Figure 1
From: Margination and stretching of von Willebrand factor in the blood stream enable adhesion
Simulation and experimental measurements. (a) Snapshots from 2D and 3D simulations with RBCs colored in red and VWFs in green. The simulation setup corresponds to a cylindrical microvessel in 3D with the diameter W = 20 μm or to a channel in 2D with the width W = 20 μm. (b) Experimental setup consists of a microfluidic system with multiple identical channels (two channels are shown). At the pre-processing step, channel walls are coated with collagen. Blood with different H t levels is perfused through the device (from an inlet on the right to an outlet on the left) using a pneumatic pump. Optical microscopy is performed in the middle of the wide-channel section marked by the small oval area, where we can observe RBCs but not VWF because it needs to be detected by fluorescence microscopy. (c) Simulation measurements supply distributions of different components in blood flow. The plot shows a comparison of center-of-mass (COM) distributions of RBCs and VWFs obtained from a 2D simulation with H t = 0.6 and a 3D simulation with H t = 0.4 for a nearly same thickness of RBC-FL and a pseudo-shear rate of \({\dot{\gamma }}^{\ast }\approx 60\) (\(\bar{\dot{\gamma }}\approx 62\) s−1). The distributions from 2D and 3D simulations compare well for a fixed thickness of the RBC-FL, indicating that hematocrit values in 2D correspond to lower hematocrits in 3D. The inset presents the RBC-FL thicknesses δCFL for different H t and demonstrates that a negative shift by about 0.15–0.2 is required to relate H t in 2D to that in 3D. (d) Experimental measurements provide fluorescence intensity of labelled VWFs near the channel bottom. The isotropic background level of measured intensity (I x) characterizes the amount of flowing VWF near the wall (or VWF margination), while the bright spots correspond to adhered VWF molecules or aggregates. The intensity in the right plot for H t = 0.5 is clearly stronger than on the left for H t = 0.1 indicating that VWF margination is more pronounced at H t = 0.5. All measured intensities are normalized by the wall autofluorescence intensity I w (the black marked area), which remains constant throughout all performed experiments. Scale bars correspond to 50 μm.
