Abstract
Blood is a dense suspension of soft non-Brownian cells of unique importance. Physiological blood flow involves complex interactions of blood cells with each other and with the environment due to the combined effects of varying cell concentration, cell morphology, cell rheology, and confinement. We analyze these interactions using computational morphological image analysis and machine learning algorithms to quantify the non-equilibrium fluctuations of cellular velocities in a minimal, quasi-two-dimensional microfluidic setting that enables high-resolution spatio-temporal measurements of blood cell flow. In particular, we measure the effective hydrodynamic diffusivity of blood cells and analyze its relationship to macroscopic properties such as bulk flow velocity and density. We also use the effective suspension temperature to distinguish the flow of normal red blood cells and pathological sickled red blood cells and suggest that this temperature may help to characterize the propensity for stasis in Virchow's Triad of blood clotting and thrombosis.
Highlights
Red blood cells are the major component of blood and with a radius of,4 mm and a thickness of,1–2 mm are sufficiently large that the effects of thermal fluctuations are typically negligible, i.e. their equilibrium diffusivity is very small
We find that an increase in Vbulk from rest to about 50 mm/s is associated with a change in dynamics from stationary through sub-diffusive to diffusive
Hydrodynamic interactions between red blood cells lead to velocity fluctuations and diffusive dynamics of the individual cells
Summary
When suspensions of these soft cells are driven by pressure gradients and/or subject to shear, complex multi-particle interactions give rise to local concentration and velocity gradients which drive fluctuating particle movements [2,3,4]. We complement the large body of work characterizing the flow of sheared and sedimenting rigid particulate suspensions [7,8,9,10,11] and here study the statistical dynamics of pressure-driven soft concentrated suspensions while making connections to human physiology and disease. We provide quantitative evidence that there is heterogeneity in cellular velocity and density This heterogeneity may play a role in the slow flow or stasis that can lead to the collective physiological and pathological processes of coagulation or thrombosis, as Virchow noted more than 100 years ago [12]
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