Fig. 4

Threshold extensional strain triggers platelet [Ca²⁺]_c flux independent of wall shear stress. A CFD-derived extensional strain rate profile at hyperbolic centerline for Q = 12.5, 50, 200, and 600 μL/min. Grey region defines the hyperbolic phase. B CFD-derived rate of change in extensional strain rate profile at hyperbolic centerline. Inset—zoomed view of hyperbolic entry. Grey region defines the hyperbolic phase. C Human platelet [Ca²⁺]_c as a function of Q. Dotted line represents baseline [Ca²⁺]_c cutoff = 75 nM. Solid lines are a rolling average (2nd-order smoothing—10 neighbors). Grey region defines the hyperbolic phase. Note that Ca²⁺ activation is on/off such that it initiates at the beginning of the Hyperbolic zone (constant \(\dot{\varepsilon}\)) and immediately “shuts off” upon ejection into the Downstream expansion zone (\(\dot{\varepsilon}\) = 0). D Frequency histogram showing the distribution of platelet [Ca²⁺]_c (10 nM bins) within the first 100 μm of Hyperbolic flow as a function of applied \(\dot{\varepsilon}\). Q = 12.5 μL/min (N = 3 experiments); Q = 50 μL/min (N = 3 experiments); Q = 200mL/min (N = 4 experiments); Q = 600 μL/min (N = 4 experiments). Dotted line represents baseline [Ca²⁺]_c cutoff = 75 nM. E Platelet [Ca²⁺]_c as a function of applied extensional stress (Pa) at maximum \(d\varepsilon \left/ d x\right.\) for Q = 12.5, 50, 200, and 600 μL/min. Dotted line represents baseline [Ca²⁺]_c cutoff = 75 nM. [Agonist] vs. response Variable slope (four parameters) Least squares fit + 95% CI shown of N = 4 independent experiments. Note that maximal [Ca²⁺]_c at σ = 43.3 Pa ranges between ~220 and ~600 nM.