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 M29: Biofluids: Cellular V: Complex Interactions |
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Chair: Michael Shelley, Courant Institute of Mathematical Sciences, NYU Room: Ballroom III |
Tuesday, November 22, 2011 8:00AM - 8:13AM |
M29.00001: Effect of physical variables on capture of magnetic nanoparticles in simulated blood vessels Minghui Zhang, Christopher Brazel This study investigated how the percent capture of magnetic nanoparticles in a simulated vessel varies with physical variables. Magnetic nanoparticles (MNPs) can used as part of therapeutic or diagnostic materials for cancer patients. By capturing these devices with a magnetic field, the particles can be concentrated in an area of diseased tissue. In this study, flow of nanoparticles in simulated blood vessels was used to determine the affect of applying an external magnetic field. This study used maghemite nanoparticles as the MNPs and either water or Fetal Bovine Serum as the carrier fluid. A UV-Vis collected capture data. The percent capture of MNPs was positively influenced by five physical variables: larger vessel diameters, lower linear flow velocity, higher magnetic field strength, better dispersion, lower MNP concentration, and lower protein content in fluid. Free MNPs were also compared to micelles, with the free particles having more successful magnetic capture. Four factors contributed to these trends: the strength of the magnetic field's influence on the MNPs, the MNPs' interactions with other particles and the fluid, the momentum of the nanoparticles, and magnetic mass to total mass ratio of the flowing particles. [Preview Abstract] |
Tuesday, November 22, 2011 8:13AM - 8:26AM |
M29.00002: Viscoelastic Response of Cytoskeleton: Prestress effect Len Pismen, Konstantin Morosov, Marco Salm The differential elastic modulus of an active actomyosin network is computed as a function of applied stress, taking into account both thermal and motor contributions to filament compliance in the low-frequency domain. It is shown that, due to a dual nature of motors activity, increasing motor concentration may either stiffen the network due to stronger prestress or soften it due to motor agitation, in accordance with experimental data. Prestress anisotropy, which may be induced by redistribution of motors triggered by external force, causes anisotropy of elastic moduli. This helps to explain contradictory phenomena of cell fluidization and resolidification in response to transient stretch. Reshaping of epithelial cells is modeled by allowing for prestress anisotropy due to myosin redistribution. [Preview Abstract] |
Tuesday, November 22, 2011 8:26AM - 8:39AM |
M29.00003: Numerical study on the initial stage of thrombus growth Shu Takagi, Satoshi Ii, Seiji Shiozaki, Kazuyasu Sugiyama, Yoichiro Matsumoto Thrombosis is regarded as one of the most important diseases, which cause the myocardial and cerebral infarctions. It is affected from molecular scale protein-protein interaction to continuum scale in blood flow. Initially, platelets start aggregate at the injured vessel wall, where von Willebrand Factor (vWF) is attached. The Glycoprotein, GPIb-$\alpha {\rm s}$ on platelet membrane starts showing ligand-receptor interaction with this vWF and platelets start aggregating around this spot. In the present study, the molecular scale interaction between vWF and GPIb-$\alpha \quad {\rm g}$ is taken into account through the kinetic Monte Carlo simulations. Then, the interacting force between platelets and vascular endothelium obtained from kinetic Monte Carlo simulation is coupled with the continuum scale simulation. The results illustrate that platelets are much easier to aggregate on the wall in the presence of red blood cells and the effect of molecular interaction force are quantitatively discussed on the aggregation of platelets. [Preview Abstract] |
Tuesday, November 22, 2011 8:39AM - 8:52AM |
M29.00004: Diamagnetic Cell Focusing in Ferrofluid Microchannel Flows Jian Zeng, Litao Liang, Tzuen-Rong Tzeng, Xiangchun Xuan Focusing cells into a tight stream is usually a necessary step prior to counting, detecting, and sorting them. It has been achieved by using either sheath flow(s) to pinch the cellular stream or force(s) to manipulate the suspended cells directly. In this talk we present a three-dimensional magnetic cell focusing method in ferrofluid flow through a rectangular microchannel. A pair of facing permanent magnets is embedded into the chip to create a magnetic field null inside the microchannel. Diamagnetic cells experience negative magnetophoresis in a more magnetizable ferrofluid and thus migrate toward the centerline of the bottom channel wall. The effects of flow rate and ferrofluid concentration on the magnetic focusing of yeast cells in both the horizontal and the vertical planes of the microchannel are examined experimentally. The obtained results are compared with the theoretical predictions of an analytical model. [Preview Abstract] |
Tuesday, November 22, 2011 8:52AM - 9:05AM |
M29.00005: Cellular Dewetting: Opening of Macroapertures in Endothelial Cells David Gonzalez-Rodriguez, Madhavi Maddugoda, Caroline Stefani, Sebastien Janel, Frank Lafont, Damien Cuvelier, Emmanuel Lemichez, Francoise Brochard-Wyart Pathogenic bacteria can cross from blood vessels to host tissues by opening transendothelial cell macroapertures. Here we model the opening of macroapertures as a new form of dewetting, driven by the cell's membrane tension. While liquid dewetting is irreversible, we show that cellular dewetting is transient. Our model predicts the minimum radius for hole nucleation, the maximum hole size, and the dynamics of opening, in good agreement with the experiments. The physical model is then coupled with biological experimental data to reveal that a certain curvature-sensing protein controls the line tension at the rim of the hole and opposes its opening. [Preview Abstract] |
