Margination of platelet-sized particles in normal and hardened red blood cell suspension flows

It has been known that platelets in microvessels have enhanced concentrations near the vessel wall (near-wall excess, NWE). Existing studies showed that this phenomenon does not occur in the absence of red blood cells (RBCs), which indicates the essential role of RBCs in NWE. In the present study, we examined the effect of RBC deformability on NWE, by adopting platelet-sized fluorescent particles for platelet substitutes to measure the cross-sectional distributions of particles mixed in normal or hardened RBC suspensions flowing through microchannels. The fluorescence observation was performed over the cross section of circular or rectangular channels with use of a confocal laser scanning microscope system. It was found that in rectangular channels, platelet-sized particles mixed in normal RBC suspensions were concentrated near four corners in the cross section, while in circular channels they were concentrated along the circumference of the channel wall. For particles mixed in highly hardened RBC suspensions, NWE was scarcely observed in both channels. These results suggest that NWE of platelets can be attributed to high deformability of RBCs, which induces their axial accumulation. The interaction with such RBCs expels platelets into the marginal layer near the channel wall.