Bulletin of the American Physical Society
64th Annual Meeting of the APS Division of Fluid Dynamics
Volume 56, Number 18
Sunday–Tuesday, November 20–22, 2011; Baltimore, Maryland
Session G29: Biofluids: Cellular III: Vesicles |
Hide Abstracts |
Chair: Thomas Powers, Brown University Room: Ballroom III |
Monday, November 21, 2011 8:00AM - 8:13AM |
G29.00001: Molecular Transport across Small Blood Vessels Axel Guenther, Zhamak Abdidezfooli, Sascha Pinto, Steffen-Sebastian Bolz Small blood vessels dominate molecular transport of small and large molecules due to their large cumulative surface area. However, systematically probing specific transport mechanisms under well defined and physiologically meaningful conditions is challenging. We present the first microfluidic approach that allows the investigation of molecular transport across intact small blood vessels. Functionally intact mouse mesenteric arteries (150-300 micrometers in diameter) are perfused with fluorescent markers. The permeation rate across the vessel wall is locally deduced by laser scanning confocal microscopy and particle image velocity measurements in combination with a transport model, and by a global fluorescence spectroscopy measurement. [Preview Abstract] |
Monday, November 21, 2011 8:13AM - 8:26AM |
G29.00002: The Brownian dynamics of a lipid vesicle Hong Zhao, Eric Shaqfeh We propose a Brownian dynamics simulation method to study the motion of a lipid vesicle in a suspending fluid. The lipid bilayer of the vesicle is modeled as a two-dimensional fluidic membrane with bending resistance and a high local area dilatational modulus. Using a Stokes flow boundary integral equation method, we calculate the grand mobility tensor of the deformable membrane at arbitrary viscosity ratio between the fluid inside and outside the vesicle. The fluctuation--dissipation theorem, as well as the drifting due to the configuration dependence of the diffusivity tensor, are rigorously accounted for. The flow transitions (tank-treading, tumbling and trembling) and the particle stresslet for an athermal vesicle in a simple shear flow calculated by the present method are in good agreement with existing results by a spectral boundary integral equation method. We demonstrate that the effect of Brownian motion is most significant for a tumbling vesicle. The thermal fluctuation tilts the vesicle off the shear plane, and the disruption of the originally two-dimensional tumbling orbit results in a qualitatively different three-dimensional ``wobbling'' motion. The change to the suspension rheology due to the altered dynamics is discussed. [Preview Abstract] |
Monday, November 21, 2011 8:26AM - 8:39AM |
G29.00003: Dynamics of Lipid Bilayer Vesicles and Droplets in DC Electric Fields Lane McConnell, Petia Vlahovska, Michael Miksis Closed lipid bilayers (vesicles) serve as a model system to study the mechanics of the biomembranes encapsulating cells and cellular organelles. We present a numerical investigation using the Boundary Integral Method of the dynamics and stability of a charge-free lipid bilayer vesicle in a uniform DC electric field. The lipid membrane is modeled as a zero-thickness, capacitive, area-incompressible interface, and bulk fluids are assumed to be leaky dielectrics. Vesicle shape is determined by balancing the electric, hydrodynamic, bending, and surface tension stresses along the interface. Investigations of vesicle response to electric fields are limited, but recent small deformation analysis has revealed several interesting phenomena not observed with droplets, including transitions from oblate to prolate shapes. Our numerical investigations highlight the differences in the behavior of vesicles and drops due to the capacitive nature of the bilayer membrane. [Preview Abstract] |
Monday, November 21, 2011 8:39AM - 8:52AM |
G29.00004: Vesicle Shape Transformations Driven by Active and Spontaneous Lipid Flip-flop Thomas Powers, Elnaz Baum-Snow The lipid composition of cell membranes is created and maintained in part by flippases, enzymes that translocate lipid molecules from one layer of the bilayer membrane to the other. We study how lipid translocation can affect membrane shape, using a cylindrical vesicle as a simple model system. For a short pulse of flippase activity, in which a fraction of lipids are flipped from one layer to the other, we calculate the fraction of flipped lipids that makes the cylinder unstable to a periodic modulation in its radius, as well as the growth rate of perturbations of different wavenumber. We also study the cases of continuous flippase activity and spontaneous flip-flop. [Preview Abstract] |
Monday, November 21, 2011 8:52AM - 9:05AM |
G29.00005: Dynamics and phase diagrams for highly non-spherical vesicles in shear flow computed with Loop subdivision surfaces Andrew Spann, Hong Zhao, Eric Shaqfeh Vesicles, particularly those with a low volume to surface area ratio, are challenging to simulate due to the presence of a surface incompressibility constraint and a bending energy that requires a highly accurate estimate of curvature. A boundary integral method based on Loop subdivision surfaces on an unstructured mesh is used to compute phase diagrams and stress dynamics for highly non-spherical vesicles in shear flow. In addition to the most commonly studied prolate family of vesicles, we also investigate the biconcave and stomatocyte shapes. We chronicle the decrease in the viscosity ratio threshold needed to trigger transition between the regimes of tank treading, trembling, tumbling, and kayaking as the reduced volume ratio of a prolate vesicle decreases. For biconcave shapes, we observe three regimes: conversion to prolate, tank treading, and tumbling. We find that biconcave tumbling near the critical viscosity ratio is not merely a rotation motion and includes noteworthy stretching in the vorticity direction. [Preview Abstract] |
Monday, November 21, 2011 9:05AM - 9:18AM |
