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 D24: Biofluids: Biofilms I |
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Chair: Siddarth Srinivasan, Harvard University Room: 302 |
Sunday, November 22, 2015 2:10PM - 2:23PM |
D24.00001: Quasi-chemostat behavior in the leading edge of B. subtilis biofilms Siddarth Srinivasan, Lakshminarayanan Mahadevan, Shmuel Rubinstein \emph{Bacillus subtilis} is a gram positive bacterium that is a model system commonly used to study biofilm formation. By performing wide-field time-lapse microscopy on a fluorescently labeled \emph{B. subtilis} strain, we observe a well defined steady boundary layer at the edge of a biofilm growing on an nutrient infused agar gel substrate, within which the outward radial expansion growth predominantly occurs. Using distinct fluorescent protein markers as proxies of gene expression, we quantitatively measure how the width, velocity and ratio of motile cell to matrix cell phenotypes within this boundary layer responds to changes in environmental conditions (such as substrate agar percentage \& temperature). We further propose that the steady state at the leading edge can be interpreted as a quasi-chemostat which may enable well controlled response experiments on a colony scale. Finally, we show that for low agar concentration (0.5 wt\%), the cells exhibit swarming behavior, whose dynamics and swimming velocities are characterized using differential dynamic microscopy. We show the swarming state is associated with an unstable front which gives rise to fingering and branching growth patterns, illustrating the varied morphological response of the biofilm to environmental conditions [Preview Abstract] |
Sunday, November 22, 2015 2:23PM - 2:36PM |
D24.00002: Exploring the mechanisms of rising bubbles in marine biofouling prevention Mark Menesses, Jesse Belden, Natasha Dickenson, James Bird Fluid motion, such as flow past a ship, is known to inhibit the growth of marine biofouling. Bubbles rising along a submerged structure also exhibit this behavior, which is typically attributed to buoyancy induced flow. However, the bubble interface may also have a direct influence on inhibiting growth that is independent of the surrounding flow. Here we aim to decouple these two mechanisms through a combination of field and laboratory experiments. In this study, a wall jet and a stream of bubbles are used to create two flows near a submerged solid surface where biofouling occurs. The flow structure characteristics were recorded using PIV. This experimental analysis allows for us to compare the efficacy of each flow relative to its flow parameters. Exploration of the mechanisms at play in the prevention of biofouling by use of rising bubbles provides a foundation to predict and optimize this antifouling technique under various conditions. [Preview Abstract] |
Sunday, November 22, 2015 2:36PM - 2:49PM |
D24.00003: ABSTRACT WITHDRAWN |
Sunday, November 22, 2015 2:49PM - 3:02PM |
D24.00004: Biofilm formation over surface patterned with pico-liter oil micro-drop array Maryam Jalali, Jian Sheng It has been suggested that biodegradation by microbes is an effective process in the cleansing of oil polluted marine environments. It has also been speculated that dispersants could further enhance processes amid no direct evidence. The studies in the relevant scales are severely hampered by lack of techniques to generate uniform micro-scale drops allowing \textit{in-situ} monitoring of these processes. In this paper, we present a microfabrication technique allowing patterning microfluidic surfaces with arrays of micro oil drops. The array of oil drops was printed by micro transfer molding/printing with negative PDMS stamps. The printed micro-drops have dimensions ranging from 5 $\mu$m to 50 $\mu$m. Non-circular shapes, such as square and triangle, can also be printed and maintained for weeks. Atomic force microscopy is used to characterize the topology and interfacial structures of droplets. The results reveal that although the drop with different base shapes assumes dome like profile asymptotically, donut and top-hat shapes are also observed. Time evolution measurement elucidates that in the absences of inviscid mechanisms in comparison to a micro-liter drop, subtle interplays between interfacial forces and viscosity play crucial role in the shape of pico-liter drop. With the developed surfaces, the effects of oil drop sizes and interfacial structures on biofilm formation are studied and reported. [Preview Abstract] |
Sunday, November 22, 2015 3:02PM - 3:15PM |
D24.00005: Tear film dynamics: modeling the glycocalyx as a porous medium Javed Siddique, Antonio Mastroberardinob,, Richard Braun, Daniel Anderson The human tear film is a complex fluid structure composed of multiple layers: an aqueous layer that comprises most of the film and an outermost thinner lipid layer coat a forest of large transmembrane mucins at the epithelial surface. The glycocalyx helps provide stability to the ocular surface by assisting the tear film to wet it. It is also permeable to water, but less so to ions. We formulate a thin film model based on lubrication theory in order to understand the dynamics between the aqueous layer and the glycocalyx, which we treat as a rigid porous medium. We present numerical solutions for the evolution of the tear film and discuss the roles played by the key parameters of the system. [Preview Abstract] |
Sunday, November 22, 2015 3:15PM - 3:28PM |
