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 H23: Biofluids: Squirmers, Cilia and Pumping |
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Chair: Shahrzad Yazdi, Pennsylvania State University Room: 300 |
Monday, November 23, 2015 10:35AM - 10:48AM |
H23.00001: Locomotion of spherical squirmers in a viscoelastic fluid near a planar interface Shahrzad Yazdi, Ali Borhan In an attempt to better understand the confined swimming of a microorganism in a viscoelastic fluid, we have analytically studied the time-averaged locomotion of a spherical squirmer with a reciprocal surface motion near a plane interface in a polymeric solution. The results are presented through a phase-portrait in the swimming orientation and distance from the interface. The ratio of viscosities of the two phases adjacent to the plane interface is varied to examine motion near different types of boundaries. Our analysis shows that the near-wall attraction layer previously reported for a 2D squirmer no longer exists for spherical pullers and pushers. However, the presence of a stable node attracts the swimmer to the vicinity of the wall. [Preview Abstract] |
Monday, November 23, 2015 10:48AM - 11:01AM |
H23.00002: Deformable micro torque swimmer Takuji Ishikawa, Tomoyuki Tanaka, Toshihiro Omori, Yohsuke Imai We investigated the deformation of a ciliate swimming freely in a fluid otherwise at rest. The cell body was modeled as a capsule with a hyper elastic membrane enclosing Newtonian fluid. Thrust forces due to the ciliary beat were modeled as torques distributed above the cell body. Effects of the membrane elasticity, the aspect ratio of cell's reference shape and the density difference between the cell and the surrounding fluid were investigated. The results showed that the cell deformed like heart shape when Capillary number (Ca) was sufficiently large, and the swimming velocity decreased as Ca was increased. The gravity effect on the membrane tension suggested that the upwards and downwards swimming velocities of \emph{Paramecium} might be reglated by the calcium ion channels distributed locally around the anterior end. Moreover, the gravity induced deformation made a cell directed vertically downwards, which resulted in a positive geotaxis like behavior with physical origin. These results are important to understand physiology of ciliate's biological responses to mechanical stimuli. [Preview Abstract] |
Monday, November 23, 2015 11:01AM - 11:14AM |
H23.00003: Optimal computational methods for swimming and pumping with helical filaments at low Reynolds number James Martindale, Mehdi Jabbarzadeh, Henry Fu The flows induced by biological and artificial helical filaments are important to many possible applications including microscale swimming and pumping. Microscale helices can span a wide range of geometries, from thin bacterial flagella to thick helical bacterial cell bodies. While the proper choice of numerical method is critical for obtaining accurate results, there is little guidance about which method is optimal for a specified filament geometry. Using two physical scenarios - a swimmer with a head, and a pump - I establish guidelines for the choice of numerical method based on helical geometry. For a range of helical geometries that encompass most natural and artificial helices, I create benchmark results using a surface distribution of regularized Stokeslets, then evaluate the accuracy of resistive force theory, slender body theory, and a centerline distribution of regularized Stokeslets. Taking the computational cost of each method into account, I present the optimal choice of numerical method for each filament geometry as a guideline for future investigations involving filament-induced flows. [Preview Abstract] |
Monday, November 23, 2015 11:14AM - 11:27AM |
H23.00004: Geometric pumping in autophoretic channels Sebastien Michelin, Thomas Montenegro Johnson, Gabriele De Canio, Nicolas Lobatto-Dauzier, Eric Lauga Pumping at the microscale has important applications from biological fluid handling to lab-on-a-chip systems. It can be achieved either from a global (e.g. imposed pressure gradient) or local forcing (e.g. ciliary pumping). Phoretic slip flows generated from concentration or temperature gradients are examples of such local flow forcing. Autophoresis is currently receiving much attention for the design of self-propelled particles achieving force- and torque-free locomotion by combining two essential surface properties: (i) an activity that modifies the solute content of the particle's environment (e.g. catalytic reaction or solute release), and (ii) a mobility that generates a slip flow from the resulting local concentration gradients. Recent work showed that geometric asymmetry is sufficient for a chemically-homogeneous particle to self-propel. Here we extend this idea to micro-pumping in active channels whose walls possess both chemical activity and phoretic mobility. Using a combination of theoretical analysis and numerical simulations, we show that geometrically-asymmetric but chemically-homogeneous channels can generate pumping and analyze the resulting flow patterns. [Preview Abstract] |
Monday, November 23, 2015 11:27AM - 11:40AM |
H23.00005: Flow Induced by Bacterial Carpets and Transport of Microscale Loads Amy Buchmann, Lisa Fauci, Karin Leiderman, Eva Strawbridge, Longhua Zhao Microfluidic devices carry very small volumes of liquid though channels and may be used to gain insight into many biological applications including drug delivery and development. In many microfluidic experiments, it would be useful to mix the fluid within the chamber. However, the traditional methods of mixing and pumping at large length scales don't work at small length scales. Experimental work has suggested that the flagella of bacteria may be used as motors in microfluidic devices by creating a bacterial carpet. Mathematical modeling can be used to investigate this idea and to quantify flow induced by bacterial carpets. We simulate flow induced by bacterial carpets using the method of regularized Stokeslets, and also examine the transport of vesicles of finite size by arrays of rotating flagella. [Preview Abstract] |
