to plasma. The nascent clot lysis approach thus appears to warrant further research as a means to overcome the problem of thrombosis in intravascular stents.