1. Consider red or white blood cell moving in a capillary that is so narrow that
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Question
1. Consider red or white blood cell moving in a capillary that is so narrow that the cells must travel in single file. A blood cell that approaches a divergent capillary bifurcation enters into the daughter channel with the faster flow rate. Explain this observation based on the fluid stresses acting on the plasma membrane of a cell that has just arrived at the flow separation point in the bifurcation. Make use of this result to design a microfluidic device (a system of microchannels that have dimensions in the micrometer range comparable to capillary diameter) that permits the effective separation of blood cells from the plasma during entry of a single droplet of blood? Such a separation device can be used to perform analysis or diagnosis of blood plasma.Explanation / Answer
WBC (White blood cells) can freely pass through the walls of a capillary and RBC (Red blood cells) travel in single file through and empty into veins. Function of red blood cells is to transport oxygen to different parts of the body. They (RBCs) flow through a symmetric micro-vascular bifurcation model, have been simulated with the 2D immersed-boundary lattice-Boltzmann method.
Flow and pressure fields in the bifurcation region indicates that the difference in flow pressure across the 2 ends of a flowing RBC is the big driving force for motion; while shear stress on back of a cell is responsible for the cells slow slide into vessel branch. The separating surface or separating location reported in many studies, where blood was treated as a continuum fluid or isolated RBCs were simulated, is not sufficient to describe individual cell motions in multiple RBC flows. This is helpful in understanding the complex phase separation process and could be useful for relevant biomedical applications.
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