Bulletin of the American Physical Society
63rd Annual Meeting of the APS Division of Fluid Dynamics
Volume 55, Number 16
Sunday–Tuesday, November 21–23, 2010; Long Beach, California
Session RK: Biofluids: Cellular IV |
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Chair: Yeng-Long Chen, Academia Sinica Room: Long Beach Convention Center 201B |
Tuesday, November 23, 2010 3:05PM - 3:18PM |
RK.00001: Vesicle Electrohydrodynamics Jonathan Schwalbe, Petia Vlahovska, Michael Miksis A small amplitude perturbation analysis is developed to describe the effect of a uniform electric field on the dynamics of a lipid bilayer vesicle in a simple shear flow. All media are treated as leaky dielectrics and fluid motion is described by the Stokes equations. The instantaneous vesicle shape is obtained by balancing electric, hydrodynamic, bending, and tension stresses exerted on the membrane. Solutions are presented as a function of the physical parameters. It is shown that in the absence of ambient shear flow, it is possible that an applied step-wise uniform DC electric field could cause the vesicle shape to evolve from oblate to prolate over time if the encapsulated fluid is less conducting than the suspending fluid. For a vesicle in ambient shear flow, the electric field modifies, and may even eliminate, the tank-treading to tumbling transition. [Preview Abstract] |
Tuesday, November 23, 2010 3:18PM - 3:31PM |
RK.00002: The dynamics of a lipid vesicle in shear flow Hong Zhao, Eric S.G. Shaqfeh The dynamics of a lipid vesicle in a simple shear flow, where the lipid membrane is modeled as a two dimensional incompressible fluid with bending stiffness, is solved by a high-fidelity spectral boundary integral formulation. We combine our direct numerical simulation (DNS) with a linear stability analysis to solve the exact critical internal/external viscosity ratio for the transition from the steady tank-treading motion to the unsteady trembling/tumbling motions at different shear rates. It is demonstrated that a fourth (and higher) order spherical harmonic expansion of the vesicle shape is necessary for obtaining quantitatively correct transition boundaries. The particle stresslets in different flow regimes are calculated, and the consequences for the rheology of a dilute suspension is discussed. In addition, our DNS reveals a family of time-periodic and out-of-shear-plane vesicle motion patterns, where the orientation of principle axes follow orbits that resemble but are fundamentally different from the classical Jeffery orbits of rigid particles due to the vesicle's deformability. The effect of wall boundaries on the vesicle motion is then investigated within our DNS by using the known Green's function for a no-slip walls at zero Reynolds number. It is demonstrated that wall interactions have a strong effect on the dynamic phase boundaries and stresslet. We finish by discussing the effect of thermal fluctuations and strategies of performing Brownian dynamics for the vesicle system. [Preview Abstract] |
Tuesday, November 23, 2010 3:31PM - 3:44PM |
RK.00003: Dynamics of a compound vesicle: analytical modeling Yuan-Nan Young, Shravan Veerapaneni, Jerzy Blawzdziewicz, Petia Vlahovska Extensive work, both numerical simulations and analytical modeling, on these dynamics provide insights to understanding the suspension phenomena of vesicles in experiments. Recently, they have been used as a multi-functional platform for drug-delivery. In this work the dynamics of such compound vesicles is investigated analytically using the small-deformation method. Results show that for a vesicle enclosing a rigid particle in a simple shear flow, transition from tank-treading to tumbling is possible even in the absence of viscosity mismatch in the interior and exterior fluids. Comparison with results from numerical simulations will be presented, and the rheology of suspension of such compound vesicles will be discussed. [Preview Abstract] |
Tuesday, November 23, 2010 3:44PM - 3:57PM |
RK.00004: Dynamics of a compound vesicle: numerical simulations Shravan Veerapaneni, Yuan-Nan Young, Petia Vlahovska, Jerzy Blawzdziewicz Vesicles (self-enclosing lipid membranes) in simple linear flows are known to exhibit rich dynamics such as tank-treading, tumbling, trembling (swinging), and vacillating breathing. Recently, vesicles have been used as a multi-functional platform for drug-delivery. In this work, the dynamics of simplified models for such compound vesicles is investigated numerically using a state-of-the-art boundary-integral code that has been validated with high accuracy and efficiency. Results show that for a vesicle enclosing a rigid particle in a simple shear flow, transition from tank-treading to tumbling is possible even in the absence of viscosity mismatch in the interior and exterior fluids. We will discuss the shape transformations, multiple particle interactions and the flow properties. Comparison with results from analytical modeling gives insights to the underlying physics for such novel dynamics. [Preview Abstract] |
Tuesday, November 23, 2010 3:57PM - 4:10PM |
