Bulletin of the American Physical Society
66th Annual Meeting of the APS Division of Fluid Dynamics
Volume 58, Number 18
Sunday–Tuesday, November 24–26, 2013; Pittsburgh, Pennsylvania
Session M18: Biofluids: General VII - Biofilms |
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Chair: Knut Drescher, Princeton University Room: 306/307 |
Tuesday, November 26, 2013 8:00AM - 8:13AM |
M18.00001: A framework to understand cell type transitions in bacterial biofilms Agnese Seminara, Naveen Sinha, James Wilking, Stephane Koelher, Matthew Cabeen, David Weitz, Michael Brenner Bacterial biofilms are colonies of cells that live associated to surfaces and differentiate into different cell types, in response to unknown environmental cues. Similar to the development of multicellular organisms, differentiation happens in reproducible spatio-temporal patterns of gene expression. Why do we see the patterns that we see? Fluorescence microscopy shows that there is a cell lineage specific to biofilms: cells are first motile, they then become matrix producers, and finally they sporulate. We combine this knowledge to the complete space-time distribution of fluorescence to study when and where the transitions among these three cell types arise. We first isolate the effect of growth and expansion on the evolution of the expression profiles to detect the cell type transitions. Based on these data we then elaborate a consistent scenario to explain cell type transitions. [Preview Abstract] |
Tuesday, November 26, 2013 8:13AM - 8:26AM |
M18.00002: Measurement of fluid dynamic loading on staphylococci bacteria bio-film structures using $\mu$PIV Erica Sherman, Derek Moormeier, Kenneth Bayles, John Davidson, Sangjin Ryu, Timothy Wei Staphylococci bacteria are recognized as the most frequent cause of biofilm-associated infections. Although humans are regularly exposed to these bacteria without consequence, a localized infection can enter the bloodstream and lead to serious infections such as endocarditis, pneumonia, or toxic shock syndrome. The mechanics of staphylococci biofilm formation and dispersion through the bloodstream are not well known. It has recently been observed that under certain flow conditions, bacteria organize in tower-like structures which break and are transported downstream by the flow. The fundamental questions of interest are i) whether or not fluid mechanics plays a role in differentiating between film or tower formation and ii) whether or not the faulty towers are a bio-film propagation mechanism. This talk focuses on the application of $\mu$PIV to study this problem. Staphylococcus aureus bacteria were cultured in the Bioflux Fluxion square microchannel of a 65 by 65 um cross section, and subjected to a steady shear rate of 0.5 dynes. $\mu$PIV measurements were made to map the flow over and around a biofilm tower structure which occluded approximately 66{\%} of the channel width. Data were recorded around the structure at a series of two dimensional planes, which when stacked vertically show a two dimensional flow field as a function of tower height. Measurements and control volume analysis will be presented quantifying forces acting on these structures. [Preview Abstract] |
Tuesday, November 26, 2013 8:26AM - 8:39AM |
M18.00003: Kinetic theory for actively streaming microtubule suspensions Tong Gao, Robert Blackwell, Matt Glaser, Meredith Betterton, Michael Shelley Suspensions of polar biopolymers mixed with molecular motor proteins can exhibit surprising out-of-equilibrium phenomena. In a recent experiment by Sanchez et al., microtubules are driven into collective motion by plus-end walking motor complexes. In experiments where the suspension is confined to a fluid-fluid interface, they find the emergence of distinctive large-scale flows characterized by persistent time-dependence and formation/annihilation of disclination singularities in the nematic order. Here we develop a first-principles kinetic theory to investigate the nonlinear dynamics and pattern formation observed in active microtubule suspensions. We model the active stresses generated by motile microtubules by taking into account the extensile stresses due to both the antiparallel and the parallel microtubule pairs. In a concentrated system, the resultant particle-pair stresses can induce hydrodynamic instabilities, and lead to a large-scale flows. When the suspension is confined to a liquid-liquid interface, we recover much of the dynamics observed in the experiments. [Preview Abstract] |
Tuesday, November 26, 2013 8:39AM - 8:52AM |
