Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session F15: Swimming, Motility, & Locomotion |
Hide Abstracts |
Sponsoring Units: DFD DBIO Chair: Alison Patteson, Syracuse University Room: 210/212 |
Tuesday, March 3, 2020 8:00AM - 8:36AM |
F15.00001: Scattering of a fast-swimming bacterium off of a surface Alexander Petroff, Schuyler Mcdonough, Benjamin Roque The sediment bacterium Thiovulum majus is one of the fastest known |
Tuesday, March 3, 2020 8:36AM - 8:48AM |
F15.00002: Optically-Powered Microscopic Bubble Rockets Samantha Norris, Michael Reynolds, Alejandro Cortese, Paul L McEuen Artificial microswimmers have attracted great interest recently, especially for applications in sensing and biology. In particular, micro-propulsion by producing bubbles using decomposition of a chemical fuel is an attractive method, but it requires a fuel source. In this talk, we demonstrate a new optically-powered approach to catalyst-free bubble self-propulsion that works in a broad range of fluids, including deionized water. These devices, approximately 100 microns in size, consist of encapsulated silicon photodiodes connected in series with two external electrodes. Under standard illumination conditions in a microscope, the photovoltaics drive water splitting at the electrodes and eject the resulting bubbles preferentially in one direction, propelling the device through fluid. These devices are fabricated and released in parallel using standard semiconductor technologies. We discuss the fabrication and characterization of these devices, demonstrate working bubble rockets, and discuss their efficiency and potential applications. |
Tuesday, March 3, 2020 8:48AM - 9:00AM |
F15.00003: Antagonism in multiple-cue chemotaxis in breast cancer cells Soutick Saha, Hye-ran Moon, Bumsoo Han, Andrew Mugler Chemotaxis is defined as biased cell motion towards an external chemical gradient. It is a pivotal step in cancer metastasis where cancer cells move towards chemical cues and spread to different parts of the body. We used triple-negative breast cancer cells to study chemotaxis towards cues formed by multiple growth factors and found, surprisingly, that the bias in the movement was less pronounced when we combine two attractant gradients compared to when we have individual gradients. We study this antagonism using stochastic simulations and a simple analytic model. |
Tuesday, March 3, 2020 9:00AM - 9:12AM |
F15.00004: A universal mechanism for chiral swimming at low Reynolds number Dario Cortese, Kirsty Wan Eukaryotes evolved radically new ways to sense and respond to a constantly changing environment. Even single-celled microorganisms display near-determinstic navigation towards sensory cues. Helical alignment towards gradients is a ubiquitous mechanism by which ciliated and flagellated organisms achieve reorientation in three-dimensional space. This navigational strategy usually requires the presence of a specialised organelle which detects stimulus direction and an about-axis rotation of the organism. Here, we consider the biflagellate green alga Chlamydomonas reinhardtii which has an eyespot photosensor and rotates steadily at 2Hz in the absence of stimuli. We combine theory and experiment to reveal how Chlamydomonas actively modulates asymmetries in flagellar beating to produce axial rotation and steering. In previous models, helical swimming is usually assumed rather than derived. In contrast, in our model chiral axial rotation emerges naturally from the 3D flagellar dynamics. We perform high-speed imaging to measure key simulation parameters, which successfully reproduce the experimentally observed dynamics. Finally, we demonstrate how this coupling between signal detection and motor output constitutes a universal strategy for responding to an arbitrary, vectorial stimulus. |
Tuesday, March 3, 2020 9:12AM - 9:24AM |
F15.00005: Bacterial swarming: Motion under extreme forces? Irakli Gudavadze, Janelle Korf, Ernst-Ludwig Florin Bacterial swarming is a rapid, collective movement of bacteria over a surface powered by rotating flagella [1]. Unlike swimming, swarming takes place in thin liquid films, constraining bacteria to two dimensions. So far, it always has been assumed that the film is thicker than the diameter of a bacterium, but its exact thickness has never been measured. Here we present a novel method for measuring film thickness with tens of nanometer precision. For Bacillus subtilis colonies grown on agar gels, we find film thicknesses as thin or even thinner than the diameter of a single bacterium. For thicknesses thinner than a single bacterium, surface tension forces are expected to be on the order of tens of nanonewtons. These forces are about 4 orders of magnitudes greater than forces bacteria experience during swimming [2]. It remains unclear how flagella driven motility can be achieved under such strong confinement. |
