Erythrocyte Concentration Distribution in Sheathed Microfluidic Flows

Abstract

The combined effect of dissociative and associative forces on erythrocytes flowing in direct, layered contact with cell-free "sheath" flows in microfluidic systems was studied to aid in the design of blood purification devices. A blood stream flowed in direct contact between two fluids that were cell free. The layered flow created a sharp transverse concentration gradient of erythrocytes that promoted lateral movement of cells. This movement was perceived as both dispersive (arising from particle collisions or shear-enhanced movement) and associative (arising from rouleau formation and shear-induced migration, which limited the extent of movement and maintained a higher hematocrit in the central layer). The concentration changes of erythrocytes in the blood and sheath streams were measured to determine the flux of cells between streams. At flows with low wall shear rates, the flux of erythrocytes into the sheath streams was small. When shear was increased, cell flux away from the central layer increased. There was an intermediate shear rate that maximized cellular flux away from the center stream, and a further increase in shear rate showed no change in cell flux. Changing the transverse position of erythrocytes entering the system strongly affects their distribution in the exiting stream even for long fluid residence times. The results clarify microfluidic device design and elucidate how shear and hematocrit affect erythrocyte movement in blood.