M18.00004: Mathematical Modeling of Tear Film Break up Modes and Fluorescent Intensity Javed Siddique, Richard Braun, Carolyn Begley, Adam Winkeler, Peter E. King-Smith The purpose of this study is to develop mathematical model for variables of interest in tear film break up (TBU) to compare with experimental images of TBU to better predict local values of tear film osmolarity and fluorescence during and following the TBU. Models are developed for local changes tear film thickness, insoluble surfactant concentration as well as osmolarity and fluorescein concentration inside the tear film. Fluorescence concentration was converted to fluorescent intensity using the expression involving film thickness and the full range of fluorescence as described by Nichols et al (IOVS 2012). The fluorescent intensity response is a primary tool for visualizing the tear film thickness, and it is qualitatively different in the dilute vs concentrated regimes. Computed results over a wide range of fluorescein concentrations show that elevated surfactant concentration or evaporation rate led to thinner regions where TBU first occurs. The model predicts locally elevated concentration of osmolarity within areas of TBU and fluorescence intensity patterns very similar to computed thickness and the observed experimental results. The osmolarity may increase from 50$\%$ to 1300$\%$ of the isosmolar value, depending sensitively on the corneal permeability. [Preview Abstract] |
Tuesday, November 26, 2013 8:52AM - 9:05AM |
M18.00005: Physical solutions to the public goods dilemma in bacterial biofilms Knut Drescher, Carey Nadell, Howard Stone, Ned Wingreen, Bonnie Bassler Bacteria frequently live in densely populated surface-bound communities, termed biofilms. Biofilm-dwelling cells rely on secretion of extracellular substances to construct their communities and to capture nutrients from the environment. Some secreted factors behave as cooperative public goods: they can be exploited by non-producing cells. The means by which public good producing bacteria avert exploitation in biofilm environments are largely unknown. Using experiments with \textit{Vibrio cholerae}, which secretes extracellular enzymes to digest its primary food source, the solid polymer chitin, we show that the public goods dilemma may be solved by two dramatically different, physical mechanisms: cells can produce thick biofilms that confine the goods to producers, or fluid flow can remove soluble products of chitin digestion, denying access to non-producers. Both processes limit the distance over which enzyme-secreting cells provide a benefit to neighbors, resulting in preferential benefit to nearby clonemates. Our results demonstrate how bacterial physiology and environmental conditions can interact with social phenotypes to influence the evolutionary dynamics of cooperation within biofilms. [Preview Abstract] |
Tuesday, November 26, 2013 9:05AM - 9:18AM |
M18.00006: Coupling Osmolarity Dynamics within Human Tear Film on an Eye-Shaped Domain Longfei Li, R.J. Braun, T.A. Driscoll, W.D. Henshaw, J.W. Banks, P.E. King-Smith The concentration of ions in the tear film (osmolarity) is a key variable in understanding dry eye symptoms and disease. We derived a mathematical model that couples osmolarity (treated as a single solute) and fluid dynamics within the tear film on a 2D eye-shaped domain. The model concerns the physical effects of evaporation, surface tension, viscosity, ocular surface wettability, osmolarity, osmosis 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 new hybrid time stepping scheme (using variable step BDF and RKC) that was added to the framework. Results of our numerical simulations show good agreement with existing 1D models (for both tear film and osmolarity dynamics) and provide new insight about the osmolarity distribution over the ocular surface during the interblink. [Preview Abstract] |
Tuesday, November 26, 2013 9:18AM - 9:31AM |
M18.00007: Thin film drainage between pre-inflated capsules or vesicles Martin Keh, Johann Walter, Gary Leal Capsules and vesicles are often used as vehicles to carry active ingredients or fragrance in drug delivery and consumer products and oftentimes in these applications the particles may be pre-inflated due to the existence of a small osmotic pressure difference between the interior and exterior fluid. We study the dynamics of thin film drainage between capsules and vesicles in flow as it is crucial to fusion and deposition of the particles and, therefore, the stability and effectiveness of the products. Simulations are conducted using a numerical model coupling the boundary integral method for the motion of the fluids and a finite element method for the membrane mechanics. For low capillary numbers, the drainage behavior of vesicles and capsules are approximately the same, and also similar to that of drops as the flow-independent and uniform tension due to pre-inflation dominates. The tension due to deformation caused by flow will become more important as the strength of the external flow (i.e. the capillary number) increases. In this case, the shapes of the thin film region are fundamentally different for capsules and vesicles, and the drainage behavior in both cases differs from a drop. [Preview Abstract] |
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