The influence of red blood cell deformability on hematocrit profiles and platelet margination

The influence of red blood cell (RBC) deformability in whole blood on platelet margination is investigated using confocal microscopy measurements of flowing human blood and cell resolved blood flow simulations. Fluorescent platelet concentrations at the wall of a glass chamber are measured using confocal microscopy with flowing human blood containing varying healthy-to-stiff RBC fractions. A decrease is observed in the fluorescent platelet signal at the wall due to the increase of stiffened RBCs in flow, suggesting a decrease of platelet margination due to an increased fraction of stiffened RBCs present in the flow. In order to resolve the influence of stiffened RBCs on platelet concentration at the channel wall, cell-pair and bulk flow simulations are performed. For homogeneous collisions between RBC pairs, a decrease in final displacement after a collision with increasing membrane stiffness is observed. In heterogeneous collisions between healthy and stiff RBC pairs, it is found that the stiffened RBC is displaced most. The influence of RBC deformability on collisions between RBCs and platelets was found to be negligible due to their size and mass difference. For a straight vessel geometry with varying healthy-to-stiff RBC ratios, a decrease was observed in the red blood cell-free layer and platelet margination due to an increase in stiffened RBCs present in flow. Author summary The primary function of the human red blood cell is to deliver oxygen to the tissues of the body. The ability of the red blood cell to deform allows it to squeeze through small capillaries along with helping transport platelets to damaged areas on the vessel wall, which initiates normal coagulation function. Many diseases are known to impede the deformability of the red blood cell, which may adversely impact the transport of red blood cells and platelets in flow. We observe that with increasing fractions of stiff red blood cells in flow, there is a decrease of platelet margination. Specifically, this is observed as a decrease of the fluorescent platelet signal at the wall of a glass channel with flowing whole blood. We confirm this margination decrease by performing cell resolved simulations that reproduce the experiments. We also observe, in simulation, a decrease in the red blood cell-free layer as red blood cell deformability decreases. The decrease in the cell-free layer, we believe, is the most significant contributing factor to decreased margination.