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

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.

In vitro particulate analogue fluids for experimental studies of rheological and hemorheological behavior of glucose-rich RBC suspensions

“…These results corroborate qualitatively the blood flow studies performed by other authors. 8,9,12,22 The CFL thickness for the simple geometries M 1 and M T and for 20% of healthy RBCs (closer to in vivo microcirculation environments) is also in good agreement with the in vivo results of Kim et al 6 and Yamaguchi et al…”

“…Moreover, at these small dimensions, the elasticity of the fluid can be assessed while limiting inertial effects. The microchannel M T has an abrupt contraction followed by a smooth triangular expansion and also has a high Henchy strain of 3 promoting the CFL formation downstream of the contraction, and as Rodrigues et al 9 conclude in their study, e H ! 3 has a strong impact on the CFL thickness.…”

“…9 Similar measurements were also carried out for the analogue fluid, i.e., PMMA microbeads at 1% (w/w) suspended in the viscoelastic base fluid. These latter results were compared with data obtained from the healthy and glucose-rich RBCs deformability tests.…”

“…The orientation of the RBCs at high shear rates and their tendency to migrate to the center line of the microchannels (in vitro) [1][2][3] or microvessels (in vivo) 4,5 originate the formation of a cell depleted layer near the walls, known as the cell-free layer (CFL). The CFL is influenced by the formation of aggregates, cell interactions and deformability, hematocrit, flow rate, viscosity, and geometry 6,7 and is a microscopic level phenomenon that occurs in microfluidic devices 2,6,8,9 and in microvessels [10][11][12] with dimensions in the range of 300 lm down to 10 lm. Several studies have been performed both in vivo 11,13,14 and in vitro 2,9,[15][16][17][18] to better understand the CFL formation, which influences its thickness and the advantages and disadvantages of the presence of this layer in the human microcirculatory system 6 and in microchannels.…”

“…The CFL is influenced by the formation of aggregates, cell interactions and deformability, hematocrit, flow rate, viscosity, and geometry 6,7 and is a microscopic level phenomenon that occurs in microfluidic devices 2,6,8,9 and in microvessels [10][11][12] with dimensions in the range of 300 lm down to 10 lm. Several studies have been performed both in vivo 11,13,14 and in vitro 2,9,[15][16][17][18] to better understand the CFL formation, which influences its thickness and the advantages and disadvantages of the presence of this layer in the human microcirculatory system 6 and in microchannels. 8,16,19 It is also important to refer that in real blood, there is a migration of white blood cells from the core towards the wall region of the vessels, a phenomenon called margination, 20,21 but this issue is outside the scope of this work.…”