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 G24: Biofluids: Biofilms II |
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Chair: Justas Dauparas, University of Cambridge Room: 302 |
Monday, November 23, 2015 8:00AM - 8:13AM |
G24.00001: Flows around bacterial swarms Justas Dauparas, Eric Lauga Flagellated bacteria on nutrient-rich substrates can differentiate into a swarming state and move in dense swarms across surfaces. A recent experiment (HC Berg, Harvard University) measured the flow in the fluid around the swarm. A systematic chiral flow was observed in the clockwise direction (when viewed from above) ahead of a E.coli swarm with flow speeds of about 10$\mu$m/s, about 3 times greater than the radial velocity at the edge of the swarm. The working hypothesis is that this flow is due to the flagella of cells stalled at the edge of a colony which extend their flagellar filaments outwards, moving fluid over the virgin agar. In this talk we quantitatively test his hypothesis. We first build an analytical model of the flow induced by a single flagellum in a thin film and then use the model, and its extension to multiple flagella, to compare with experimental measurements. [Preview Abstract] |
Monday, November 23, 2015 8:13AM - 8:26AM |
G24.00002: Bacterial floc mediated rapid streamer formation in creeping flows Mahtab Hassanpourfard, Zahra Nikakhtari, Ranajay Ghosh, Siddhartha Das, Thomas Thundat, Aloke Kumar One of the contentious problems regarding the interaction of low Reynolds number (Re\textless \textless 1) fluid flow with bacterial biomass is the formation of filamentous structures called streamers. Recently, we discovered that streamers can be formed from flow-induced deformation of the pre-formed bacterial flocs over extremely small timescales (less than a second). However, these streamers are different than the ones that mediated by biofilms. To optically probe the inception process of these streamers formation, bacterial flocs were embedded with 200 nm red fluorescent polystyrene beads that served as tracers. We also showed that at their inception the deformation of the flocs is dominated by large recoverable strains indicating significant elasticity. These strains subsequently increase tremendously to produce filamentous streamers. At time scales larger than streamers formation time scale, viscous response was observed from streamers. Finally, rapid clogging of microfluidic devices occurred after these streamers formed. [Preview Abstract] |
Monday, November 23, 2015 8:26AM - 8:39AM |
G24.00003: Exploration of fluid dynamic indicators/causative factors in the formation of tower structures in staphylococci bacteria bio-films Erica Sherman, Moormeier Derek, Kenneth Bayles, Timothy Wei \textit{Staphylococcus aureus} bacteria form biofilms with distinct structures that facilitate their ability to tolerate treatment and to spread within the body. As such, staph infections represent one of the greatest threats to post-surgery patients. It has been found that flow conditions play a significant role in the developmental and dispersal activity of a biofilm. The coupling between the growing biofilm and surrounding flow, however, is not well understood. Indeed, little is know why bacteria form tower structures under certain conditions but not in a predictable way. $\mu$-PTV measurements were made in a microchannel to try to identify fluid dynamic indicators for the formation of towers in biofilm growth. Preliminary experiments indicated changes in the near wall flow up to five hours before a tower formed. The reason for that is the target of this investigation. \textit{Staphylococcus aureus} bacteria were cultured in the Bioflux Fluxion channel and subjected to a steady shear rate of 0.5 dynes. In addition to $\mu$-PTV measurement, nuclease production and cell number density counts were observed prior to and during tower development. These were compared against measurements made under the same nominal flow conditions where a tower did not form. [Preview Abstract] |
Monday, November 23, 2015 8:39AM - 8:52AM |
G24.00004: A Model Problem for Blob-Driven Tear Film Breakup (TBU) Lan Zhong, C.F. Ketelaar, R.J. Braun, T.A. Driscoll, P.E. King-Smith, Carolyn G. Begley A model problem is developed to simulate tear film break up by assuming the existence of a flexible non-spreading blob with constant surfactant surface concentration. These assumptions model in vivo observations of an excess of tear film lipid that does not spread, with the surfactant concentration approximating the lipid layer. The model includes the effects of evaporation, osmolarity, surface tension, viscosity, the Marangoni effect and insoluble surfactant transport. The evaporative fluxes are input as representative functions based on data from experiments. A strong flow driven by surface tension gradient is observed from the numerical results, which may drive TBU at times compatible with in vivo observations. The TBU dynamics are studied as functions of blob size, surfactant properties and other parameters to establish regimes were TBU may be driven primarily by Marangoni effects. [Preview Abstract] |
Monday, November 23, 2015 8:52AM - 9:05AM |
G24.00005: Bulk flow coupled to a viscous interfacial film sheared by a rotating knife edge Aditya Raghunandan, Fayaz Rasheed, Amir Hirsa, Juan Lopez The measurement of the interfacial properties of highly viscous biofilms, such as DPPC (the primary component of lung surfactant), present on the surface of liquids (bulk phase) continues to attract significant attention. Most measurement techniques rely on shearing the interfacial film and quantifying its viscous response in terms of a surface (excess) viscosity at the air-liquid interface. The knife edge viscometer offers a significant advantage over other approaches used to study highly viscous films as the film is directly sheared by a rotating knife edge in direct contact with the film. However, accurately quantifying the viscous response is non-trivial and involves accounting for the coupled interfacial and bulk phase flows. Here, we examine the nature of the viscous response of water insoluble DPPC films sheared in a knife edge viscometer over a range of surface packing, and its influence on the strength of the coupled bulk flow. Experimental results, obtained via Particle Image Velocimetry in the bulk and at the surface (via Brewster Angle Microscopy), are compared with numerical flow predictions to quantify the coupling across hydrodynamic flow regimes, from the Stokes flow limit to regimes where flow inertia is significant. [Preview Abstract] |
