VWFpp inhibits thrombus formation on collagen surfaces. 2′,7′-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein–labeled whole blood was perfused at 3000 s⁻¹ over collagen substrate in the presence of anti-VWF mAbs (SZ-123 and DD3.1) or 5-50 μg/mL of VWFpp. PPACK was used as an anticoagulant. (A) The percent surface area covered with immobilized platelets was quantified. Onset of thrombus formation in the presence of VWFpp was delayed at 2 minutes (*P < .05). (B) Snapshot of the collagen substrate at 2 minutes under the specified conditions.