G29.00006: Electrohydrodynamics of bilayer membranes Paul Salipante, Rumiana Dimova, Petia Vlahovska Membranes that encapsulate cells and internal cellular organelles are composed primarily of lipid bilayers. Biomimetic membranes assembled from polymers are used as vectors for targeted drug delivery. We investigate the deformation and stability of fluid membranes made of lipids or polymers in uniform electric fields. A frequency dependent shape deformation of vesicles (closed membranes) in AC fields elucidates the capacitive nature of the membrane and provides a new experimental method for measuring membrane capacitance. Compared to lipid membranes, we find that polymer membranes have an order of magnitude lower capacitance, which correlates with their larger thickness. Upon application of the electric field, the dynamic response of the vesicle is sensitive to membrane viscosity, while the steady state shape is governed by membrane tension and bending stiffness. Strong DC pulses, typically used in cell electroporation, is shown to induce an instability in both lipid and polymer membranes. The instability leads to vesicle collapse, where the timescale of collapse shows a t$\sim$1/E$^2$ dependence. [Preview Abstract] |
Monday, November 21, 2011 9:18AM - 9:31AM |
G29.00007: The relaxation of tweezed giant unilamellar vesicles Wolfgang Losert, Hernan Zhou, Beatriz Burrola Gabilondo, Willem van de Water We study the shape relaxation of spherical giant unilamellar vesicles which have been deformed far from equilibrium into ellipsoids using optical tweezers. The relaxation back to a sphere is determined by elastic constants of the vesicles, and their excess area, as well as by low Reynolds number fluid flow. The properties of each vesicle are learned from observing its shape fluctuations in thermal equilibrium. We will critically evaluate the spectroscopic techniques used to find those properties. The relaxation time of the stretched vesicles could be compared favorably to a simple formula which encompasses the joint effect of membrane rigidity and fluid flow. The time constant of the stretched vesicle is slower than that of its thermal fluctuations, which agrees with a recent theory, however, it is still one order of magnitude faster than predicted. [Preview Abstract] |
Monday, November 21, 2011 9:31AM - 9:44AM |
G29.00008: Viscoelastic properties of vascular endothelial cells exposed to uniaxial stretch Kathryn Osterday, Thomas Chew, Phillip Loury, Jason Haga, Juan C. del Alamo, Shu Chien Vascular endothelial cells (VECs) line the interior of blood vessels and regulate a variety of functions in the cardiovascular system. It is widely accepted that VECs will remodel themselves in response to mechanical stimuli, but few studies have analyzed the mechanical properties of these cells under stretch. We hypothesize that uniaxial stretch will cause an anisotropic realignment of actin filaments, and a change in the viscoelastic properties of the cell. To test this hypothesis, VECs were grown on a thin, transparent membrane mounted on a microscope. The membrane was stretched, consequently stretching the cells. Time-lapse sequences of the cells were taken every hour with a time resolution of 10 Hz. The random trajectories of intracellular endogenous particles were tracked using in-house algorithms. These trajectories were analyzed using a novel particle tracking microrheology formulation that takes into account the anisotropy of the cytoplasm of VECs. [Preview Abstract] |
Monday, November 21, 2011 9:44AM - 9:57AM |
G29.00009: The evolution of a sessile vesicle's shape during desiccation processes Maurice Blount, Michael Miksis, Stephen Davis We present a model that describes the shape evolution of a vesicle that is attached to a substrate. During desiccation processes the vesicle contains an aqueous solution of sugar and is surrounded by an aqueous solution of sugar of higher concentration. Transport of water across the vesicle's semi-permeable membrane is driven by concentration and pressure gradients applied across it. As water is drawn out of the vesicle, its volume decreases but its surface area is conserved owing to the membrane's incompressibility. The consequent buckling of the membrane is impeded by its bending stiffness and by the viscous stresses in the flow that are generated by the membrane's motion. We use our model to describe the various physical nonlinear effects that evolve during the process. [Preview Abstract] |
Monday, November 21, 2011 9:57AM - 10:10AM |
G29.00010: Numerical Analysis of Vesicle Dynamics in Linear Shear Flow Alireza Yazdani, Prosenjit Bagchi There has been an ongoing debate in the vesicle research community with regard to the dependence of the vesicle dynamics on the controlling parameters, namely, the shear rate, viscosity ratio, and vesicle excess area. Theoretical works by Misbah and coworkers [e.g., Kaoui et al, Phys Rev E, \textbf {80}, 061905 (2009)] predict that the dynamics depends on all three parameters, whereas experimental works by Steinberg's group [e.g., Zabusky et al, Phys Fluids, \textbf {23}, 041905 (2011)] suggest only two parameters. In order to provide further insight, we consider 3D numerical simulations using a front-tracking method. We model the membrane bending resistance using the Helfrich formulation [Zhong-can \& Helfrich, Phys Rev A, \textbf {39}, 5280 (1989)], and the area dilatation using the strain energy function developed by Skalak et al [Biophys J. \textbf {13}, 245, (1973)]. The simulations successfully predict three different dynamical regimes, namely, the tank-treading, vascillating-breathing, and tumbling. Quantitative comparisons are made with the theoretical results as well as the experimental data. We find that the tank-treading inclination angle and the tank-treading-to-tumbling transition threshold is weakly dependent on the shear rate. We further provide phase diagrams, and discuss the role of the controlling parameters on the transition. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2022 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
1 Research Road, Ridge, NY 11961-2701
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700