Activity of ADAMTS13, MDTCS, and T4L/T8L-ADAMTS13 in a microfluidic flow assay. DiOC6-stained platelets were perfused over a microfluidic flow chamber lined with histamine-stimulated HUVECs, forming stable VWF-platelet strings. Channels were then perfused with 5 mL of 5 nM MDTCS, 5 nM WT-ADAMTS13, 5 nM T4L/T8L-ADAMTS13, or ADAMTS13 reaction buffer (n = 3). Using a Leica Stellaris 5 inverted confocal microscope (10× dry lens; λ_ex = 490 nm; λ_em = 525 nm), videos were captured at 0.77 frames per second; (A) photographic representation of experimental replicate. Experiments occurred at room temperature. The total length of strings within the frame was quantified every 20 frames for 5 frames. Rates were determined using linear regression (B), and differences between rates were assessed using unpaired t tests (Table 2). Error bars represent standard deviation, and symbols represent 4 experimental conditions: buffer (▲), MDTCS (■), WT-ADAMTS13 (●), T4L/T8L-ADAMTS13 (▼). ∗P < .05, vs MDTCS.