Margination of platelet-sized particles in red blood cell suspensions near the confluence and bifurcation of Y-shaped microchannels

Platelets are known to concentrate near the vessel wall in microvascular blood flow, a phenomenon referred to as margination or near-wall excess. However, platelet margination is expected to be impaired at the confluence of two vessels or bifurcation, and to complete again at a certain distance downstream from the confluence or bifurcation. In this study, we performed in vitro experiments to investigate these margination distances, by using fluorescent polystyrene particles of similar diameter to platelets as a platelet substitute. A confocal laser scanning microscopy was used to measure the distribution of particles suspended in the red blood cell suspension flowing through Y-shaped microchannels. In confluence channels, margination was reconstructed less than 5 mm from the confluence, while in bifurcating channels, it was reconstructed approximately 30 mm from the bifurcation point. These lengths are larger than typical microvessel lengths, suggesting that complete margination is rare in microvessels. Furthermore, it is suggested that platelet margination in venules is less pronounced than in arterioles, and platelets are distributed unevenly at each branching of arterioles.