Flow-Induced Transitions of Red Blood Cell Shapes under Shear

Abstract

A recent study of red blood cells (RBCs) in shear flow [Lanotte et al., Proc. Natl. Acad. Sci. U.S.A. 113, 13289 (2016)PNASA60027-842410.1073/pnas.1608074113] has demonstrated that RBCs first tumble, then roll, transit to a rolling and tumbling stomatocyte, and finally attain polylobed shapes with increasing shear rate, when the viscosity contrast between cytosol and blood plasma is large enough. Using two different simulation techniques, we construct a state diagram of RBC shapes and dynamics in shear flow as a function of shear rate and viscosity contrast, which is also supported by microfluidic experiments. Furthermore, we illustrate the importance of RBC shear elasticity for its dynamics in flow and show that two different kinds of membrane buckling trigger the transition between subsequent RBC states.

High-throughput microfluidic characterization of erythrocyte shape and mechanical variability

“…This is due to the fact that high viscosity contrasts suppress membrane tank-treading, thereby making the slipper state unfavorable. In fact, RBCs at λ = 5 in simple shear flow do not exhibit tank-treading motion at all (9,36). However, under strong confinement, membrane tank-treading becomes possible, as we observe slippers in the diagram in Fig.…”

“…Empirical approximation of the inherent variation in RBC shear elasticity leads to RBC state distributions, which agree well with experimental observations. Furthermore, the experiments show the existence of tumbling polylobe shapes in large enough channels at high flow rates, which were before only observed in pure shear flow (9,36). The combination of experimental and simulation results allows us to fill several gaps in understanding of RBC behavior in microchannels and to make a step toward a quantitative characterization of RBC mechanical properties and their variability.…”

“…2I). Polylobe shapes were observed at high shear rates in simple shear flow both experimentally and numerically (9,36).…”

“…The model also contains area-and volumeconservation constraints to mimic incompressibility of the lipid bilayer and cell's cytosol. The RBC model employs a stress-free shape of the elastic spring network, corresponding to a spheroidal shape with a reduced volume of 0.96, because recent simulation studies (36,39,40) suggest that a nearly spherical stress-free shape best reproduces experimental results for the tumbling-to-tank-treading transition at low viscosity contrasts (41,42). Alternatively, a stress-free condition can also be incorporated into the bending potential through an inhomogeneous spontaneous curvature (43).…”

“…Additionally, the presence of membrane viscosity, which was not modeled in simulations, would further increase the viscous resistance for cell deformation (56,57). A high viscosity contrast is known to prohibit tank-treading motion of vesicles (58,59) and RBCs (9,36) in pure shear flow. Similarly, RBC tank-treading in a channel may be hindered by a high enough viscosity contrast, resulting in a polylobe.…”