Bulletin of the American Physical Society
67th Annual Meeting of the APS Division of Fluid Dynamics
Volume 59, Number 20
Sunday–Tuesday, November 23–25, 2014; San Francisco, California
Session R13: Biofluids: Membranes, Vesicles and Micelles |
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Chair: Petia Vlahovska, Brown University Room: 3020 |
Tuesday, November 25, 2014 1:05PM - 1:18PM |
R13.00001: Lipid Bilayer Vesicle Dynamics in AC Electric Fields Lane McConnell, Petia Vlahovska, Michael Miksis Vesicles are closed, fluid-filled lipid bilayers which are mechanically similar to biological cells and which undergo shape transitions in the presence of electric fields. Here we model the vesicle membrane as an infinitely thin, capacitive, area-incompressible interface with the surrounding fluids acting as charge-advecting leaky dielectrics. We then implement the boundary integral method to numerically investigate the dynamics of a vesicle in various AC electric field profiles. Our numerical results are then compared with recent small deformation theory and experimental data. We also note our observation of a new theoretical vesicle behavior that has yet to be observed experimentally. [Preview Abstract] |
Tuesday, November 25, 2014 1:18PM - 1:31PM |
R13.00002: Ellipsoidal Relaxation of Electrodeformed Vesicles Miao Yu, Rafael Lira, Karin Riske, Rumiana Dimova, Hao Lin Theoretical analysis and experimental quantification on the ellipsoidal relaxation of electrodeformed vesicles are presented. A closed-form solution is derived which predicts the aspect ratio as a function of time. Analysis of the solution and experimental data reveals good agreement, and two distinguishable regimes are identified. The ``entropic'' regime is dictated by the Helfrich constitutive relation, and in the ``constant tension'' regime the aspect ratio exhibits an exponential decay. Both the bending rigidity and initial membrane tension are accurately extracted. The relaxation of electroporated vesicles is also briefly discussed. This analytical approach provides a simple and powerful tool to query the mechanics of lipid membranes and similar soft materials. [Preview Abstract] |
Tuesday, November 25, 2014 1:31PM - 1:44PM |
R13.00003: Thermal undulations of biomimetic bilayer membranes in external fields Nico Fricke, Petia Vlahovska We study the influence of an applied electric field on the physical properties of fluid bilayer membranes. Global and regional analyses of the shape fluctuations of a giant quasi-spherical vesicle are used to determine membrane tension, bending rigidity, and shear viscosity from a time series of video- microscopy images. The parameters of the uniform electric field (frequency and amplitude) are chosen such that there is no global ellipsoidal vesicle deformation, and hence any renormalization of the tension and bending rigidity arise only from electric stress in the membrane. Using this approach we examine the effect of the electrotension on the main phase transition temperature of lipid membranes, where we observe that increasing field strength decreases, albeit slightly (about 0.1K), the melting temperature. [Preview Abstract] |
Tuesday, November 25, 2014 1:44PM - 1:57PM |
R13.00004: Experimental Methods to Observe Asymmetric Instability of Intermediate-Reduced-Volume Vesicles in Extensional Flow Joanna Dahl, Vivek Narsimhan, Bernardo Gouveia, Sanjay Kumar, Eric Shaqfeh, Susan Muller Vesicles provide an attractive model system to understand the deformation of living cells in response to mechanical forces. These enclosed lipid bilayer membranes are suitable for complementary theoretical and experimental analysis. A recent study (Narsimhan et al., J. Fluid Mech. 750: 144-190, 2014) predicted that intermediate-aspect-ratio vesicles break up asymmetrically in extensional flow. Upon infinitesimal perturbation to its shape, the vesicle stretches into an asymmetric dumbbell. In this work, we present preliminary results from cross-slot microfluidic experiments observing this instability. The onset of breakup depends on two non-dimensional parameters: reduced volume (vesicle asphericity) and capillary number (ratio of viscous to bending forces). We will present strategies for accurately measuring these quantities in order to plot a stability diagram. Specifically, we will describe our synthesis of floppy, intermediate-reduced-volume vesicles and our measurement of their bending moduli by analyzing membrane thermal fluctuations. We will discuss coupling particle-image velocimetry (PIV) with cross-slot trapping of vesicles to ensure that breakup occurs at the stagnation point. A preliminary phase diagram for asymmetric breakup will be reported. [Preview Abstract] |
