Integrated system investigating shear-mediated platelet interactions with von Willebrand factor using microliters of whole blood

We report an integrated platelet translocation analysis system that measures complex dynamic platelet-protein surface interactions in microliter volumes of unmodified anticoagulated whole blood under controlled fluid shear conditions. The integrated system combines customized platelet-tracking image analysis with a custom-designed microfluidic parallel plate flow chamber and defined von Willebrand factor surfaces to assess platelet trajectories. Using a position-based probability function that accounts for image noise and preference for downstream movement, outputs include instantaneous and mean platelet velocities, periods of motion and stasis, and bond dissociation kinetics. Whole blood flow data from healthy donors at an arterial shear rate (1500 s(-1)) show mean platelet velocities from 8.9+/-1.0 to 12+/-4 microm s(-1). Platelets in blood treated with the antiplatelet agent c7E-Fab fragment spend more than twice as much time in motion as platelets from untreated control blood; the bond dissociation rate constant (k(off)) increases 1.3-fold, whereas mean translocation velocities do not differ. Blood from healthy unmedicated donors was used to assess flow assay reproducibility, donor variability, and the effects of antiplatelet treatment. This integrated system enables reliable, rapid populational quantification of platelet translocation under pathophysiological vascular fluid shear using as little as 150 microl of blood.