In vitro blood flow and cell-free layer in hyperbolic microchannels: Visualizations and measurements

Raquel O Rodrigues,Patrícia C Sousa,Ana I Pereira,Raquel Lopes,Valdemar Garcia,Diana Pinho,Stefan Gassmann,Rui Lima

doi:10.1007/s13206-016-0102-2

Raquel O Rodrigues, Patrícia C Sousa + Show 6 more

Open Access

https://doi.org/10.1007/s13206-016-0102-2

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Abstract

Red blood cells (RBCs) in microchannels has tendency to undergo axial migration due to the parabolic velocity profile, which results in a high shear stress around wall that forces the RBC to move towards the centre induced by the tank treading motion of the RBC membrane. As a result there is a formation of a cell free layer (CFL) with extremely low concentration of cells. Based on this phenomenon, several works have proposed microfluidic designs to separate the suspending physiological fluid from whole in vitro blood. This study aims to characterize the CFL in hyperbolic-shaped microchannels to separate RBCs from plasma. For this purpose, we have investigated the effect of hyperbolic contractions on the CFL by using not only different Hencky strains but also varying the series of contractions. The results show that the hyperbolic contractions with a Hencky strain of 3 and higher, substantially increase the CFL downstream of the contraction region in contrast with the microchannels with a Hencky strain of 2, where the effect is insignificant. Although, the highest CFL thickness occur at microchannels with a Hencky strain of 3.6 and 4.2 the experiments have also shown that cells blockage are more likely to occur at this kind of microchannels. Hence, the most appropriate hyperbolic-shaped microchannels to separate RBCs from plasma is the one with a Hencky strain of 3.

Highlights

Red blood cells (RBCs) are the most abundant kind of cells that flows within the human circulatory system
A well-known physiological phenomenon happening in microcirculation, named as the Fåhræus Lindqvist effect, is the tendency of the RBCs to migrate to the centre of the microchannel and leading to the formation of two phases, i. e., a flow core with mainly RBCs and a cell free layer (CFL)
These results show clearly that this kind of hyperbolics contractions (Hencky strain 2) does not interfere in the CFL thickness

Summary

Introduction

Red blood cells (RBCs) are the most abundant kind of cells that flows within the human circulatory system. They are responsible for the supply of oxygen and nutrients to the body and removal of carbon dioxide and metabolic wastes from tissues. Blood flow behaviour depends on several combined effects such as cell deformability, flow shear rates and geometry of the microvessel [1, 2]. A well-known physiological phenomenon happening in microcirculation, named as the Fåhræus Lindqvist effect, is the tendency of the RBCs to migrate to the centre of the microchannel and leading to the formation of two phases, i. The CFL is known to control the nitric oxide (NO)

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