Tuesday, November 22, 2011 9:05AM - 9:18AM |
M29.00006: A stochastic model for DNA electrotransfer with finite pulses Miao Yu, Hao Lin Gene electrotransfer is a non-viral method to introduce foreign DNA into cells using electric fields. The fundamental mechanism for DNA transfer is unknown and under debate. While previous research investigated the role of DNA-membrane interaction and endocytosis, we here explore electrophoresis as a possible mechanism to assist translocation. In this model, DNA strands are treated as long-chain polymers driven through pores on the cell membrane by applied electric fields. A stochastic model is constructed, and solved numerically to parametrically study the time process of DNA translocation. Numerical results indicate that there exists an optimal pulse length beyond which DNA delivery probability no longer increases. The optimal length correlates inversely with applied field strength, and increases nonlinearly with DNA length. The results show good agreement with data from both solid-state nano-pore and electroporation experiments, and suggest that electrophoresis may play a key role in electroporation-mediated gene delivery. [Preview Abstract] |
Tuesday, November 22, 2011 9:18AM - 9:31AM |
M29.00007: Dynamics of a microsphere in an anisotropic gel: a frontier in intracellular microrheology Manuel Gomez-Gonzalez, Juan Carlos del Alamo Particle tracking microrheology (PTM) is widely used to calculate the shear modulus of complex fluids. This technique is specially suitable to characterize the cell cytoplasm but its current formulation assumes isotropy, thereby rendering averaged shear moduli that are affected by the motion of the probe and do not represent accurately the inherent properties of the medium. This leads to errors greater than 100\% when isotropic PTM is applied to live cells. In this work, we modify the PTM formulation to obtain the Directional Shear Moduli of an orthotropic medium. We study the motion of a spherical particle in an orthotropic medium, described by the Leslie-Ericksen equations. We calculate the drag force exerted on the particle, in the general case of 5 independent viscosity coefficients. In the idealized case where only 2 of the viscosity coefficients are important, we obtain a closed form analytical solution that allows us to modify current PTM formulae and obtain the directional shear moduli from the random thermal motion of a particle embedded in the cell cytoplasm. [Preview Abstract] |
Tuesday, November 22, 2011 9:31AM - 9:44AM |
M29.00008: Flow instability and mixing of a complex fluid with extensional microstructure Meredith Betterton, Ang-Sheng Hang, Michael Shelley Several complex fluid systems show extensional dynamics in their microstructural evolution. Examples include isotropic-to-smectic liquid crystal phase transitions, and the relative sliding dynamics of microtubules induced by motor protein activity. To understand the macroscopic dynamics of such a system, we examine a simple kinetic model of a suspension of extending, hydrodynamically-coupled fibers. It is similar in structure to recent theories of motile suspensions. Our stability analysis shows the existence of large-scale flow instabilities, and numerical simulation of the nonlinear kinetic-fluid model shows the development of strongly time-dependent and complex macroscopic flows. [Preview Abstract] |
Tuesday, November 22, 2011 9:44AM - 9:57AM |
M29.00009: Getting trapped in low-Re turbulence and collaborating your way out Enkeleida Lushi, Michael J. Shelley We present an efficient numerical method to compute the dynamics of thousands of self-motile rod-like micro-swimmers that interact directly via the fluid flow they collectively generate. Using this method, we study the dynamics of rod-like swimmer particles in a background cellular vortical flow and show that hydrodynamic and steric interactions, the number of swimmers and system size, as well as the swimming mechanism (``Pusher'' vs. ``Puller''), have an effect on whether the swimmers get trapped in vortices or can escape them. [Preview Abstract] |
Tuesday, November 22, 2011 9:57AM - 10:10AM |
M29.00010: Charge effect on solute transport across a periodic fiber array Masako Sugihara-Seki, Takeshi Akinaga, Hideyuki O-tani The luminal surface of vascular endothelial cells is covered by a fiber matrix layer referred to as the glycocalyx layer, and charge carried by the glycocalyx layer has been shown to significantly modulate the permeability of the microvessel wall to charged solutes. The present study is aimed to develop a fluid mechanical and electrostatic model for the transport of charged solutes across the glycocalyx layer and to examine the charge effect on the rate of diffusional and convectional transport of the solute. The glycocalyx layer was assumed to consist of identical circular cylinders with fixed surface charge, aligned parallel to each other in a hexagonal arrangement. For a spherical solute with fixed surface charge suspended in an electrolyte solution between circular cylinders, fluid mechanical and electrostatic analyses were carried out to calculate the flow field as well as the electric field around the solute to estimate the rate of solute transport across the layer. It was found that even at rather large ion concentrations, the repulsive electrostatic interaction between the solute and cylinder of like charge could significantly reduce the transport rate of the solute. [Preview Abstract] |
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