Fig. 5

Critical shear rate of rolling aggregate formation depends on mobile VWF fraction. After biofunctionalisation with wt VWF, channels are perfused with whole blood supplemented with indicated mobile VWF variant and observed using RICM. The critical shear rate for VWF-platelet aggregate formation is analysed by consecutively increasing the shear from 1000 s^− 1 to 5000 s^− 1 in steps of 500 s^− 1 (a) Whereas the VWF A1-domain deletion completely fails to induce rolling aggregates, del-A2 shows a gain of function by decreasing the critical shear compared to wt VWF; del-A3 does not influence the critical shear rate. Red-arrowed circles illustrate aggregates rolling on the surface in the marked direction. In the right column, magnifications of rolling aggregate regions at the critical shear rate are depicted if available. Scale bars correspond to 50 μm. (b) The RICM signal intensities (MI [AU]) for wt VWF (black line), del-A1 (green line), del-A2 (red line) and del-A3 (grey line) of the VWF-platelet aggregates are plotted against the time, representing distinct shear rates as indicated. Maximum fluctuations in the intensity plots correspond to the critical shear rate ɣ_crit. The analysed ɣ_crit for del-A2 VWF is about 40% less than for wt VWF. Note that the detection of fluctuations as transition point representing ɣ_crit has two consequences: 1. The plotted intensities have to be representative tracings out of four independent experiments for each group as a graphical overlay would naturally mask this transition point. 2. With the discrete step width of 500 s^− 1 the single experiments of each experimental group showed exactly the same depicted transition point. Therefore, ɣ_crit for del-A2 is significantly lower than ɣ_crit for wt VWF and del-A3 VWF. While the certainty is predominantly determined by the step width, we avoid indicating a P value