Tuesday, November 25, 2014 1:57PM - 2:10PM |
R13.00005: ABSTRACT WITHDRAWN |
Tuesday, November 25, 2014 2:10PM - 2:23PM |
R13.00006: Nonlinear deformations of microcapsules in elongation flow Julien Deschamps, Cl\'ement de Loubens, Gwenn Boedec, Marc Georgelin, Marc Leonetti Soft microcapsules are drops bounded by a thin elastic shell made of cross-linked proteins. They have numerous applications for drug delivery in bioengineering, pharmaceutics and medicine, where their mechanical stability and their dynamics under flow are crucial. They can also be used as red blood cells models. Here, we investigate the mechanical behaviour of microcapsules made of albumine in strong elongational flow, up to a stretching of 180{\%} just before breaking. The set-up allows us to visualize the deformed shape in the two perpendicular main fields of view, to manage high capillary number and to manipulate soft microcapsules. The steady-state shape of a capsule in the planar elongational flow is non-axisymmetric. In each cross section, the shape is an ellipse but with different small axis which vary in opposite sense with the stretching. Whatever the degree of cross-linking and the size of the capsules, the deformations followed the same master-curve. Comparisons between numerical predictions and experimental results permit to conclude unambiguously that the more properly strain-energy model of membrane is the generalized Hooke model. [Preview Abstract] |
Tuesday, November 25, 2014 2:23PM - 2:36PM |
R13.00007: Effect of bending on the dynamics and wrinkle formation for a capsule in shear flow Anne-Virginie Salsac, Claire Dupont, Dominique Barthes-Biesel, Marina Vidrascu, Patrick Le Tallec When microcapsules are subjected to an external flow, the droplets enclosed within a thin hyperelastic wall undergo large deformations, which often lead to buckling of the thin capsule wall. The objective is to study numerically an initially spherical capsule in shear flow and analyze the influence of the membrane bending rigidity on the capsule dynamics and wrinkle formation. The 3D fluid-structure interactions are modeled coupling a boundary integral method to solve for the internal and external Stokes flows with a thin shell finite element method to solve for the wall deformation. Hyperelastic constitutive laws are implemented to model the deformation of the capsule mid-surface and the generalized Hooke's law for the bending effects. We show that the capsule global motion and deformation are mainly governed by in-plane membrane tensions and are marginally influenced by the bending stiffness Ks. The bending stiffness, however, plays a role locally in regions of compressive tensions. The wrinkle wavelength depends on Ks following a power law, which provides an experimental technique to determine the value of Ks through inverse analysis. [Preview Abstract] |
Tuesday, November 25, 2014 2:36PM - 2:49PM |
R13.00008: Swinging of two-domains vesicles in shear flow Annie Viallat, Simon Tusch, Kamel Khelloufi, Marc Leonetti Giant lipid vesicles and red blood cells in shear flow at low shear rates tank tread (TT) at small viscosity ratio between the inner particle volume and the external fluid, and flip or tumble (T) at large viscosity ratio. The phase diagram of motion of red blood cells is however much more complex. Swinging superimposes to TT, cells wobble and roll rather than tumble with increasing shear rate and present a shear-rate driven transition between TT to T. These features are attributed to the shear elasticity and the non spherical stress-free shape of the cell membrane, which stores shear elastic energy as a function of the relative position of its elements. We have created vesicles with a phase diagram of motion comparable to that of red blood cells by preparing membranes with two lipids and cholesterol. These membranes present two domains separated by a contact line. The line has a tension energy that depends on its relative position on the vesicle. Similarly to red blood cells, two-domains vesicles swing and wobble. An analytical model where line tension energy is added to the Keller and Skalak's model fits our experimental data without any adjustable parameter. Our experiments and model shed light on the motion of deformable particles in shear flow. [Preview Abstract] |
