Fibrinogen and von Willebrand's factor adsorption are both required for platelet adhesion from sheared suspensions to polyethylene preadsorbed with blood plasma

Previous studies showed that platelet adhesion to biomaterials from static suspensions was greatly increased by the adsorption of even very small amounts (<5 ng/cm2) of fibrinogen (Fg). In this study, the sensitivity of platelet adhesion to Fg was reexamined by measuring platelet adhesion under flow conditions. The role of adsorbed von Willebrand's factor (vWf) was also studied. Polyethylene (PE) tubing was preadsorbed with Fg, vWf, vWf-deficient plasma, and Fg-deficient plasma or serum with added Fg, and Fg adsorption measured with 125I Fg. Platelets in a red blood cell suspension were passed through the tubes at either low (50 s(-1)) or high (500 or 1000 s(-1)) shear rates and adhesion measured with an improved LDH assay. Adhesion from flowing suspensions measured after preadsorption with afibrinogenemic plasma or serum was very low, but increased greatly with addition of Fg. Less than 10 ng/cm2 of adsorbed Fg was enough to greatly enhance platelet adhesion. Adhesion at high shear was also strongly affected by vWf, as platelet adhesion at 500 s(-1) to PE preadsorbed with vWf-deficient plasma decreased by more than tenfold compared to adhesion at 50 s(-1), but platelet adhesion to PE preadsorbed with normal plasma increased about eightfold when shear rate was increased. The results show that very low amounts of adsorbed Fg are able to support platelet adhesion under shear flow. However, adsorbed vWf also appears to play an important cofactor role in platelet adhesion to biomaterials, as its presence greatly augments platelet adhesion under high shear.