Concentration of Annexin V, FX, and FXa on the “caps” in thrombi and its possible significance. (A) Typical epifluorescence microscopy images of platelet aggregates formed after perfusion of hirudinated human whole blood over immobilized collagen at 1000 s−1 (1500 s−1 for FX/FXa) for 5 minutes. Platelet aggregates were visualized using DIC and epifluorescent microscopy (×63 objective). Representative images of DIC and FITC (green) fluorescence of Annexin V, FX, or FXa are shown. Red arrows indicate typical PS-positive platelets with “caps.” Scale bar, 25 μm. (B) Design of a CFD model to evaluate blood flow within and outside of a “cap.” Hemispheric thrombus and procoagulant platelet at its surface are shown in blue. Flow direction is shown with white arrow. (C) Shear rates color map derived from CFD simulation for the central vertical cross-section of the vessel. Maximum shear rate is observed at the top of the “balloon” body of a procoagulant platelet, whereas the minimum values are inside the “cap” (indicated with a yellow arrow).