RK.00005: Lattice-Boltzmann simulation of a confined tank-treading vesicle under shear Badr Kaoui, Jens Harting, Chaouqi Misbah Dynamics of a vesicle under shear flow between two parallel plates is studied using lattice-Boltzmann simulations. We first present how we adapted the lattice-Boltzmann method to simulate vesicle dynamics basing on the same approach as the one used in the immersed boundary method. The fluid flow is computed on an Eulerian regular fixed mesh while the location of the vesicle membrane is tracked by a Lagrangian moving mesh. As benchmarking tests, the known vesicle equilibrium shapes in a fluid at rest are found and the dynamical behavior of a vesicle under simple shear flow is being reproduced. Further, we focus on investigating the effect of confinement on the dynamics. In particular we study how the vesicle's steady inclination angle in the tank-treading regime depends on the degree of confinement (the ratio of the effective radius of the vesicle to the half height of the channel). The effective viscosity of the fluid, in the presence of the vesicle, is also measured and the influence of the confinement on it is analysed. Both the inclination angle and the membrane tank-treading velocity are found to decrease with increasing confinement. [Preview Abstract] |
Tuesday, November 23, 2010 4:10PM - 4:23PM |
RK.00006: Reynolds number effects on the behavior of lipid vesicles David Salac, Michael Miksis For lipid vesicles to be of general use, such as drug delivery systems, the behavior of vesicles in different flow conditions must be understood. Currently most investigations into lipid vesicles are restricted to the creeping regime. Here a new 4-step Navier-Stokes solver coupled to a level set scheme is used to numerically investigate the behavior of lipid vesicles in non-zero Reynolds number flow regimes. Results show that the behavior of lipid vesicles is highly dependent on the Reynolds number. For example, we have observed that a vesicle which tumbles in the Stokes regime will revert back to tank-treading as inertial effects increase. Here the numerical method will be briefly outlined and the influence of the Reynolds number on the behavior of lipid vesicles will be presented. [Preview Abstract] |
Tuesday, November 23, 2010 4:23PM - 4:36PM |
RK.00007: Gravity Induced Sedimentation of Giant Lipid Vesicles Andres Gonzalez-Mancera, Ivan Rey Suarez, Chad Leidy The mechanical properties of the lipid bilayer influence the gravity-induced sedimentation of vesicles toward a horizontal surface. In this work, the sedimentation rate and strain of lipid vesicles is studied using computational simulations performed using an algorithm based on the boundary element method. The mechanical behavior of the lipid bilayer is modeled considering two modes of deformation responsible for increases in area strain. The first is the smoothing of suboptical thermal undulations and the second is the direct stretching of the area per lipid molecule. Properties of the lipid bilayer are controlled by adjusting its bending and area compressibility moduli. The electrostatic interaction between the sedimenting vesicle and the glass surface is also considered in order to improve agreement with our experimental measurements. We use the linear Deryaguin approximation, which takes into account ionic screening, to calculate the electrostatic repulsive interaction between the glass surface and the charged vesicle. The algorithm shows good agreement with experimental results for both the sedimentation rate and vesicle deformation at equilibrium. [Preview Abstract] |
Tuesday, November 23, 2010 4:36PM - 4:49PM |
RK.00008: The effect of the electrical double layer on the membrane charging process Miao Yu, Hao Lin The electrical charging process of a lipid membrane immersed in electrolytic solutions is of significance to a variety of applications including electroporation and electrodeformation. In these phenomena, the build-up of a potential difference across the membrane (the so-called transmembrane potential, or TMP) induces pore formation and membrane permeabilization (in electroporation) or deformation (in electrodeformation). The classical model treats the membrane as an equivalent capacitor-resistor system which is valid in the zero-thickness electrical double layer (EDL) limit. In this work, the effects of a finite EDL on the charging dynamics are investigated. Starting from the Nernst-Planck equations governing ionic transport, the membrane charging problem is solved in both planar and spherical geometries, and using both analytical and numerical methods. The results demonstrate that the effects of the EDL become more significant as the electrical conductivity of the electrolytic solution decreases, which is a natural consequence of an increased Debye length. The steric effect, which often arises in the limit of large zeta-potentials, is shown to be insignificant for physiological applications. The effective circuit equivalence of the EDL is calculated and validated. The results are discussed in comparison with experimental data on electroporation from the literature. [Preview Abstract] |
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