Bulletin of the American Physical Society
72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13
Saturday–Tuesday, November 23–26, 2019; Seattle, Washington
Session Q31: Biological Fluid Dynamics: Locomotion Cilia |
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Chair: David Saintillan, University of California San Diego Room: 613 |
Tuesday, November 26, 2019 7:45AM - 7:58AM |
Q31.00001: Hydrodynamic synchronization of spontaneously beating filaments David Saintillan, Brato Chakrabarti Cilia and flagella are thin hair-like cellular projections that play a range of crucial roles from propulsion at low Reynolds number to long-range hydrodynamic transport. The movement of the cilium is produced by the bending of its core, known as the axoneme, consisting of 9+2 pairs of microtubules. In presence of ATP, molecular motors connecting microtubules undergo cycles of attachment and detachment and generate sliding forces that are converted to waving motion of the filaments. We present a microscopic model that accounts for the stochastic kinetics of molecular motors and mechanical feedback from the axoneme, and produces spontaneous oscillations consistent with those of sperm, cilia and \emph{Chlamydomonas}. Using this model for the axoneme, we study elastohydrodynamic phase synchronization in a pair of beating filaments. Our computations reveal that symmetric sperm-like beats lead to in-phase synchrony while both in-phase or anti-phase synchrony can emerge for asymmetric ciliary waveforms. We find that phase-synchronization is well captured by a low-dimensional Adler equation and also elucidate the role of biochemical noise in driving phase slips. [Preview Abstract] |
Tuesday, November 26, 2019 7:58AM - 8:11AM |
Q31.00002: Dynamics of a cilium/cilia beating in 3D non-Newtonian flow Chenglei Wang, Simon Gsell, Umberto D'Ortona, Julien Favier Cilia are micro-scale hair-like organelles protruding from the surfaces of eukaryotic cells. Through fluid-structure interaction (FSI), they usually serve for fluid transport and locomotion. Such a FSI problem has been widely explored recently. In most existing works, the fluid is modeled as Newtonian. However, this is not always the case in nature, such as for the airway surface liquid (ASL) covering the epithelial surface of the respiratory system of the human body. In other words, the non-Newtonian flow could play a significant role on the cilia dynamics, which yet has been rarely studied. Therefore, this study aims to bridge this gap. Specifically, the non-Newtonian fluid is described using the power-law model, and each cilium is represented by a flexible filament. A single cilium or an array of cilia are placed in the fluid and driven at their base by a configuration-dependent torque. With a well-established numerical solver based on the immersed boundary lattice Boltzmann method (IBLBM) and the nonlinear finite element method (FEM), the cilia dynamics and their hydrodynamic interactions in the 3D non-Newtonian flow are systematically investigated, and the effects of several key parameters including the power-law index and the cilia spacing are also revealed. [Preview Abstract] |
Tuesday, November 26, 2019 8:11AM - 8:24AM |
Q31.00003: The role of flexibility in sub-inertial swimming: An analysis of millimeter-scale ciliated structures Adrian Herrera-Amaya, Ferhat Karakas, David W. Murphy, Margaret L. Byron Ctenes are rectangular paddle-like structures approximately one millimeter in length, composed of packed bundles of very long cilia. They are used by ctenophores (gelatinous marine zooplankton) to swim at intermediate Reynolds numbers (Re). Using Particle Shadow Velocimetry (PSV), we experimentally examine variations in the beat kinematics and fluid dynamics across ontogeny of the ctenophore Bolinopsis vitrea. In smaller animals, the ctene kinematics resemble the physics of micro-cilia, using spatial asymmetry to produce net thrust. By contrast, the ctenes of larger animals show a decreased spatial asymmetry but maintain the overall thrust by increasing the velocity difference between power and recovery strokes (a strategy which would be ineffective in low Re, time-reversible flows). We also observe wall-normal displacement of the mesoglea which is detectable, nontrivial, and with a frequency approximately equal to that of the ctene beating. Overall, we show that flexibility is a major parameter in ctenophore swimming, and that further study of this system could help elucidate the physics of flexible propulsors at the boundary of the viscous and inertial regimes. [Preview Abstract] |
