Abstract
The dynamics and deformation of red blood cells (RBCs) in microcirculation affect the flow resistance and transport properties of whole blood. One of the key properties that can alter RBC dynamics in flow is the contrast λ (or ratio) of viscosities between RBC cytosol and blood plasma. Here, we study the dependence of RBC shape and dynamics on the viscosity contrast in tube flow, using mesoscopic hydrodynamics simulations. State diagrams of different RBC dynamical states, including tumbling cells, parachutes, and tank-treading slippers, are constructed for various viscosity contrasts and wide ranges of flow rates and tube diameters (or RBC confinements). Despite similarities in the classification of RBC behavior for different viscosity contrasts, there are notable differences in the corresponding state diagrams. In particular, the region of parachutes is significantly larger for λ = 1 in comparison to λ = 5. Furthermore, the viscosity contrast strongly affects the tumbling-to-slipper transition, thus modifying the regions of occurrence of these states as a function of flow rate and RBC confinement. Also, an increase in cytosol viscosity leads to a reduction in membrane tension induced by flow stresses. Physical mechanisms that determine these differences in RBC dynamical states as a function of λ are discussed.
Highlights
Microvascular blood flow is essential for the homeostasis of organism tissues, as it transports nutrients and waste products and mediates various physiological processes
Parachute is a stable stomatocyte-like red blood cells (RBCs) deformation in the tube center. These dynamical states depend on RBC mechanical properties, cell confinement, and the flow rate
We primarily focus on how the viscosity contrast affects these dynamical states for a wide range of RBC confinements and flow rates
Summary
Microvascular blood flow is essential for the homeostasis of organism tissues, as it transports nutrients and waste products and mediates various physiological processes. In addition to the parachute and slipper shapes, snaking dynamics (a periodic cell swinging around the tube center) at low flow rates and a region of coexisting parachutes and slippers at high flow rates were reported [24, 25] These 2D simulations have demonstrated that the transition between parachute and slipper shapes can be triggered by changes in flow rate or RBC membrane elasticity. This transition can be characterized by the distance between the cell’s center-of-mass and the channel center, which has been shown to have a similar behavior as a pitchfork bifurcation [23]. Several state diagrams of RBC dynamics, including snaking, tumbling, tank-treading slipper, and parachute, are presented for different viscosity contrasts, tube diameters, and flow rates. Physical mechanisms that determine these differences in dynamical state diagrams for various viscosity contrasts are discussed
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