D24.00006: Biomechanical ordering and buckling due to microbial growth confined at oil-water interfaces Gabriel Juarez, Roman Stocker Bacteria are unicellular organisms that often exist as densely populated, surface-associated communities. Bacteria are also environmental colloids and spontaneously attach and self-assemble at liquid-liquid interfaces. Here, we present results on the growth dynamics of individual rod-shaped bacteria confined to finite oil-water interfaces of varying curvature. Through experiments using microfluidic chambers and time-lapse microscopy, we study the formation of macroscopic structures observed as adsorbed bacteria grow, divide, and self-assemble in a nematic phase due to biomechanical interactions. The continued growth at the interface leads to a jammed monolayer of cells, which then causes the interface to buckle and undergo large deformations including wrinkling and tubulation. These observations highlight the interplay between physical environment, such as confinement and interface curvature, and active biological processes, such as growth, at the scale of individual agents and shape our understanding of macroscale processes such as microbial degradation of oil in the ocean. [Preview Abstract] |
Sunday, November 22, 2015 3:28PM - 3:41PM |
D24.00007: A non-destructive method for characterizing phenotypes and growth of a \textit{Bacillus subtilis} biofilm using fluorescence microscopy Stephan Koehler, Xiaoling Wang, James Wilking, Dave Weitz We develop an imaging technique for characterizing growth of biofilms using a triple fluorescent labeled strain for the three main phenotypes of a Bacillus subtilis biofilm on an agar substrate. We find that the biofilm does not flow across the substrate and thus growth is due to colonization at the periphery and thickening of the interior regions. We obtain local height and its composition of the three main phenotypes, which are motile, matrix-producing and sporulating, as well as the non-fluorescent material, which can be spores, dormant or dead cells or extracellular matrix. This technique is suitable for the study of biofilm growth and inhibition for different conditions such as biocides or bioremediation. [Preview Abstract] |
Sunday, November 22, 2015 3:41PM - 3:54PM |
D24.00008: PIV measurements of hydrodynamic interactions between biofilms and flow Kenneth T. Christensen, Farzan Kazemifar, Marcelo Aybar, Patricia Perez-Calleja, Robert Nerenberg, Sumit Sinha, Richard J. Hardy, Jim L. Best, Greg H. Sambrook Smith Biofilms constitute an important form of bacterial life in aquatic environments and are present at the interface of fluids and solid such as riverbeds or bridge columns. They are also utilized in bioreactors for bioremediation and water treatment purposes. They are permeable, heterogeneous, and deformable structures that can influence the flow and mass/momentum transport, yet their interaction with flow is not fully understood in part due to technical obstacles impeding quantitative experimental investigations. We have attempted to address these challenges using the PIV technique and fluorescence imaging to investigate the flow field around cylinders covered with biofilms at different growth stages. These measurements are meant to uncover the coupled dynamics of turbulence and the biofilm development. Preliminary results of PIV measurements of flow-biofilm interactions in channel flow will be presented. [Preview Abstract] |
Sunday, November 22, 2015 3:54PM - 4:07PM |
D24.00009: Modeling Tear Film Evaporation and Breakup with Duplex Films Michael Stapf, Richard Braun, Carolyn Begley, Tobin Driscoll, Peter Ewen King-Smith Tear film thinning, hyperosmolarity, and breakup can irritate and damage the ocular surface. Recent research hypothesizes deficiencies in the lipid layer may cause locally increased evaporation, inducing conditions for breakup. We consider a model for team film evolution incorporating two mobile fluid layers, the aqueous and lipid layers. In addition, we include the effects of salt concentration, osmosis, evaporation as modified by the lipid layer, and the polar portion of the lipid layer. Numerically solving the resulting model, we explore the conditions for tear film breakup and analyze the response of the system to changes in our parameters. Our studies indicate sufficiently fast peak values or sufficiently wide areas of evaporation promote TBU, as does diffusion of solutes. In addition, the Marangoni effect representing polar lipids dominates viscous dissipation from the non-polar lipid layer in the model. [Preview Abstract] |
Sunday, November 22, 2015 4:07PM - 4:20PM |
D24.00010: We need wrinkle on the skin Sungsook Ahn, Sang Joon Lee Wrinkle formation on the skin is an unwelcome guest to everybody. But if we truly understand how wrinkles can contribute to important biological functions, then we readily admit the wrinkles positively. In this study, we show how the wrinkles are advantageous and useful in many systems. In a plant system for example, by forming line patterned wrinkles the hydrogels covering on the seed surface contribute to delay the dehydration against varying water supply environments. Inspired by this plant hydrogel, it is experimentally and theoretically investigated how lined wrinkles are useful to conserve water inside while protect the individual from drying-out. This study would contribute to a variety of humidity-sensitive system development including artificial skin, humidity-actuated sensors and the like. [Preview Abstract] |
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