Tuesday, November 26, 2019 8:24AM - 8:37AM |
Q31.00004: Long-range self-organization of ciliary activity and flow patterns in reconstituted bronchial epithelium Annie Viallat, Etienne Loiseau, simon Gsell, umberto d'ortona, julien favier Mucociliary clearance is the active transport of a complex fluid, mucus, along the airway epithelial surface. Mucus is propelled over tens of centimeters by the beating of billions of active cilia carried by the epithelial ciliated cells. How the necessary coordination of beat directions emerges during ciliogenesis and is maintained is still an open debate. Would the collective motions of ciliary beats involve the dynamics interaction between cilia as observed in long range interaction in active matter systems ? The direction of ciliary beats is constrained by the long-range hydrodynamic forces created by distant cilia and mediated by mucus, and by the planar polarity of the tissue. Here, after highlighting the spontaneous emergence and growth of mucus swirls during ciliogenesis, we show that mucus is necessary to generate and maintain a global swirl, associated with a strong circular directional order of ciliary beats, spanning the whole culture. By showing that large-scale swirl and ciliary order are lost and then recovered by successively removing and adding mucus to the epithelial surface, we demonstrate that the hydrodynamic force exerted locally on each cilium by the mucus flow, itself resulting from the beats of all the cilia of the epithelium, induces its active reorientation. These results are discussed in light of a hydrodynamic model which captures the observed mucus flow patterns. [Preview Abstract] |
Tuesday, November 26, 2019 8:37AM - 8:50AM |
Q31.00005: FAST, NEAREST and Flagellar Regulation Meurig Gallagher, Gemma Cupples, Jackson Kirkman-Brown, David Smith In an age where huge amounts of data can be readily produced it is increasingly important to be able to accurately and efficiently analyse large amounts of data, and to be able to use these analyses as a marker for clinical outcome. However, semen analysis in the human is currently limited to meth- ods such as sperm counting and analysis of fixed cells. To address this, we have developed and released FAST, a free-to-use package for the high-throughput detection and tracking of large numbers of beating flagella in experimental microscopy videos. This new ability to track the detailed flagellar waveform allows for more than just measurements of motility. Alongside FAST we have been developing NEAREST, an open source software enabling the rapid application of a meshless regularised Stokeslet method to solve mobility and resistance problems in Stokes flow. Combining FAST and NEAREST allows for detailed investigation into experimentally intractable quantities such as energy dissipation, disturbance of the surrounding medium and viscous stresses. Finally, we will discuss how the analysis capabilities provided by these tools can be combined, together with models of the elastic behaviour of flagella and learning algorithms to probe the secrets of flagellar regulation in swimming cells. [Preview Abstract] |
Tuesday, November 26, 2019 8:50AM - 9:03AM |
Q31.00006: Modeling the Synchronization of Flagella on the Exterior of a Sphere Karin Leiderman, Forest Mannan, Miika Jarvela Flagella are hair-like appendages attached to microorganisms that allow the organisms to traverse their fluid environment. The algae Volvox are phototactic, spherical swimmers with thousands of biflagellate somatic cells embedded in their surface. Their flagella coordinate their beating, which leads to forward swimming with slight rotations; the coordination of their flagella is not fully understood. In this work, we extend a previously published mathematical model of coordinated flagella on a flat surface to study coordination on the exterior surface of a sphere. The goal was to determine if factors related to~the spherical shape affected flagellar synchronization. Each beating flagella itself is modeled as a small rotating sphere, attached to a point just~above the spherical surface by a spring, and the effects of all other flagella are accounted for with a regularized image system for Stokes flow outside of a sphere. We consider flagellar beating in meridional planes with slight offsets and from the anterior to posterior pole. We found that this minimal model can achieve large-scale coordination of flagella that leads to metachronal waves and also results in velocity fields that represent forward swimming with rotation. We varied parameters for meridional offsets, spring stiffness and number of flagella to study how they each affected the coordination. This study lays the groundwork for future studies to better understand their more complex coordination needed to drive their phototactic behavior. [Preview Abstract] |
