Bulletin of the American Physical Society
68th Annual Meeting of the APS Division of Fluid Dynamics
Volume 60, Number 21
Sunday–Tuesday, November 22–24, 2015; Boston, Massachusetts
Session E24: Biofluids: Vesicles and Micelles |
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Chair: Tsorng-Whay Pan, University of Houston Room: 302 |
Sunday, November 22, 2015 4:50PM - 5:03PM |
E24.00001: The dynamics of inextensible capsules in shear flow under the effect of the natural state Tsorng-Whay Pan, Xiting Niu, Roland Glowinski The effect of the natural state on the motion of an inextensible capsule in two-dimensional shear flow has been studied numerically. The energy barrier based on such natural state plays a role for having the transition between two well-known motions, tumbling and tank-treading (TT) with the long axis oscillating about a fixed inclination angle (a swinging mode), when varying the shear rate. Between tumbling and TT with a swinging mode, the intermittent region has been obtained for the capsule with a biconcave rest shape. The estimated critical value of the swelling ratio for having the intermittent region is $< 0.7$, i.e., the capsule with the rest shape closer to a full disk has no intermittent behavior. The capsule intermittent behavior is a mixture of tumbling and TT. Just like the TT with a swinging mode, which can be viewed as TT with an incomplete tumbling, the membrane tank-treads backward and forward within a small range while tumbling. The transition between tumbling and TT with a swinging mode has been studied. [Preview Abstract] |
Sunday, November 22, 2015 5:03PM - 5:16PM |
E24.00002: Off-plane motion of an oblate capsule in simple shear flow Anne-Virginie Salsac, Claire Dupont, Fabien Delahaye, Dominique Barthes-Biesel As biomimetic models of red blood cells, non-spherical liquid-core capsules have received great attention to understand their dynamics in simple shear flow. They are also of interest for drug delivery applications having higher diffusion properties than spherical ones. Most studies have modeled the capsule motion placing the revolution axis in the shear plane, which is an equilibrium configuration in Stokes flow conditions and thus a special case. The present objective is to determine the stability of the equilibrium configurations of oblate capsules and investigate the effects of the capillary number \textit{Ca}, inner-to-outer viscosity ratio $\lambda $ and initial orientation. To solve the fluid-structure interaction problem, we use a numerical model coupling a finite element method for the capsule deformation with a boundary integral method for the internal and external flows. The equilibrium motions are found to be independent of the capsule initial inclination and to depend only on \textit{Ca}. The tumbling and swinging regimes (characterized by the revolution axis in the shear plane) are found to be stable only until \textit{Ca} $\sim$ 0.9. Above, the capsule takes a rolling motion with its revolution axis normal to the shear plane. For $\lambda $ \textgreater 4, only tumbling is stable at low \textit{Ca} and rolling at higher \textit{Ca}. [Preview Abstract] |
Sunday, November 22, 2015 5:16PM - 5:29PM |
E24.00003: Quantifying mixing in vesicle suspensions using numerical simulations in two dimensions Gokberk Kabacaoglu, George Biros, Bryan Quaife Vesicles, which resist bending and are locally inextensible, serve as an experimental and numerical proxy for red blood cells. In this work, we study the effect of the presence of vesicles to mixing. The motivating application is the study of transport phenomena in microcirculation. We investigate transport specifically in a Couette apparatus, which is governed by an advection-diffusion equation, and we consider mixing in the absence and presence of vesicles using numerical simulations in two dimensions. The advection-diffusion equation is discretized spectrally in space, and with a second-order L-stable Strang splitting in time. To our knowledge, there are no universally accepted measures of mixing. Here, we study two measures: the ``mix-norm'' defined by a Sobolev norm of negative index and a standard moment fluctuation of the transported species. We define mixing efficiency in terms of mixing measure in the absence of vesicles relative to the measure in the presence of vesicles. We then study the correlation of mixing efficiency with the Peclet number, the volume fraction of the vesicle suspension, and the type of initial conditions. [Preview Abstract] |
Sunday, November 22, 2015 5:29PM - 5:42PM |
E24.00004: Hydrodynamic and macromolecules induced clusters of red blood cells in microcapillary flow Viviana Claveira, Othmane Aouane, Gwennou Coupier, Chaouqi Misbah, Manouk Abkarian, Christian Wagner Recent studies have been shown that despite the large shear rates, the presence of either fibrinogen or the synthetic polymer dextran leads to an enhanced formation of robust clusters of RBC in microcapillaries under flow conditions. The contribution of hydrodynamic interactions and interactions induced by the presence of macromolecules in the cluster formation has not been established. In order to elucidate this mechanism, we compare experimentally in microchannels under flow condition, the pure hydrodynamic cluster formation of RBCs and the cluster formation of RBCs in the presence of macromolecules inducing aggregation. The results reveal strong differences in the cluster morphology. Emphasizing on the case of clusters formed by two cells, the surface to surface interdistances between the cells in the different solutions shows a bimodal distribution. Numerical simulations based on the boundary integral method showed a good agreement with the experimental findings. [Preview Abstract] |
Sunday, November 22, 2015 5:42PM - 5:55PM |
E24.00005: Multiscale modeling of mechanosensing channels on vesicles and cell membranes in 3D constricted flows and shear flows Zhangli Peng, On Shun Pak, Yuan-Nan Young, Allen Liu, Howard Stone We investigate the gating of mechanosensing channels (Mscls) on vesicles and cell membranes under different flow conditions using a multiscale approach. At the cell level (microns), the membrane tension is calculated using a 3D two-component whole-cell membrane model based on dissipative particle dynamics (DPD), including the cortex cytoskeleton and its interactions with the lipid bilayer. At the Mscl level (nanometers), we predict the relation between channel gating and the membrane tension obtained from a cell-level model using a semi-analytical model based on the bilayer hydrophobic mismatch energy. We systematically study the gating of Mscls of vesicles and cell membranes in constricted channel flows and shear flows, and explore the dependence of the gating on flow rate, cell shape and size. The results provide guidance for future experiments in inducing Mscl opening for various purposes such as drug delivery. [Preview Abstract] |
Sunday, November 22, 2015 5:55PM - 6:08PM |
E24.00006: Resolving lubrication layers in immersed boundary method simulations of vesicular transport in dendritic spines Thomas Fai, Remy Kusters, Chris Rycroft Our understanding of how neuronal connections in the brain are maintained and reorganized is being revolutionized by new experimental and computational techniques. Existing high-resolution 3D images show that neuronal axons often terminate onto micron-sized structures known as dendritic spines, which are characterized by their thin necks and bulbous heads. Vesicles containing membrane receptors must deform significantly to squeeze into the bulbous heads of the spines, but more quantitative estimates of the force and energy required are still lacking. We have used three-dimensional immersed boundary method simulations to capture the fluid dynamics of vesicle transport into spines. We vary the applied force and neck geometry to identify the region in phase space in which the vesicle can squeeze into the spine. These results are compared to pass-stuck diagrams computed previously in the case of vesicles squeezing through open channels with rigid walls. The resulting force estimates are found to be consistent with the physiological density of motor proteins. Resolving the thin lubricating layers between the vesicles and spine poses significant numerical challenges, and we have used elements from lubrication theory to help resolve these boundary layers. [Preview Abstract] |
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