Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session H12: Swimming, Motility and Locomotion |
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Sponsoring Units: DFD GSNP Chair: Jay Tang, Brown University Room: 271 |
Tuesday, March 14, 2017 2:30PM - 2:42PM |
H12.00001: Spontaneous and induced gait-switching in microswimmers Kirsty Y. Wan, Raymond E. Goldstein Self-propulsion by slender structures known as cilia and flagella can present a significant selective advantage. Great variability exists in the number of flagella, their beating modes, and greater still in the basal architecture whence the flagella emanate. In species of enteric bacteria, flagella bundle coherently behind a rod-shaped cell to push the organism forward, while the model alga C. reinhardtii uses two near-identical flagella to pull itself through the fluid, executing a breaststroke. In reality, neither gait is stereotypical. For free-living unicellular eukaryotes with few flagella the question of their actuation and coordination has been receiving growing attention from theorists and experimentalists alike. Performing a comparative study across select flagellates, we demonstrate an unprecedented diversity in swimming gaits and reveal the extent to which control of flagellar motility is driven intracellularly. Stochastic bifurcations between different modes of swimming are visualised at high spatiotemporal resolution, and dynamic changes in flagellar beating shown to elicit in trajectory reorientation and responsive navigation. These insights suggest that fast transduction of signal to peripheral appendages may have evolved far earlier than previously thought. [Preview Abstract] |
Tuesday, March 14, 2017 2:42PM - 2:54PM |
H12.00002: Entrainment and capture by swimming cells Arnold Mathijssen, Raphael Jeanneret, Marco Polin Floating particles that collide with a micro-swimmer can be entrained for long distances (Jeanneret et al., Nat. Comm. 7: 12518, 2016), which provides an opportunity for numerous biological processes to occur with prolonged contact times, including the capture of nutrients and virus infection. Here, we show that the entrainment mechanism is universal for different organisms, C. reinhardtii, T. subcordiforms and O. marina, regardless of diversity in propulsion mechanism and hydrodynamic signature. The flows generated near these microbes are simulated throughout the swimming stroke, and the resulting entrainment lengths compared with our experiments. We find a series of compromises: Flagella can reduce contact times with less tidy interactions, but the entrainment frequency increases as flagella pull particles towards the body. The contact time grows quadratically with swimmer size, but decreases with swimming speed or encounter rate. With the inclusion of Brownian noise, there is an optimal particle size for each swimmer and, conversely, there is an optimal organism for each floating object. We analyse the features of the entrainment mechanism with a Taylor-dispersion theory, and demonstrate how the presented trade-offs may be tuned quantitatively in various biological situations. [Preview Abstract] |
Tuesday, March 14, 2017 2:54PM - 3:06PM |
H12.00003: Swimming Pattern of \textit{Vorticella convallaria} Trophont in the Hele-Shaw Confinements Younggil Park, Sangjin Ryu, Sunghwan Jung In the trophont form \textit{Vorticella convallaria }is a sessile stalked ciliate, which consists of an inverted bell-shaped cell body (zooid) and a slender stalk attaching the zooid to a substrate. Under mechanical shearing, the zooid is separated from the stalk and can swim using circular cilia rows around the oral part. Here we present how the stalkless trophont zooid of \textit{V. convallaria }swims in Hele-Shaw geometries, as a model system for microorganism swimming. After having harvested stalkless zooids, we observed their swimming in water between two glass surfaces with narrow gaps using video microscopy. Based on their swimming trajectories measured with image analysis, we investigated how the swimming pattern of the trophont zooid of \textit{V. convallaria} was influenced by the constraints. [Preview Abstract] |
Tuesday, March 14, 2017 3:06PM - 3:18PM |