Tuesday, November 26, 2019 9:03AM - 9:16AM |
Q31.00007: A computational study of amoeboid motility in 3D: Role of extracellular matrix geometry, cell deformability and cell-matrix adhesion Prosenjit Bagchi, Eric Campbell Cells exhibiting amoeboid locomotion are abundant within the human body, as immune cells, epithelial cells, neuronal cells, embryonic cells, and even metastatic cancer cells migrate using the amoeboid phenotype. Amoeboid locomotion is accomplished through the use of pseudopods, or cylindrical membrane extensions which protrude, bifurcate, and retract dynamically, resulting in a net cell displacement. The modeling of amoeboid locomotion is a complex and multiscale process, where large cell deformation, protein biochemistry, and both cytosolic and extracellular fluid interactions must be considered. Furthermore, cells are often confined inside the extracellular matrix (ECM), a porous, fluid-filled medium. Adhesive interactions between the cell and underlying substrate add further layers of complexity. In this work, we present a 3D computational model of amoeboid migration in various ECM geometries. Our model couples a fluid/structure interaction for extreme cell deformation, a pseudopod generating activator-inhibitor system, cytoplasmic and extracellular fluid motion, and a fully resolved extracellular matrix. Simulation results show a strong coupling between cell deformability, matrix geometry and cell-ECM adhesion providing valuable on the mechanics of amoeboid migration. [Preview Abstract] |
Tuesday, November 26, 2019 9:16AM - 9:29AM |
Q31.00008: Efficient Implementation of Elastohydrodynamic Integral Operators for Stokesian Filaments Atticus Hall-McNair, Thomas Montenegro-Johnson, Hermes Gadêlha, David Smith, Meurig Gallagher Models for simulating the dynamics of flexible biological filaments have historically been mathematically complex and numerically expensive, in part due to numerical stiffness associated with satisfying fiber inextensibility. Moreau et al. (2018) recently demonstrated that a filament could be modeled efficiently by expressing the governing elastohydrodynamic problem via integral equations written in terms of the evolving tangent angle. Combined with a method of lines discretization, the required degrees of freedom for accurate simulation are reduced, alleviating numerical stiffness and enabling efficient computational simulation. In this presentation, I outline recent work which builds upon the Moreau et al. framework, augmenting their formulation with the method of regularized stokeslets of Cortez et al. (2001, 2005) to enable the modeling of non-local hydrodynamic interactions within and between filaments. From this, the non-linear filament deformations caused by shear flows and sedimentation are modeled efficiently, revealing how fiber interactions can lead to geometric buckling instabilities. We also consider the dynamics of active moment driven swimmers for different moment types, and investigate optimal parameter pairings to produce fast swimming in active filaments. [Preview Abstract] |
Tuesday, November 26, 2019 9:29AM - 9:42AM |
Q31.00009: Magnetically powered metachronal waves induce locomotion in capillary self-assemblies Ylona Collard, Galien Grosjean, Nicolas Vandewalle When tiny soft-ferromagnetic particles are placed along a liquid interface and exposed to a vertical magnetic field, the balance between capillary attraction and magnetic repulsion leads to self-organization into well-defined patterns. We demonstrate that precessing magnetic fields induce metachronal waves on the periphery of these assemblies, similar to the ones observed in ciliates and some arthropods. The outermost layer of particles behaves like an array of cilia or legs whose sequential movement causes a net and controllable locomotion. This bioinspired many-particle swimming strategy is effective even at low Reynolds number, using only spatially uniform fields to generate the waves. The motivations for studying these systems range from the fundamental understanding of biological processes to the development of medical and technological applications. [Preview Abstract] |
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