Lambrecht Lk

Polyether-urethane ionomers: surface property/ex vivo blood compatibility relationships

Abstract The effect of incorporation of ions into polyurethanes on their interfacial interaction with blood is of interest because of the relative blood compatibility of polyurethanes, and the effect of ionic domains on surface properties and thus blood response. A series of uncharged, anionic, cationic, and zwitterionic polyetherurethanes was coated on tubing surfaces, and their blood response determined using an ex-vivo canine series shunt experiment. The results showed the polyurethane zwitterionomer and anionomer to be more thromboresistant than the uncharged polyurethane. The polyurethane cationomer was the most thrombogenic material studied. A comparison between two uncharged polyurethanes of different hard segment content showed that surface soft segment concentration correlated with thromboresistance. Multiprobe surface characterization using contact angle measurements, ESCA, ATR-IR, and SEM were used to obtain surface property information on the materials studied. The thromboresistance of the zwitterionomer and the anionomer was related to a high concentration of the mobile side chain ionic sulfonate group at the surface. Ionic mobility at the interface appears to strongly influence the blood response of these materials. Ionization of polyurethanes is thus a useful technique to both improve blood compatibility and study the role of surface chemistry in artificial surface-induced thrombosis.

The influence of preadsorbed canine von Willebrand factor, fibronectin and fibrinogen on ex vivo artificial surface-induced thrombosis

We have examined the effects of preadsorption of several canine plasma proteins on surface-induced thrombogenesis in a canine ex vivo model. Our technique allowed determination of initial deposition and subsequent embolization of 51Cr-labeled platelets and 125I-fibrinogen onto and from polymeric arterio-venous shunts in non-anticoagulated canines. Segments of the tubing were removed at various time points between 2 and 120 minutes of blood contact for examination of the morphology of the thrombus by scanning electron microscopy. Thrombus deposition was measured on uncoated plasticized poly(vinyl chloride) (PVC) and PVC precoated with canine von Willebrand factor (vWF), fibronectin, partially purified fibrinogen (fibrinogen which contained vWF and fibronectin as impurities), or purified fibrinogen (fibrinogen which had been further purified to remove fibronectin and vWF). Preadsorption of all proteins studied enhanced the thrombogenic response relative to that of the uncoated surface. Precoating with vWF or partially purified fibrinogen resulted in the deposition of the greatest number of thrombi, and embolization was slower than on shunts precoated with canine fibronectin or purified fibrinogen. The deposition-embolization profiles for the fibronectin and purified fibrinogen-coated surfaces were similar. The amount and time sequence of initial adhesion and spreading of platelets was related to the extent and time sequence of peak thrombus formation. The partially purified fibrinogen-coated and vWF-coated surfaces had more adhered and spread platelets at the earliest time points and a greater number of larger thrombi at the peak deposition times. The slowest rate of platelet adhesion and spreading was seen on the purified fibrinogen-coated surface. White blood cells were present very early on surfaces precoated with vWF and partially purified fibrinogen, and were present prior to embolization on all surfaces. Major conclusions from this work indicate that, although fibrinogen and fibronectin promote thrombogenesis when adsorbed to a surface, vWF is even more active in promoting platelet deposition and in anchoring thrombi to the surface of biomaterials. Thus, differences in vWF adsorption to biomaterials may be a determinant of surface-induced thrombogenesis.

Blood Compatibility of Polyethylene and Oxidized Polyethylene in a Canine A-V Series Shunt:Relationship to Surface Properties

The contact of blood with a polymer surface results in the initial deposition of proteins, platelets, and other formed elements. Proteins deposit during the first moments of blood contact1, while platelets start to adhere after about one minute of blood contact, when the protein layer is about 200 A thick2. The polymerization of fibrinogen to fibrin, and the activation and aggregation of platelets, lead to thrombus formation and growth on the artificial surface.