Inertial migration of erythrocytes in low-viscosity and high-shear rate microtube flows: Application of simple digital in-line holographic microscopy

A simple digital in-line holographic microscopy technique is applied to investigate the inertial migration of human erythrocytes in low-viscosity and high-shear rate microtube flows. The technique provides radial distribution statistics of the erythrocytes, as well as their orientation information in the tube flow. The radial distribution of human erythrocytes is found to be similar to that of spherical particles of 7 μm in diameter. The results show that both the erythrocytes and the spherical particles are fully focused at similar radial positions as the shear-rate of the flow increases. The erythrocytes require a higher shear rate than the spherical particle to establish the fully focused state. As the radial migration of erythrocytes fully develops, more than half of the cells have symmetry axes orthogonal to the main stream and wall-normal directions. This orientation demonstrates similar hydrodynamic effects of disk-shaped biconcave erythrocytes to those of the spherical particles, and consequently results in similar radial equilibrium positions.