H12.00004: Modeling the enhancement of the swimming speed of flagellated bacteria in polymer solutions Jay X. Tang, Xuejun Zhang, Fangfu Ye, William Klimpert, Robert Pelcovits The swimming speed of many species of flagellated bacteria initially increases and then decreases as a function of the viscosity of the medium, which is varied by the addition of high molecular weight polymers. An earlier model accounts for such a peaked distribution (Magariyama & Kudo, Biophys J, 2012), but it was recently shown to give rise to incorrect predictions for the cell body rotation rate (Martinez et al., PNAS, 2014). The authors of the latter work suggested that low-molecular weight impurities from the added polymers account for the peaked speed-viscosity curves in some cases. We measured the swimming speed of a uni-flagellated bacterium, caulobacter crescentus, in solutions of a number of polymers of several different sizes. Our findings confirm the peaked speed-viscosity curve for each of several distinct polymers added, suggesting that the general behavior is highly unlikely due to impurities. We propose a modification of the models used by the previous investigators in order to better explain our new experimental results. We have also performed numerical calculations based on the modified model to show that it properly accounts for the experimental results. [Preview Abstract] |
Tuesday, March 14, 2017 3:18PM - 3:30PM |
H12.00005: How cells jump: Ultrafast motions in the single-celled micro-organism Halteria grandinella Deepak Krishnamurthy, Fabien Cockenpot, Manu Prakash Here we describe a novel behavior of "jumping" in micro-organisms, observed in the common freshwater ciliate Halteria grandinella. This organism’s swimming motion is characterized by periods of forward swimming at around 10 body lengths/s punctuated by extremely rapid backward "jumps" where the organism reaches speeds of more than 150 body lengths/s. We show, using detailed measurements of the swimming motion through high-speed video microscopy, that the extreme swimming speeds are achieved by the motile cilia transitioning to a beating mode characterized by a significantly larger beat amplitude and an associated reversal in the direction of thrust production. We further show that H.grandinella cells can sense a fluid shear stress signal and "jump" in response: a possible predator avoidance mechanism. We investigate this mechanism of shear sensing and study the role of the long, slender structures known as "cirri" as microscale sensors of shear stress. The jumping of H.grandinella is at the limits of the metabolic rate of the organism and thus offers insights into the limiting factors governing energy storage and mechanical power release at the microscale. Concurrently their sensing apparatus allows an understanding of the physical limits of microscale mechanical sensing. [Preview Abstract] |
(Author Not Attending)
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H12.00006: Polymer dynamics driven by a helical filament Andrew Balin, Tyler Shendruk, Andreas Zoettl, Julia Yeomans Microbial flagellates typically inhabit complex suspensions of extracellular polymeric material which can impact the swimming speed of motile microbes, filter-feeding of sessile cells, and the generation of biofilms. There is currently a need to better understand how the fundamental dynamics of polymers near active cells or flagella impacts these various phenomena. We study the hydrodynamic and steric influence of a rotating helical filament on suspended polymers using Stokesian Dynamics simulations. Our results show that as a stationary rotating helix pumps fluid along its long axis, nearby polymers migrate radially inwards and are elongated in the process. We observe that the actuation of the helix tends to \emph{increase} the probability of finding polymeric material within its pervaded volume. At larger Weissenberg numbers, this accumulation of polymers within the vicinity of the helix is greater. Further, we have analysed the stochastic work performed by the helix on the polymers and we show that this quantity is positive on average and increases with polymer contour length. Our results provide a basis for understanding the microscopic interactions that govern cell dynamics in complex media. [Preview Abstract] |
Tuesday, March 14, 2017 3:42PM - 3:54PM |
