Predicting human blood viscosity in silico

Abstract

The viscosity of blood has long been used as an indicator in the understanding and treatment of disease, and the advent of modern viscometers allows its measurement with ever-improving clinical convenience. However, these advances have not been matched by theoretical developments that can yield a quantitative understanding of blood's microrheology and its possible connection to relevant biomolecules (e.g., fibrinogen). Using coarse-grained molecular dynamics and two different red blood cell models, we accurately predict the dependence of blood viscosity on shear rate and hematocrit. We explicitly represent cell-cell interactions and identify the types and sizes of reversible rouleaux structures that yield a tremendous increase of blood viscosity at low shear rates. We also present the first quantitative estimates of the magnitude of adhesive forces between red cells. In addition, our simulations support the hypothesis, previously deduced from experiments, of yield stress as an indicator of cell aggregation. This non-Newtonian behavior is analyzed and related to the suspension's microstructure, deformation, and dynamics of single red blood cells. The most complex cell dynamics occurs in the intermediate shear rate regime, where individual cells experience severe deformation and transient folded conformations. The generality of these cell models together with single-cell measurements points to the future prediction of blood-viscosity anomalies and the corresponding microstructures associated with various diseases (e.g., malaria, AIDS, and diabetes mellitus). The models can easily be adapted to tune the properties of a much wider class of complex fluids including capsule and vesicle suspensions.blood rheology | blood modeling | shear thinning | aggregation force | dissipative particle dynamics R heological and material properties of cell, capsule, and vesicle suspensions have many applications in medicine, biology, engineering, and materials science. One of the main examples of such suspensions is blood, which consists of RBCs, predominant by volume, and a small fraction of other cells and proteins suspended in the plasma. Understanding blood flow and its relation to cellular properties and interactions may lead to advances in biomedical applications (e.g., drug delivery, blood substitutes). Moreover, a change in blood rheological and flow properties is often associated with hematological diseases or disorders (e.g., sickle-cell anemia, malaria), and therefore the viscosity of blood has long been used as an indicator in the understanding and treatment of disease.Modern rheometry techniques and instruments yield reliable measurements of macroscopic properties of cell suspensions with ever-improving convenience-for example, the bulk properties of blood measured in various laboratories (1-6). Virtually all bloodviscosity measurements are necessarily in vitro, and before newly drawn blood is introduced into a viscometer it must at least be stabilized with an anticoagulant, which is then called "whole blood." Under flow...

Red cells’ dynamic morphologies govern blood shear thinning under microcirculatory flow conditions

“…Such a viscous environment around single cells is supposed to mimic the effective high-shearrate viscosity of the crowded conditions present in WB (17). Therefore, the shear-thinning paradigm is rooted in RBCs' ability to tank-tread whatever the Ht in response to high shear stresses (7).…”

“…Macromolecules dispersed in the plasma, such as fibrinogen, induce an attractive force between RBCs, leading to their aggregation (5). Because RBCs have a biconcave disk-like shape at rest, they form long floppy rouleaux structures that can reversibly and continuously break down to single flowing discocytes for increasing shear rates up to tens of seconds −1 (6,7). This change in microstructure is indeed accompanied by a strong viscosity drop from ∼ 100 cP down to about ∼ 10 cP (3).…”

Full dynamics of a red blood cell in shear flow

“…Furthermore, numerical predictions of RBC deformations show significant discrepancies with experimental observations. Indeed, experiments report only the stationary stretched shape of cells steadily aligned in the flow at high shear rates, whereas recent numerical studies predict "breathing" dynamic states with strong shape deformations at low shear rates for both RBCs and elastic capsules (9)(10)(11)(12)(13)(14)(15)(16).…”

“…To date, there has been little experimental work on the connection between the mechanical properties of RBCs and their dynamics in shear flow (5-8), compared with the many numerical and theoretical recent studies reported for capsules (9)(10)(11) and red blood cells (12)(13)(14)(15)(16). Surprisingly, all investigations dealing with RBC orientation in flow focus on a very particular case in which the axis of symmetry of the cell lies in the shear plane.…”

“…The KS model modified to account for membrane elasticity and shape memory, developed by Abkarian et al (AFV) (7) and by Skotheim and Secomb (SS) (14), semiquantitatively recovers these dynamic states and their transition. Since then, this field has been very active and many theoretical and numerical approaches have been developed (9)(10)(11)(12)(13)(14)(15)(16), which account for the most important cell mechanical parameters and allow shape deformation. They recover the various regimes of motion, except intermittency, which is still controversial, but also predict new regimes associated with strong unsteady deformations that have never been seen experimentally.…”