(Author Not Attending)
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R13.00009: Three-dimensional numerical simulation of red blood cell motion in Poiseuille flows Lingling Shi, Tsorng-Whay Pan, Roland Glowinski An immersed boundary method based on a finite element method has been successfully combined with an elastic spring network model for simulating the dynamical behavior of a red blood cell (RBC) in Poiseuille flows. This elastic spring network preserves the biconcave shape of the RBC in the sense that after the removal of the body force for driving the Poiseuille flow, a RBC with its typical parachute shape in a tube does restore its biconcave resting shape. As a benchmark test, the relationship between the deformation index and the capillary number of the RBCs flowing through a narrow cylindrical tube has been validated. For the migration properties of a single cell in a slit Poiseuille flow, a slipper shape accompanied by a cell membrane tank-treading motion is obtained for Re $\ge 0.03$ and the cell mass center is away from the center line of the channel due to its asymmetric slipper shape. For the lower Re $\le 0.0137$, a RBC with almost undeformed biconcave shape has a tumbling motion. A transition from tumbling to tank-treading happens at the Reynolds number between 0.0137 and 0.03. In slit Poiseuille flow, RBC can also exhibit a rolling motion like a wheel during the migration. The lower Reynolds number is, the longer the rolling motion lasts. [Preview Abstract] |
Tuesday, November 25, 2014 3:02PM - 3:15PM |
R13.00010: Mesoscopic Modeling of Thrombus Formation and Growth: Platelet Deposition in Complex Geometries Alireza Yazdani, George Karniadakis Haemodynamics and blood rheology are important contributing factors to thrombus formation at a vulnerable vessel wall, and adhesion of platelets to a vascular surface, particularly in regions of flow stagnation, recirculation and reattachment is significantly important in formation of thrombi. For example, haemodynamic micro-environment can have effects on thrombosis inside the atherosclerotic plaques and aneurysms. To study these effects, we have developed and validated a model for platelet aggregation in blood flow using Dissipative Particle Dynamics (DPD) method. In this model platelets are considered as single DPD particles interacting with each other via Morse potential once activated. We assign an activation delay time to each platelet such that they remain passive during that time. We investigate the effect of different geometries on platelet aggregation by considering arterial stenosis at different levels of occlusion, and aneurysms of different shapes and sizes. The results show a marked increase in platelet aggregation within the boundaries of deceleration zone by increasing the degree of stenosis. Further, we observe enhanced platelet margination and wall deposition in the presence of red blood cells. [Preview Abstract] |
Tuesday, November 25, 2014 3:15PM - 3:28PM |
R13.00011: Topology, Energetics and Rheology of Surfactant Micelles Radhakrishna Sureshkumar, Subas Dhakal, Abhinandan Sambasivam A rich variety of self-assembled structures of amphiphilic molecules, ranging from spherical and cylindrical shapes to topologically complex networks consisting of branches and loops, is unraveled through large scale Molecular Dynamic simulations that account for explicit solvent, electrostatic and hydrodynamic interactions. The simulations employ a coarse grained force field, benchmarked against atomistic simulations (Sangwai and Sureshkumar, Langmuir, 27, 6628 (2011); 28, 1127 (2012)), to describe inter-molecular forces. Analysis of these structures allows for the first time to directly determine certain fundamental length scales, e.g. persistence and contour lengths, mesh size, as well as the end cap energy, which dictate the rheological properties and flow phenomena in micellar fluids. The much debated anomalous viscosity variations with respect to salt concentration can be understood based on the underlying morphological changes (http://arxiv.org/abs/1407.5086). This, and the effect of nanoparticle addition to the network structure and flow properties, will be discussed. [Preview Abstract] |
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