H12.00007: Realization of the Najafi-Golestanian microswimmer Maxime Hubert, Galien Grosjean, Guillaume Lagubeau, Nicolas Vandewalle The development of artificial microswimmers, microscopic robots that swim in a fluid like sperm cells and motile bacteria, could cause a leap forward in various fields such as microfluidics, microsystems, or minimally invasive medicine. Nature provides plenty of examples of efficient microswimmers. However, a bottom-up approach, looking at the simplest ingredients needed to generate a microswimmer, can lead to a deeper understanding of the swimming problem. First described by Najafi and Golestanian\footnote{A. Najafi and R. Golestanian, Phys. Rev. E 69, 062901 (2004)}, a paradigmatic microswimmer is the three-linked-spheres model, which follows a minimalist approach for propulsion by shape shifting. In this presentation, we describe the experimental realisation of this microswimmer using self-assembled ferromagnetic particle at an air-water interface, powered by an uniform oscillating magnetic field\footnote{G. Grosjean, M. Hubert, G. Lagubeau, and N. Vandewalle, Phys. Rev. E 94, 021101(R)}. A model, using two harmonic oscillators, reproduces the experimental findings. Because the model remains general, the same approach could be used to design a variety of efficient microswimmers. [Preview Abstract] |
Tuesday, March 14, 2017 3:54PM - 4:06PM |
H12.00008: The physics of the unconventional motility strategy of euglenids Marino Arroyo, Giovanni Noselli, Antonio DeSimone Euglenids are a family of unicellular protists, which use flagella to move in a fluid. However, they are also capable of performing elegantly concerted large amplitude deformations of the cell shape, in what is known as metaboly. To perform metaboly, euglenids use an elaborate cortical complex capable of actively imposing spatially modulated shear deformations on the cell surface. This mode of cell deformation has been linked to motility, but biophysical studies have demonstrated that it leads to very small swimming velocities as compared to flagellar locomotion. Furthermore, why would these cells possess two elaborate apparatus for the same function remains unclear. In this work, we combine experimental observations of euglena gracilis cells with theoretical models to shed light into the function of metaboly. The theoretical models account for the force generation and shape evolution at the cell envelop, together with the mechanical interaction of the cell with its environment. We characterize the efficiency of the two modes of locomotion of this cells in terms of the physical nature of their environment. [Preview Abstract] |
Tuesday, March 14, 2017 4:06PM - 4:18PM |
H12.00009: Bubble-based acoustic swimmers: a dual micro/macro-fluidics study Nicolas Bertin, Tamsin Spelman, Olivier Stéphan, Eric Lauga, Philippe Marmottant Without protection, a micron-sized free air bubble at room temperature in water has a life duration shorter than a few tens of seconds. Using two-photon lithography, which is similar to 3D printing at the micron scale, we can build "armors" for these bubbles: micro-capsules with an opening. These armors contain the bubble and extend its lifespan to several hours in biological buffer solutions. When excited by an external ultrasonic wave, the bubble performs large amplitude oscillations at the capsule opening and generates a powerful acoustic streaming flow (velocity up to dozens of mm/s). We show how to obtain blood-vessel-sized acoustic swimmers for drug-delivery applications. They contain multiple capsules of different aperture sizes: this makes them resonant at different frequencies. By adjusting the frequency, we can adjust the swimming direction. A micro/macro parallel study is also performed. On one hand, we study microswimmers on the 20-50 µm scale: propulsion forces are measured and predicted. On the other hand, we study macroscopic "milliswimmers" containing bubbles that are 2 to 10 mm in diameter, allowing us to understand in detail the modes of vibration, to quantitatively predict the swimming motions and inspire new designs for microswimmers. [Preview Abstract] |
Tuesday, March 14, 2017 4:18PM - 4:30PM |
H12.00010: Self-assembled surface swimmers and micromanipulators Galien Grosjean, Maxime Hubert, Guillaume Lagubeau, Nicolas Vandewalle Soft magnetic particles floating on a liquid can spontaneously assemble into ordered structures.\footnote{N.Vandewalle \emph{et al.}, Phys. Rev. E {\bf 85}, 041402 (2012)} This process is controlled through the amplitude and orientation of an external magnetic induction field. Complex behaviors can arise under a time-dependent magnetic field.\footnote{G. Lagubeau \emph{et al.}, Phys. Rev. E {\bf 93}, 053117 (2016)} In particular, assemblies of three particles or more can undergo deformations in non-time-reversible sequences, a necessary condition for low Reynolds number locomotion.\footnote{G. Grosjean \emph{et al.}, Phys. Rev. E {\bf 94}, 021101(R) (2016)} Such microswimmers can follow precisely controlled trajectories.\footnote{G. Grosjean \emph{et al.}, Sci. Rep. {\bf 5}, 16035 (2015)} As a consequence, these self-assembled structures can be used as microrobots to perform different tasks, such as the capture, transport and release of a microcargo, the mixing of fluids at low Reynolds number, and more. [Preview Abstract] |
