A new look at blood shear-thinning

TL;DR

This study investigates red blood cell dynamics under various flow conditions, revealing complex shape transitions that challenge existing beliefs and have implications for understanding blood flow in health and disease.

Contribution

It provides new experimental and simulation evidence of RBC shape transitions under shear stress, contradicting previous assumptions about cell alignment and elongation.

Findings

RBCs undergo tumbling, rolling, and shape transformations with increasing shear stress.

Shape transitions are influenced by plasma composition and membrane properties.

Results have implications for understanding pathological blood flow behaviors.

Abstract

Blood viscosity decreases with shear stress, a property essential for an efficient perfusion of the vascular tree. Shear-thinning is intimately related to the dynamics and mutual interactions of red blood cells (RBCs), the major constituents of blood. Our work explores RBCs dynamics under physiologically relevant conditions of flow strength, outer fluid viscosity and volume fraction. Our results contradict the current paradigm stating that RBCs should align and elongate in the flow direction thanks to their membrane circulation around their center of mass, reducing flow-lines disturbances. On the contrary, we observe both experimentally and with simulations, rich morphological transitions that relate to global blood rheology. For increasing shear stresses, RBCs successively tumble, roll, deform into rolling stomatocytes and finally adopt highly deformed and polylobed shapes even for semi-dilute volume fractions analogous to microcirculatory values. Our study suggests that any pathological change in plasma composition, RBCs cytosol viscosity or membrane mechanical properties will impact the onset of shape transitions and should play a central role in pathological blood rheology and flow behavior.