Monday, November 23, 2015 11:40AM - 11:53AM |
H23.00006: Squirming through shear thinning fluids Charu Datt, Lailai Zhu, Gwynn J. Elfring, On Shun Pak Many microorganisms find themselves surrounded by fluids which are non-Newtonian in nature; human spermatozoa in female reproductive tract and motile bacteria in mucosa of animals are common examples. These biological fluids can display shear-thinning rheology whose effects on the locomotion of microorganisms remain largely unexplored. Here we study the self-propulsion of a squirmer in shear-thinning fluids described by the Carreau-Yasuda model. The squirmer undergoes surface distortions and utilizes apparent slip-velocities around its surface to swim through a fluid medium. In this talk, we will discuss how the nonlinear rheological properties of a shear-thinning fluid affect the propulsion of a swimmer compared with swimming in Newtonian fluids. [Preview Abstract] |
Monday, November 23, 2015 11:53AM - 12:06PM |
H23.00007: Squirming propulsion in viscoelastic fluids Marco De Corato, Francesco Greco, Pier Luca Maffettone The locomotion of organisms in Newtonian fluids at low-Reynolds numbers displays very different features from that at large Reynolds numbers; indeed, in this regime the viscous forces are dominant over the inertial ones and propulsion is possible only with non-time-reversible swimming strokes. In many situations of biological interest, however, small organisms are propelling themselves through non-Newtonian fluids such as mucus or biofilms, which display highly viscoelastic properties. Fluid viscoelasticity affects in a complex way both the micro-organisms' swimming velocity and dissipated power, possibly affecting their collective behavior. In our work, we employ the so called ``squirmer'' model to study the motion of spherical ciliated organisms in a viscoelastic fluid. We derive analytical formulas for the squirmer swimming velocity and dissipated power that show a complex interplay between the fluid constitutive behavior and the propulsion mechanism. [Preview Abstract] |
Monday, November 23, 2015 12:06PM - 12:19PM |
H23.00008: Self-propulsive motion and deformation of a chemically-driven drop. Natsuhiko Yoshinaga Spontaneous motion has attracted lots of attention in the last decades in fluid dynamics for its potential application to biological problems such as cell motility. Recently, several model experiments showing spontaneous motion have been proposed and revealed the underlying mechanism of the motion. The systems in these works consist of relatively simple ingredients, but nevertheless their motion and deformation give us an impression as if they are alive. Importantly, the system breaks symmetry and chooses one direction of motion. We theoretically derive a set of nonlinear equations exhibiting a transition between stationary and motile states starting from advection-reaction-diffusion equation driven away from an equilibrium state due to chemical reactions. A particular focus is on how hydrodynamic flow destabilizes an isotropic distribution of a concentration field. We also discuss a shape of the droplet. Due to self-propulsive motion and flow around the droplet, a spherical shape becomes unstable and it elongates perpendicular to the direction of motion. This fact would imply that the self-propulsion driven by chemical reaction is characterized as a pusher in terms of a flow field. We shall also show numerical results using the phase field model. [Preview Abstract] |
Monday, November 23, 2015 12:19PM - 12:32PM |
H23.00009: Ciliary fluid transport enhanced by viscoelastic fluid Hanliang Guo, Eva Kanso Motile cilia encounter complex, non-Newtonian fluids as they beat to gain self-propulsion of cells, transport fluids, and mix particles. Recently there have been many studies on swimming in complex fluids, both experimentally and theoretically. However the role of the non-Newtonian fluid in the ciliary transport system remains largely unknown. Here we use a one-way-coupled immersed boundary method to evaluate the impacts of viscoelastic fluid (Oldroyd-B fluid) on the fluid transport generated by an array of rabbit tracheal cilia beating in a channel at low Reynolds number. Our results show that the viscoelasticity could enhance the fluid transport generated by the rabbit tracheal cilia beating pattern and the flow is sensitive to the Deborah number in the range we investigate. [Preview Abstract] |
Monday, November 23, 2015 12:32PM - 12:45PM |
H23.00010: Beyond the mucus escalator: Complex ciliary hydrodynamics in disease and function Janna Nawroth, Hanliang Guo, Dabiri John, Eva Kanso, Margaret McFall-Ngai Cilia are microscopic, hair-like structures lining external and internal body surfaces where they interact with fluids. The main function of motile cilia is often described as that of a ``mucus escalator'', i.e., a homogeneous ciliary carpet moving along layer of mucus along the surface to transport food, germ cells, debris, or pathogens. Accordingly, the performance of ciliary systems is usually measured in terms of a single metric, transport velocity, or its presumed proxy, ciliary beat frequency. We challenge this simple view through the observation that both healthy and diseased biological systems exhibit a variety of cilia morphologies, beat patterns, and arrangements, resulting in complex flow patterns and transport phenomena that cannot be reduced to a single parameter. Here we present two case studies. In one system, the ciliated surface creates two distinct flow regimes for first trapping and then sheltering potential symbiont bacteria for further biochemical screening. In the other system, chronic disease induces a misalignment of ciliary beat, leading to a pathological transition from uniform mucus transport to a pattern of stagnation and circulation. These studies suggest that (a), we need to develop a wider range of metrics for describing ciliary transport in biological and clinical contexts, and (b), engineered ciliated systems exploiting a variety of design parameters could provide novel ways of manipulating fluids at the microscale. [Preview Abstract] |
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