Tuesday, March 14, 2017 4:30PM - 4:42PM |
H12.00011: A self-propelled two-sphere swimmer Shannon Jones, Amneet Bhalla, Boyce Griffith, Daphne Klotsa We use the immersed boundary method to study an internally-vibrated swimmer composed of two unequal sized spheres connected by a spring at intermediate Reynolds numbers (1-100). Because the two-sphere swimmer has a reciprocal stroke, it does not swim in the Stokes regime; however, due to its asymmetry, it swims at larger Reynolds numbers. We find that the two-sphere swimmer remains stationary or swims depending on the parameters (amplitude, frequency, sphere diameter and distance, and Reynolds number). An unexpected observation is that the direction of swimming also depends on the parameters: the swimmer moves either in the direction of the large sphere or the direction of the small sphere under different conditions. [Preview Abstract] |
Tuesday, March 14, 2017 4:42PM - 4:54PM |
H12.00012: Fission and fusion scenarios for magnetic microswimmer clusters Andreas Kaiser, Francisca Guzman-Lastra, Hartmut Lowen Fission and fusion processes of particles clusters occur in many areasof physics and chemistry from subnuclear to astronomic length scales. Here we study fission and fusion of magnetic microswimmer clusters as governed by their hydrodynamic and dipolar interactions. Rich scenarios are found which depend crucially on whether the swimmer is a pusher or a puller. A linear magnetic chain of pullers is stable while a pusher chain shows a cascade of fission processes as the self-propulsion velocity is increased. Contrarily, magnetic ring clusters show fission for any type of swimmer. Moreover, we find a plethora of possible fusion scenarios if a single swimmer collides with a ringlike cluster and two rings spontaneously collide. [Preview Abstract] |
Tuesday, March 14, 2017 4:54PM - 5:06PM |
H12.00013: Ellipsoidal Brownian self-driven particles in a magnetic field Mario Sandoval, Fan Wai-Tong, On Shun Pak We study the two-dimensional Brownian dynamics of an ellipsoidal paramagnetic microswimmer moving at low Reynolds number and subject to a magnetic field. Its corresponding mean-square displacement showing the effect of particles’s shape, activity, and magnetic field on the microswimmer’s diffusion is analytically obtained. A comparison among analytical and computational results is also made and we obtain good agreement. Additionally, the effect of self-propulsion on the transition time from anisotropic to isotropic diffusion of the ellipse is also elucidated. [Preview Abstract] |
Tuesday, March 14, 2017 5:06PM - 5:18PM |
H12.00014: Convective self-propulsion of catalytic particles Oleg Shklyaev, Henry Shum, Anna Balazs A mechanism for the self-propulsion of particles by transduction of chemical energy into convective motion of the host fluid is proposed. The convection is driven by the fluid density variation created around active particles uniformly coated with a catalyst that decomposes a reagent present in the solution. Active particles and passive particles, which are not coated with catalyst, initially dispersed throughout the container are assembled into clusters by the fluid flow. The fluid dynamics are modelled via a lattice-Boltzmann approach and interactions with solid particles through the immersed boundary method. Depending on the configuration and composition of the cluster, the geometry of the container, and the chemical reaction considered, the mobile clusters can translate, spin, or remain stationary. [Preview Abstract] |
Tuesday, March 14, 2017 5:18PM - 5:30PM |
H12.00015: Spontaneous rotation of a melting ice disk stephane dorbolo, nicolas vandewalle, baptiste darbois-texier Ice disks were released at the surface of a thermalised aluminium plate. The fusion of the ice creates a lubrication film between the ice disk and the plate. The situation is similar to the Leidenfrost effect reported for liquid droplet evaporating at the surface of a plate which temperature is above the boiling temperature of the liquid. An analogy is depicted between the Leidenfrost phenomenon and the rapid fusion of a solid at the contact of a hot plate. Similarly to Leidenfrost droplet, we observe that, while the ice disks were melting, the disks were very mobile: translation and rotation. [Preview Abstract] |
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