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Dynamics of a multicomponent vesicle in shear flow.

ABSTRACT: We study the fully nonlinear, nonlocal dynamics of two-dimensional multicomponent vesicles in a shear flow with matched viscosity of the inner and outer fluids. Using a nonstiff, pseudo-spectral boundary integral method, we investigate dynamical patterns induced by inhomogeneous bending for a two phase system. Numerical results reveal that there exist novel phase-treading and tumbling mechanisms that cannot be observed for a homogeneous vesicle. In particular, unlike the well-known steady tank-treading dynamics characterized by a fixed inclination angle, here the phase-treading mechanism leads to unsteady periodic dynamics with an oscillatory inclination angle. When the average phase concentration is around 1/2, we observe tumbling dynamics even for very low shear rate, and the excess length required for tumbling is significantly smaller than the value for the single phase case. We summarize our results in phase diagrams in terms of the excess length, shear rate, and concentration of the soft phase. These findings go beyond the well known dynamical regimes of a homogeneous vesicle and highlight the level of complexity of vesicle dynamics in a fluid due to heterogeneous material properties.

SUBMITTER: Liu K

PROVIDER: S-EPMC5505236 | biostudies-literature | 2017 May

REPOSITORIES: biostudies-literature

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Dynamics of a multicomponent vesicle in shear flow.

Liu Kai K Marple Gary R GR Allard Jun J Li Shuwang S Veerapaneni Shravan S Lowengrub John J

Soft matter 20170425 19

We study the fully nonlinear, nonlocal dynamics of two-dimensional multicomponent vesicles in a shear flow with matched viscosity of the inner and outer fluids. Using a nonstiff, pseudo-spectral boundary integral method, we investigate dynamical patterns induced by inhomogeneous bending for a two phase system. Numerical results reveal that there exist novel phase-treading and tumbling mechanisms that cannot be observed for a homogeneous vesicle. In particular, unlike the well-known steady tank-t ...[more]

PMID: 28440378

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Project description:In this work, we compared the dynamics of motion in a linear shear flow of individual red blood cells (RBCs) from healthy and pathological donors (Sickle Cell Disease (SCD) or Sickle Cell-β-thalassemia) and of low and high densities, in a suspending medium of higher viscosity. In these conditions, at lower shear rates, biconcave discocyte-shaped RBCs present an unsteady flip-flopping motion, where the cell axis of symmetry rotates in the shear plane, rocking to and fro between an orbital angle ±ϕ observed when the cell is on its edge. We show that the evolution of ϕ depends solely on RBC density for healthy RBCs, with denser RBCs displaying lower ϕ values than the lighter ones. Typically, at a shear stress of 0.08 Pa, ϕ has values of 82 and 72° for RBCs with average densities of 1.097 and 1.115, respectively. Surprisingly, we show that SCD RBCs display the same ϕ-evolution as healthy RBCs of same density, showing that the flip-flopping behavior is unaffected by the SCD pathology. When the shear stress is increased further (above 0.1 Pa), healthy RBCs start going through a transition to a fluid-like motion, called tank-treading, where the RBC has a quasi-constant orientation relatively to the flow and the membrane rotates around the center of mass of the cell. This transition occurs at higher shear stresses (above 0.2 Pa) for denser cells. This shift toward higher stresses is even more remarkable in the case of SCD RBCs, showing that the transition to the tank-treading regime is highly dependent on the SCD pathology. Indeed, at a shear stress of 0.2 Pa, for RBCs with a density of 1.097, 100% of healthy RBCs have transited to the tank-treading regime vs. less than 50% SCD RBCs. We correlate the observed differences in dynamics to the alterations of RBC mechanical properties with regard to density and SCD pathology reported in the literature. Our results suggest that it might be possible to develop simple non-invasive assays for diagnosis purpose based on the RBC motion in shear flow and relying on this millifluidic approach.

Project description:d9 and d12 Mks were either cultured statically or subjected to shear flow for 30 min; at d9, half the Mks were placed back in culture for 30 min (60 min time point) Megakaryocytes (Mks) are exposed to shear flow as they migrate from the bone marrow hematopoietic compartment into circulation thus releasing platelets and pro/preplatelets directly into the blood stream. Shear forces have been now established as promoting Mk maturation and platelet biogenesis. In order to understand the underlying mechanisms that modulate the response of Mks to shear forces, we carried out transcriptional analysis on immature and mature stem cell-derived Mks that were exposed to physiologically-relevant shear (2.5 dyn/cm2). In immature (d9) Mks, shear exposure upregulated genes related to growth and Mk maturation, while in mature (d12) Mks, it upregulated genes involved in apoptosis and intracellular transport. Following shear-flow exposure, 6 AP-1 transcripts (ATF4, JUNB, JUN, FOSB, FOS, and JUND) were upregulated at d9 and two AP-1 proteins (JunD and c-Fos) were upregulated both at d9 and d12. Our data show that MAPK signaling is linked to both the shear-stress response and AP-1 upregulation. JNK phosphorylation increased significantly following shear stimulation, while JNK inhibition reduced shear-induced JunD protein expression. Although p38 phosphorylation did not increase following shear flow, its inhibition reduced shear-induced JunD and c-Fos protein expression. JNK inhibition reduced fibrinogen binding of d9 and d12 platelet-like particle s (PLPs) and P-selectin expression at d12 PLPs, while p38 inhibition reduced fibrinogen binding of d12 PLPs. Here we show that mechanotransduction of shear forces in Mks results in JNK activation, AP-1 upregulation, and downstream transcriptional changes that promote maturation of immature Mks and platelet biogenesis in mature Mks. Two- and Three-condition experiment (flow vs. static culture condition, d9 vs. d12, and 30 min vs. 60 min at d9); Biological replicates: 3; Technical replicates: 1 (dye-swap)

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Dynamics of a multicomponent vesicle in shear flow.

Publications

Dynamics of a multicomponent vesicle in shear flow.

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