The contact of flowing blood with an artificial surface leads to adsorption of plasma proteins, followed by platelet adhesion and aggregation and thrombus formation. This phenomenon is enhanced by turbulent flow at joints, bifurcations, and constrictions. In therapeutic plasmapheresis using an IBM blood cell separator, blockage of the extracorporeal circulation system by platelet-fibrin thrombi imposed a halt in treatment for manual clearance of the circuit for 66 in 149 cases (44%). Thus it was decided to passivate the surface of the extracorporeal circuit by filling the tubing with 4% human serum albumin 15-20 min before the treatment session and then displacing the albumin solution with the patient's blood without creating an air-liquid interface. After introduction of this technique, a blockage was observed for only 11 in 239 cases (5%). In vitro measurements of platelet accumulation on the internal surface of the circulation system were carried out using washed human platelets labeled with 111In-oxine in the presence of a 40% hematocrit. Preadsorption of the surface with albumin reduced platelet deposition to 4-5% that observed for an equivalent pretreatment with physiological saline.

The synthesis of a triblock copolymer poly-(N-acetylethyleneimine)-polyethylenoxide-poly(N-acet ylethyleneimine) includes two successive steps: the first is the functionalization of a poly(ethyleneglycol) precursor by creating sulfonic esters at its chain ends, the second uses these esters to initiate the cationic polymerization of 2-methyl-2-oxazoline. Homopolymers appear in the raw product; hence successive selective extractions of the copolymer with benzene and dioxane are necessary. The final yield in pure copolymer was 11%. The copolymer was characterized by UV and 1H-NMR spectrometry and light scattering. Adsorption isotherms were determined on silica, for varying pH and salt concentration. Optimum conditions for coating silica with the polymer were determined. The efficiency of this precoating to reduce the adsorption of fibrinogen was very high (99.2% reduction with respect to bare silica). Steric exclusion chromatography of a variety of proteins gave a satisfactory calibration curve. Platelet accumulation on copolymer precoated glass was reduced to 10-20% of its value on bare glass, a result superior to that obtained by albumin passivation of the same glass surface.

SummaryA rat thrombosis model was developed to assess the efficacity of antithrombotic drugs. It had the following characteristics: controlled hemodynamic and rheological conditions corresponding to arterial flow, a collagen coated surface as a relevant thrombogenic stimulus, a method of measurement allowing dynamic monitoring of thrombus formation and the possibility to assess the thrombus structure. A shunt composed of polyethylene and silicone catheters, including in the middle of the shunt a collagen coated glass capillary, was inserted between the two primitive carotids of the rat. The duration of patency of the shunt was recorded using a thermic probe fixed on its central part. In this model, the patency of the shunt was 539 ± 55 s. Platelet and fibrinogen-fibrin accumulation in successive one centimeter segments along the shunt were measured using 111In labeled platelets and 125I labeled fibrinogen. Platelet accumulation occurred on the collagen coated surface and at the junctions between the different components of the shunt, where flow was disturbed. The effects of four antithrombotic agents were measured: aspirin, clopidogrel, heparin and r-hirudin. Clopidogrel, heparin and hirudin significantly prolonged patency duration of the shunt, whereas aspirin was inactive. Aspirin did not reduce platelet or fibrinogen-fibrin accumulation on the collagen coated surface. Platelet accumulation on the collagen surface was significantly lower in the clopidogrel group (50 mg/kg) than in the group treated with heparin (500 U/kg), demonstrating the direct antiplatelet effect of clopidogrel. Hirudin at doses giving similar values of APTT as heparin (500 U/kg) prolonged the occlusion time to over 2 h while the heparin occlusion time was only 20 min. We conclude that this experimental arterioarterial thrombosis model is sensitive to both antiplatelet and anticoagulant agents, allowing discrimination between antiplatelet and anticoagulant mechanisms of thrombosis prevention. The technique is easily performed in a small animal, fast and reproducible, and thus comparable to primate models for use in the screening of new antithrombotic drugs.

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