Monday, November 23, 2015 9:05AM - 9:18AM |
G24.00006: Fibrillization kinetics of insulin solution in an interfacial shearing flow Vignesh Balaraj, Samantha McBride, Amir Hirsa, Juan Lopez Although the association of fibril plaques with neurodegenerative diseases like Alzheimer's and Parkinson's is well established, in-depth understanding of the roles played by various physical factors in seeding and growth of fibrils is far from well known. Of the numerous factors affecting this complex phenomenon, the effect of fluid flow and shear at interfaces is paramount as it is ubiquitous and the most varying factor in vivo. Many amyloidogenic proteins have been found to denature upon contact at hydrophobic interfaces due to the self-assembling nature of protein in its monomeric state. Here, fibrillization kinetics of insulin solution is studied in an interfacial shearing flow. The transient surface rheological response of the insulin solution to the flow and its effect on the bulk fibrillization process has been quantified. Minute differences in hydrophobic characteristics between two variants of insulin- Human recombinant and Bovine insulin are found to result in very different responses. Results presented will be in the form of fibrillization assays, images of fibril plaques formed, and changes in surface rheological properties of the insulin solution. The interfacial velocity field, measured from images (via Brewster Angle Microscopy), is compared with computations. [Preview Abstract] |
Monday, November 23, 2015 9:18AM - 9:31AM |
G24.00007: Interaction of bacterial wall with electrically charged solid substrate Vladimir Ajaev Recent experimental studies indicate that the electrically charged substrates can exhibit antibacterial properties above a certain threshold value of the charge density. To explain these observations, we develop a mathematical model of interaction between a bacterial wall, described as a charge-regulating surface, and a charged solid substrate. Viscous flow in the aqueous film separating the two surfaces is described by a lubrication-type equation. Electrical charge transport is incorporated into the model and coupled to the flow. The complex interplay between charge transport, electrostatic interaction of the surfaces, and viscous flow leads to criteria for the critical charge density needed to achieve antibacterial properties for a range of different types of harmful bacteria. [Preview Abstract] |
Monday, November 23, 2015 9:31AM - 9:44AM |
G24.00008: Solute Dynamics and Imaging in the Tear Film on an Eye-shaped Domain R.J. Braun, Longfei Li, William Henshaw, Tobin Driscoll, P.E. King-Smith The concentration of ions in the tear film (osmolarity) is a key variable in understanding dry eye symptoms and disease, yet its global distribution is not available; direct measurements are restricted to a region near the temporal canthus. It has been suggested that imaging methods that use solutes such as fluorescein can be used as a proxy for estimating the osmolarity. The concentration of fluorescein is not measured directly either but the intensity as a function of concentration and thickness of the film is well established. We derived a mathematical model that couples multiple solutes and fluid dynamics within the tear film on a 2D eye-shaped domain. The model includes the physical effects of evaporation, surface tension, viscosity, ocular surface wettability, osmolarity, osmosis, fluorescence and tear fluid supply and drainage. We solved the governing system of coupled nonlinear PDEs using the Overture computational framework developed at LLNL, together with a hybrid time stepping scheme (using variable step BDF and RKC). Results of our numerical simulations provide new insight about the osmolarity distribution and its connection with images obtained in vivo over the whole ocular surface and in local regions of tear thinning due to evaporation and other effects. [Preview Abstract] |
Monday, November 23, 2015 9:44AM - 9:57AM |
G24.00009: Characteristics of turbulent boundary layer flow over algal biofilm Elizabeth Murphy, Julio Barros, Michael Schultz, Cecily Steppe, Karen Flack, Matthew Reidenbach Algal biofilms are an important fouling community on ship hulls, with severe economic consequences due to drag-induced increases in fuel use and cleaning costs. Here, we characterize the boundary layer flow structure in turbulent flow over diatomaceous slime, a type of biofilm. Diatomaceous slime composed of three species of diatoms commonly found on ship hulls was grown on acrylic test plates under shear stress. The slime averages 1.6 mm in thickness and has a high density of streamers, which are flexible elongated growths with a length on the order of 1- 2 mm located at the top of the biofilm that interact with the flow. Fouled acrylic plates were placed in a water tunnel facility specialized for detailed turbulent boundary layer measurements. High resolution Particle Image Velocimetry (PIV) data are analyzed for mean velocity profile as well as local turbulent stresses and turbulent kinetic energy (TKE) production, dissipation and transport. Quadrant analysis is used to characterize the impact of the instantaneous events of Reynolds shear stress (RSS) in the flow. To investigate the coherence of the large-scale motion in the flow two-point correlation analysis is employed. [Preview Abstract] |
Monday, November 23, 2015 9:57AM - 10:10AM |
G24.00010: Impact of Diatomaceous Biofilms on the Frictional Drag of Ship Hull Coatings Michael Schultz, Jessica Walker, Cecily Steppe, Karen Flack Skin-friction results are presented for three commercial ship hull coatings in the unexposed, clean condition and after dynamic exposure to diatomaceous biofilms for 3 and 6 months. The experiments were conducted in a fully-developed turbulent channel flow facility spanning a wide Reynolds number range. Results show that the clean coatings tested are hydraulically-smooth over much of the Reynolds number range. Biofilms, however, result in an increase in skin-friction of up to 70\%. The roughness functions for the biofilm-covered surfaces do not display universal behavior. The effect of the biofilm is observed to scale with its mean thickness and the square root of the percent coverage. Boundary layer similarity-law scaling is used to predict the impact of these biofilms on the required shaft power for a mid-sized naval surface combatant at cruising speed. The increase in power is estimated to be between 1.5\% and 10.1\% depending on the biofilm thickness and percent coverage. [Preview Abstract] |
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