3D Particle Tracking Velocimetry applied to platelet-size particles in red blood cells suspensions flows through square microchannels

General defocusing particle tracking (GDPT) method is used to characterize the motion of platelet-size particles within red blood cell (RBC) suspension flows through straight-square microchannels. The method is able to characterize the
three-dimensional (3D) nature of particle-RBC interactions, however the measurement depth is limited by the height of the microchannel and hematocrit level (Hct). The RBC mask the particle images and detection becomes impossible above a limit depth. The pressure-driven flow is characterized by velocity distributions and 3D trajectories of platelet-size particles within the RBC suspensions. At large hematocrit levels (Hct=30 %), the velocity distribution exhibits a blunter profile typical of blood flow in capillary-size microchannels. In addition, the interplay between blood viscosity and pressure-driven flow causes the velocity magnitude to decrease, in the center region, with increasing hematocrit. The platelet-size particles exhibit larger velocity fluctuations along the spanwise and vertical directions as Hct is increased, both inside the RBC-rich region and cell-free layer (CFL). On one hand, inside the RBC-rich zone the increasing number of flowing RBC leads to more frequent particle-RBC collisions. On the other hand, even though the particle movement inside the CFL is confined between the boundary of the RBC and the wall of the microchannel, as the thickness of the CFL decreases (i.e. increasing Hct) the collisions with RBC become more frequent. To the authors knowledge, these results represent the first experimental characterization of 3D platelet-size particle behaviour and near-wall dynamics within RBC-suspensions, and it paves the way for more detailed particle-cell flows characterization.