Tuesday, March 3, 2020 9:24AM - 9:36AM |
F15.00006: Analysis of run-reverse-reorient motility of Helicobacter pylori and its ΔChePep mutant1 Wentian Liao, Maira A Constantino, Manuel Ricardo Amieva, Rama Bansil The gastric disease causing bacteria, Helicobacter pylori utilize flagella driven motility and chemotaxis to detect external signals as they swim away from acid to cross the mucus layer and colonize the epithelial surface of the stomach. The lack of the chemotaxis regulator protein ChePep leads to increased reversal frequency (Howitt et al2). We analyze translational and cell body rotational motility data obtained by phase contrast microscopy to compare the speed and turn angle distribution of the wild type (WT) with the ΔChePep mutant and compare with run-reversal-reorient model and Resistive Force Theory calculations of torque. We observe higher reversal frequency of ΔChePep in agreement with previous observation, however the cell body rotational rate and torque are not influenced by the lack of protein ChePep. Interestingly, both WT and ΔChePep are most likely to maintain their initial run speed after a reorientation or a reversal event, although the distribution of the change in speed indicates that large speed changes by factor of two and beyond are possible. |
Tuesday, March 3, 2020 9:36AM - 9:48AM |
F15.00007: Force and torque on a rotating helical flagellum near a boundary Bruce Rodenborn, Cesar Romero, Jin Lee, Hoa Nguyen, Orrin Shindell As a free swimming bacterium approaches a boundary, both the propulsive force and torque on its helical flagellum increase rapidly. Though a constrained helical swimmer pumps the fluid, a similar increase in force and torque occur near a boundary (Das et al. 2018). We use scaled macroscopic experiments to measure this functional dependence of the the force and torque as a constrained rotating helical flagellum approaches a boundary. We keep the Reynolds number in the experiments much less than unity to model bacterial fluid dynamics. These Reynolds-number-scaled experiments are compared with numerical simulations that use the method of images for regularized Stokeslets (Ainley et al. 2008). The computations find a similar functional dependence of force and torque on boundary distance. We also compare the results to biological measurements that use total internal reflection fluorescence microscopy to simultaneously measure the distance to the boundary and the dynamics of the bacteria. We show that all of the data can be collapsed onto a single curve by non-dimensionalizing the force, torque and boundary distance appropriately. |
Tuesday, March 3, 2020 9:48AM - 10:00AM |
F15.00008: A minimal neural reaction-diffusion model which generates C. elegans undulation Harold Hastings, Jenny Magnes, Kathleen Susman, Cheris C Congo, Miranda R Hulsey-Vincent, Anshul Singhvi, Rifah Tasnim, Naol Negassa The small (1 mm) nematode Caenorhabditis elegans has become widely used as a model organism; in particular the C. elegans connectome has been completely mapped and C. elegans locomotion has been widely studied (c.f. http://www.wormbook.org/). We describe a minimal reaction-diffusion model for the C. elegans central pattern generator (CPG) (c.f. Xu et al. 2018, Wen et al. 2012). We use simulation methods to show that a small network of FitzHugh (1961)-Nagumo (et al. 1962) neurons (one of the simplest neuronal models) can generate key features of C. elegans undulation (c.f. Magnes et al. 2017) and thus locomotion. Compare the neuromechanical model of Izquierdo and Beer (2015). We also investigate dynamics and stability of the model. |
Tuesday, March 3, 2020 10:00AM - 10:12AM |
F15.00009: Swimmers at low Reynolds number driven by Quincke rotation Endao Han, Lailai Zhu, Joshua Shaevitz, Howard A Stone In biological systems, the rotation and oscillation of flagella and cilia play important roles in realizing certain functions, such as self-propulsion and fluid mixing. Most previous attempts to build artificial small swimmers use an oscillatory drive. Here we present an artificial swimmer at low Reynolds number driven by an elasto-electro-hydrodynamic instability [1] based on Quincke rotation: a sphere in oil rotates in the presence of a high DC electric field. In our experiments, by attaching thin elastic fibers to a solid plastic sphere, we created swimmers that exhibit diverse behaviors when varying different control parameters. We demonstrate that the flexibility of the fibers leads to multiple stable states, where the swimmer can have unidirectional rotation or oscillatory motion controlled by the applied field. Furthermore, we relate these modes of motion to the kinematic properties of the swimmer such as the rotational speed and the ability to generate locomotion. |
