Kinetics of Platelet Adhesion to Artificial Surfaces in Vitro

Adhesion of platelets to glass, collagen-coated glass, albumin-coated glass, polystyrene, sulfonated polystyrene and a segmented polyurethane, has been studied in vitro. The apparatus is of the Couette flow type and allows close control of fluid shear and diffusional factors. Suspensions of washed pig platelets constitute the basic platelet medium. This can be modified by adding back red cells and specific plasma proteins in varying concentration and the platelet concentration can be varied without compromising viability. Adhesion is measured by radiolabelling methods.

In the absence of red cells, low levels of adhesion were seen on all surfaces with saturation occurring at 4 to 6 platelets/1000 μ² in 2 to 4 minutes. In the presence of red cells adhesion was much greater. Collagen was the most reactive surface and adhesion data was consistent with a platelet diffusivity 10 to 100 times that predicted by Brownian motion. The diffusivity was dependent on shear rate and hematocrit. All other surfaces showed a 2-fold increase in adhesion compared to the values without red cells. However adhesion was independent of hematocrit above 10% and reached a constant value of about 12 (less for albumin monolayer) in 2 to 10 minutes.