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A method to produce a hydrogel by covalently coupling dextran polysaccharide to silicon and silicon rubber surfaces is described. A bifunctional epoxysilane was used as coupling mediator and the conditions for the reaction were optimized. Coupling of the silane to silicon rubber was possible only after oxidation of the surface by plasma etching. The reaction between the epoxy-group and dextran was concentration dependent and required high concentrations of dextran. The turnover rate of fibrinogen in solution at the hydrophilic surface was found to be high when measured by ellipsometry.

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A procedure is presented allowing detailed studies of the adsorption of coagulation factors from whole blood on to surface. Anticoagulant (citrate or hirudin) was added to fresh venous blood. The blood was incubated in hydrophilic or hydrophobic glass tubes without contact with air. The adsorption of fibrinogen, fibronectin and factor IX was measured with an enzyme immunoassay using specific antibodies directed against these proteins. Adsorption of enzymically active kallikrein was measured using a chromogenic peptide substrate. Adhesion and activation of platelets was measured by direct examination in a scanning electron microscope and by measurement of release of beta-thromboglobulin. The results show that the adsorption of plasma proteins at the blood-solid interface is dependent on the anticoagulant used, surface energy of the test surface and incubation time. In experiments using hirudin a specific inactivator of thrombin, as anticoagulant, we found dynamic changes of the adsorbed protein film which could not be studied using citrated blood.

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