In a newly developed ex vivo model, nonanticoagulated blood was drawn from the antecubital veins of 10 healthy donors with a 19-gauge needle. A 60-cm vascular graft with a diameter of 3 mm was directly connected to the needle (Fig 1). During 6 minutes, the blood was aspirated with a constant flow rate of 20 mL/min by using a syringe pump (Harvard Apparatus, South Natick, Mass). This flow rate and graft diameter result in a shear rate of 74/s, which reflects venous flow conditions and favors fibrin-rich clot formation. A cuff was wrapped around the upper arm to ensure a constant pressure of 45 mm Hg, resulting in a continuous blood flow through the graft during the experiment. Volunteers denied taking any medication 2 weeks before the experiment and gave informed consent.