Platelet adhesion on immobilized collagen matrix under arterial shear is restricted by Shh antagonists. Washed human or murine platelets were perfused over an immobilized collagen matrix for 5 minutes in a microfluidic flow chamber at a shear rate of 1500s⁻¹. (A,C,E,G) Representative images of platelet accumulation after 5 minutes of perfusion of human (A,C) or murine (E,G) platelets. Total thrombi area after 5 minutes of perfusion of human (B,D) or murine (F,H) platelets calculated as the average surface area covered by platelets in 5 representative fields. Figures are representative of ≥3 individual experiments (mean ± standard error of the mean). *P < .05 as compared with vehicle-treated control platelets.