Microfluidics thrombus formation assay. (A-C) Washed blood containing fluorescent-labeled platelets and 10 µg/mL WT-VWF/Lock-VWF were perfused at a wall shear rate of 500/s over substrates adsorbed with 40 µg/mL ΔA1-VWF. (A) Thrombus formation was measured based on fluorescence intensity in the field of view. (B) Representative images of platelet accumulation on ΔA1-VWF substrate shows greater accumulation in the case of WT-VWF. (C) Platelet accumulation on ΔA1-VWF in runs containing WT-VWF was blocked by mAbs against GpIbα (AK2), VWF-A1 (AVW-3) and VWF-D’D3 (clone DD3.1). (D-E) Thrombus formation on collagen substrate in the presence of 10 µg/mL WT-VWF or Lock-VWF. (D) Wall shear rate was varied: 400/s, 1000/s, and 2000/s. Thrombus formation was blocked by mAbs AK2, AVW-3, and DD3.1, at 1000/s. (E) Representative images of thrombus formation at 3 minutes at different shears. All microfluidics assays were performed 3 to 4 times, each with 2 to 4 repeats. *P < .05 with respect to all other treatments. (B,E) Scale bars, 100 µm. Platelets stained using BCECF-AM.