Bulletin of the American Physical Society
65th Annual Meeting of the APS Division of Fluid Dynamics
Volume 57, Number 17
Sunday–Tuesday, November 18–20, 2012; San Diego, California
Session R16: Biofluids: Biofilms and Membranes |
Hide Abstracts |
Chair: Howard Stone, Princeton University Room: 28B |
Tuesday, November 20, 2012 1:00PM - 1:13PM |
R16.00001: Biofilm streamers cause rapid clogging of flow systems Yi Shen, Knut Drescher, Ned Wingreen, Bonnie Bassler, Howard Stone Biofilms are antibiotic-resistant, sessile bacterial communities that are found on most surfaces on Earth. In addition to constituting the most abundant form of bacterial life, biofilms also cause chronic and medical device-associated infections. Despite their importance, basic information about how biofilms behave in common ecological environments is lacking. Here we demonstrate that flow through soil-like porous materials, industrial filters, and medical stents dramatically modifies the morphology of \textit{Pseudomonas aeruginosa} biofilms to form streamers which over time bridge the space between obstacles and corners in non-uniform environments. Using a microfluidic model system we find that, contrary to the accepted paradigm, the accumulation of surface-attached bacterial biofilm has little effect on flow resistance whereas the formation of biofilm streamers causes sudden and rapid clogging. The time at which clogging happens depends on bacterial growth, while the duration of the clogging transition is driven by flow-mediated transport of bacteria to the clogging site. Flow-induced shedding of extracellular matrix from the resident biofilm generates a sieve-like network that catches bacteria flowing by, which add to the network of extracellular matrix, to cause exponentially rapid clogging. We expect these biofilm streamers to be ubiquitous in nature, and to have profound effects on flow through porous materials in environmental, industrial, and medical environments. [Preview Abstract] |
Tuesday, November 20, 2012 1:13PM - 1:26PM |
R16.00002: The ``Swiss cheese'' instability of bacterial biofilms Hongchul Jang, Roberto Rusconi, Roman Stocker Bacteria often adhere to surfaces, where they develop polymer-encased communities (biofilms) that display dramatic resistance to antibiotic treatment. A better understanding of cell detachment from biofilms may lead to novel strategies for biofilm disruption. Here we describe a new detachment mode, whereby a biofilm develops a nearly regular array of $\sim $50-100 $\mu $m holes. Using surface-treated microfluidic devices, we create biofilms of controlled shape and size. After the passage of an air plug, the break-up of the residual thin liquid film scrapes and rearranges bacteria on the surface, such that a ``Swiss cheese'' pattern is left in the residual biofilm. Fluorescent staining of the polymeric matrix (EPS) reveals that resistance to cell dislodgement correlates with local biofilm age, early settlers having had more time to hunker down. Because few survivors suffice to regrow a biofilm, these results point at the importance of considering microscale heterogeneity in assessing the effectiveness of biofilm removal strategies. [Preview Abstract] |
Tuesday, November 20, 2012 1:26PM - 1:39PM |
R16.00003: (How) do biofilms control their morphology? Agnese Seminara, Naveen Sinha, James Wilking, David Weitz, Michael Brenner Bacterial biofilms are organized communities of cells living in association with surfaces. The hallmark of biofilm formation is a well defined spatio-temporal pattern of gene expression, leading to differentiation and a complex morphology. While this process resembles the development of a multicellular organism, biofilms are only transiently multicellular. More importantly the functions associated to the biofilm phenotype are largely unknown. Here we discuss aspects of biofilm physiology connected to motility and nutrient uptake. We develop a connection between patterns of gene expression and morphology and finally we propose a framework to understand how these gene expression patterns may be generated and possibly controlled. [Preview Abstract] |
Tuesday, November 20, 2012 1:39PM - 1:52PM |
R16.00004: Morphological Approach toward Elucidating Transport and Shear Behavior of Biofilms Aloke Kumar, Pallab Barai, Partha Mukherjee Biofilms are complex three-dimensional matrix encapsulated aggregations of microbes that grow on a solid surface. Distribution of microbes inside the matrix or extracellular polymer substances (EPS) affects diffusive transport as well as mechanical response of the biofilm under shear induced deformation. In this work, a morphology-aware computational approach encompassing a digital representation of the biofilm is presented. Confocal microscopy images of biofilms are employed for the digital morphology constructs. For mechanical response under shear, the biofilm can be viewed as rigid bacteria inclusions dispersed inside a cross-linked polymer gel (EPS). The digital biofilm model takes into account the unfolding behavior of proteins to characterize the mechanical response of the EPS. Experimentally observed strain stiffening behavior of biofilms has been captured using the computational approach. Transport simulation reveals the influence of bacterial loading and aggregates in the biofilm on the diffusion behavior. [Preview Abstract] |
Tuesday, November 20, 2012 1:52PM - 2:05PM |
