Formation of membrane tethers in vitro. Washed platelets (150 × 10⁶/mL) reconstituted with RBCs were perfused through microcapillary tubes coated with VWF (10 μg/mL) at 1800 s⁻¹. (A) DIC image and (B) SEM image of a single platelet forming membrane tethers with immobilized VWF. (C) SEM image of a forming discoid platelet aggregate. This image demonstrates that the adhesion contacts between aggregating platelets are mediated by membrane tethers. Platelets were fixed at 120 seconds and processed for SEM imaging as described in “Scanning electron microscopy.” Scale bar = 2 μm.