Abstract
Knowledge about the flow field of the plasma around the red blood cells in capillary flow is important for a physical understanding of blood flow and the transport of micro- and nanoparticles and molecules in the flowing plasma. We conducted an experimental study on the flow field around red blood cells in capillary flow that is complemented by simulations of vortical flow between red blood cells. Red blood cells were injected in a 10×12µm rectangular microchannel at a low hematocrit, and the flow field around one or two cells was captured by a high-speed camera that tracked 250nm nanoparticles in the flow field, acting as tracers. While the flow field around a steady "croissant" shape is found to be similar to that of a rigid sphere, the flow field around a "slipper" shape exhibits a small vortex at the rear of the red blood cell. Even more pronounced are vortex-like structures observed in the central region between two neighboring croissants. The rotation frequency of the vortices is to a good approximation, inversely proportional to the distance between the cells. Our experimental data are complemented by numerical simulations.
Highlights
Blood flow in microcapillaries is a prime example of a biological fluid-structure interaction problem between the elastic red blood cells (RBCs) and the hydrodynamic flow of plasma.1–3 Over recent years, quite some attention has been paid to the dynamics of RBCs in cylindrical or rectangular channels, which are known to be the most common configurations in model microfluidic flows
Some works reported on observations of clusters of two or more RBCs formed without any molecular interactions that can be induced by the plasma molecules but kept together with a certain distance of a few microns in-between the cells by Abbreviations: BI, boundary integral; BSA, bovine serum albumin; phosphate-buffered saline (PBS), phosphate buffer saline; PDMS, polydimethylsiloxane; PTV, particle tracking velocimetry; RBCs, red blood cells
| 2 of 8 hydrodynamic interactions.19–26 While there is good agreement between numerical simulations and experiments regarding the actual shape of RBCs, less attention has been paid to resolve the flow field of the surrounding plasma experimentally
Summary
Blood flow in microcapillaries is a prime example of a biological fluid-structure interaction problem between the elastic red blood cells (RBCs) and the hydrodynamic flow of plasma.1–3 Over recent years, quite some attention has been paid to the dynamics of RBCs in cylindrical or rectangular channels, which are known to be the most common configurations in model microfluidic flows. | 2 of 8 hydrodynamic interactions.19–26 While there is good agreement between numerical simulations and experiments regarding the actual shape of RBCs, less attention has been paid to resolve the flow field of the surrounding plasma experimentally. For a simple sphere in a cylindrical channel, the flow pattern can be computed analytically, but results in surprisingly intricate dynamics of the solute.[36] While there is quite some literature on the flow field in microchannels around rigid or only slightly deformable objects such as microspheres or droplets,37–40 experimental data are rare for the complex flows arising due to the above-described croissant and slipper motions of red blood cells. During the observation time span, the distance dRBC between two consecutive RBCs never changed more than 10% in our experiments; that is, both cells had comparable velocities
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