R16.00005: Reflection and refraction of flexural waves in membranes with complex geometry Arthur Evans, Basanta Bhaduri, Ryan Tapping, Gabriel Popescu, Alex Levine Undulatory waves on membranes are studied in a variety of contexts including microrheology of red blood cell membranes, giant vesicles, and various cellular mimics, such as actin coated vesicles. While the fundamental understanding of undulatory dynamics in flat membranes is well known, the problem is significantly more interesting for waves on curved membranes, where geometry couples bending and stretching in the surface. In this talk we report on analysis of flexural wave dynamics in curved membranes and draw a useful analogy between the propagation of these waves and physical optics. We obtain an analog of Snell's law for the reflection and refraction of undulatory waves at interfaces at which the local mean and Gaussian curvature of the surface changes abruptly. In addition, we show that, due to the higher order derivatives in the force balance equation, bending waves on curved membranes generically exhibit characteristics associated with waves in classical optics, such as birefringence and total internal reflection. Using this latter insight, we analyze the experimentally observed spatial distribution of the amplitude of red blood cell membrane undulations, and show that one can understand their spatial structure in terms of the local geometry of the cell. [Preview Abstract] |
Tuesday, November 20, 2012 2:05PM - 2:18PM |
R16.00006: Deformation and stability of biomimetic membranes in DC electric pulses Paul Salipante, Petia Vlahovska Electrohydrodynamics of vesicles (closed bilayer membranes) made of lipids or polymers are investigated both experimentally and theoretically. When a uniform electric field is applied across a membrane, free charges accumulate on both sides of the membrane and the membrane acts as a capacitor. While the membrane is charging, the vesicle deforms into either an oblate or prolate ellipsoid depending on the bulk fluids conductivities. However, once the membrane is fully charged the vesicle adopts a prolate shape. The evolution of vesicle shape, and in particular the oblate-prolate transition, is experimentally studied for DC pulses of different strength and durations. Membrane composition is varied to observe the effect of membrane viscosity, bending rigidity, and membrane capacitance. The results show that the transient response of the vesicle is sensitive to membrane viscosity, while the steady state shape is mainly controlled by membrane tension. Strong DC pulses, typically used in cell electroporation, induce an instability in both lipid and polymer membranes. The instability leads to vesicle collapse, where the timescale of collapse shows a $t\sim1/E^2$ dependence. [Preview Abstract] |
Tuesday, November 20, 2012 2:18PM - 2:31PM |
R16.00007: Influence of membrane viscosity on dynamics of capsules and red blood cells Alireza Yazdani, Prosenjit Bagchi Most previous continuum-level numerical studies on capsule and erythrocyte dynamics have ignored the role of membrane viscosity. We present a numerical method using a Kelvin--Voigt viscoelastic model for the capsule membrane. We observe that the membrane viscosity leads to buckling in the range of shear rate in which no buckling is observed for capsules with purely elastic membrane. For moderate to large shear rates, the wrinkles on the capsule surface appear in the same range of the membrane viscosity that was reported earlier for artificial capsules and red blood cells based on experimental measurements. It is also observed that the bending stiffness required to obtain stable shapes is also in the same range as that reported for the red blood cells, but considerably higher than that estimated for artificial capsules. Membrane viscosity is observed to reduce cell deformation, and introduce a damped oscillation in time-dependent deformation and inclination. The time-averaged inclination angle and the tank-treading frequency show nonmonotonic trends with increasing membrane viscosity. Further, the dynamics of a non-spherical capsule is observed to change from a swinging motion to a tumbling motion with increasing membrane viscosity. [Preview Abstract] |
Tuesday, November 20, 2012 2:31PM - 2:44PM |
R16.00008: Pair-collision between heterogeneous capsules in simple shear: Effect of membrane stiffness and membrane constitutive laws Rajesh Singh, Kausik Sarkar Deformability of red blood cells affects hydrodynamic properties of blood and thereby physiological functions in many cardiovascular diseases, e.g. in sickle cell anemia and malaria, the cell membrane becomes stiff affecting their circulation through microvessels. Here, we numerically simulate the hydrodynamic interaction between a pair of cell-like capsules in a free shear flow, using a front-tracking method. The membrane is modeled using various constitutive equations. By varying the stiffness of one capsule (C$_{2})$ and keeping all other parameters constant, we find a significant effect on the deformation and trajectory of the other (C$_{1})$. Increasing the stiffness of C$_{2}$ surprisingly increases the peak deformation of C$_{1}$ while decreasing the cross-stream shift in its trajectory However, the relative trajectory between capsules remains the same. Effects of constitutive laws and difference in behaviors between capsules and drops are investigated explaining underlying physics. [Preview Abstract] |
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