Organization and dynamics of red blood cells in a stenosed microchannel under time-dependent flow

The circulatory system is a complex vessel network that distributes blood to body tissues and organs. In the microcirculation, red blood cells (RBCs) tend to migrate away from the vessel walls, thus forming a core RBC flow and a cell-free layer (CFL) that determines the unique flow properties of blood. Constricted vessels, such as stenosed arteries, can dramatically affect RBC distribution and CFL development.

This study investigates RBC organization and CFL dynamics under time-dependent flow. We use a high-precision pressure device to pump RBC suspensions with concentrations ranging from 1% to 20% in volume through a microfluidic constriction. We employ a sinusoidal pressure modulation to examine the time-dependent CFL and perform high-speed optical microscopy at various positions before and after the constriction. The resulting image sequences are synchronized with the phase of the driving and post-processed with a customized routine that allows us to determine the RBC core flow even at low concentrations and under time-dependent flow conditions. Our results highlight the dominant effects of the RBC concentration and the amplitude of the applied pressure signal on the CFL dynamics. Complementary numerical simulations reveal how the time-dependent CFL is coupled with the dynamically changing flow field at the constriction. Our study provides crucial insight into the flow behavior of complex fluids in unsteady microscale flows.