Tuesday, March 3, 2020 10:12AM - 10:24AM |
F15.00010: Aerotaxis in Sinorhizobium meliloti, a soil bacterium Julien Bouvard, Frederic Moisy, Harold Auradou The legume family needs the help of soil bacteria to fix the atmospheric nitrogen they need to grow. In order to do so, such bacteria, called rhizobia, are swimming towards the plants by following the chemical gradient created by their roots. One of the most common member of the rhizobia family, Sinorhizobium meliloti, is displaying this chemotactic behaviour as well as an aerotactic one. To study and compare this not yet referenced aerotaxis to the already found chemotaxis, we made a few experimental set-ups. The first one consists of a sealed chamber containing S. meliloti, in which we insert an air bubble. The second one is a capillary filled with bacteria, sealed at one end and closed with PDMS at the other. In these experiments, we notice the formation of a profile of motile bacteria peaked at the interface with the air bubble or the PDMS. We also uses microfluidic devices to control the oxygen gradient in which the bacteria are swimming. The characterization of the swimming behaviour in presence of oxygen will help us understand the motility of S. meliloti in situ, and thus could lead us to some culture optimizations. |
Tuesday, March 3, 2020 10:24AM - 10:36AM |
F15.00011: Pairwise and Collective Interactions of a Model Swimmer at Intermediate Reynolds Numbers Thomas Dombrowski, Amneet Pal Singh Bhalla, Boyce E. Griffith, Daphne Klotsa In between the two extremes of Stokes flow, home to microorganisms, and inviscid flow, home to human swimmers and large fish, resides the less studied intermediate Reynolds regime where millimeter to centimeter sized organisms thrive. Here, both viscosity and inertia play a role in an organism’s movement, and few models have been developed which relate movement to general underlying physical mechanisms. In this presentation, we investigate pairwise interactions between reciprocal, asymmetric dumb-bell swimmers at intermediate Reynolds numbers (Re). Even for a single swimmer we find interesting behavior: a transition in the swimming direction from a small-sphere-leading to a large-sphere-leading regime. Their pairwise interactions are just as surprising. We computationally vary a broad range of parameters and find a wealth of states: steady pairs that cooperatively swim differently from individual swimmers under identical conditions, bi-stable pairs, orbits, and diverging paths. Averaged flow fields are analyzed to further understand these configurations. We continue by studying the collective behavior of large numbers of swimmers (up to a hundred) in order to identify pairwise versus many-body emergent behaviors. |
Tuesday, March 3, 2020 10:36AM - 10:48AM |
F15.00012: Hydrodynamics of biomimetic propulsion using externally and internally actuated fins Ersan Demirer, Alexander Alexeev We combine experiments and computer simulations to examine the hydrodynamics of two different actuation types that can be used to actuate an elastic plate to serve as a biomimetic propulsor in robotic fish. In the first case the elastic palate is actuated to perform sinusoidal plunging at the root, whereas in the second case the actuation is due to a distributed internal bending moment that represents piezoelectric actuation of smart materials such as macro fiber composites. The Morison equation is often used to characterize the forces acting on oscillating submerged bodies in terms of two parameters: the inertia and drag coefficients. We evaluate these parameters using our simulations and experiments. We find close agreement between the experiments and simulations for both actuation types. We find that the inertia coefficient depends strongly on the actuation type and the magnitude of the trailing edge displacement. We rationalize this dependency by analyzing the differences in the kinematics of the plates with different actuation types. Our results are useful for developing efficient propulsors for biomimetic underwater locomotion. |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700