Development of margination of platelet-sized particles suspended in red blood cell suspension flows through Y-shaped bifurcating microchannels

Background In the blood flow through microvessels, platelets exhibit enhanced concentrations in the layer free of red blood cells (cell-free layer) adjacent to the vessel wall. The motion of platelets in the cell-free layer plays an essential role in their interaction with the vessel wall, and hence it affects their functions of hemostasis and thrombosis. Objective We aimed at estimating the diffusivity of platelet-sized particles in the transverse direction (the direction of vorticity) across the channel width in the cell-free layer, by in vitro experiments for the microchannel flow of red blood cell (RBC) suspensions containing platelet-sized particles. Methods Fluorescence microscope observation was performed to measure the transverse distribution of spherical particles immersed in RBC suspension flows through a Y-shaped bifurcating microchannel. We examined the development of the particle concentration profiles along the flow direction in the daughter channels, starting from asymmetric distributions with low concentrations on the inner side of the bifurcation at the inlet of the daughter channels. Results In the daughter channels of 40 μm width, the reconstruction of the particle margination to achieve a symmetric concentration profile was completed in ∼30 mm from the bifurcation, independent of flow rate. Conclusions We presented experimental evidence of particle margination developing in the bifurcating flow channel, and the diffusivity of 2.9-μm diameter particles was estimated to be ∼40 μm2/s at the shear rate of 1000 s-1 and hematocrit of 0.2.