Bulletin of the American Physical Society
2005 58th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 20–22, 2005; Chicago, IL
Session LB: Bio-Fluid Dynamics: Creep, Crawl, Slither, Slide |
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Chair: Anette Hosoi, Massachusetts Institute of Technology Room: Hilton Chicago Waldorf |
Tuesday, November 22, 2005 8:00AM - 8:13AM |
LB.00001: Hydrodynamics of actin-based propulsion Alexander Leshansky Actin polymerization is a key element in the motility of many cells and bacteria. The motility of bacterium Listeria monocytogenes, self-propelled inside cells by growing of a soft elastic comet made of a filamentous actin network, considered as a model system for understanding motile functions involving actin polymerization. While biochemical aspects of comet growth are now well understood, the underlying physical mechanism of motion is still under debate. Recently proposed biomimetic systems have provided a significant advance in the understanding of the actin-based propulsion. In these experiments, the bacteria are replaced by microparticles (solid beads, vesicles or drops) covered with actin polymerization promoters. The microparticles submerged into cell extracts closely mimic the natural phenomena of actin comet formation and self-locomotion. A direct measurement of the forces generated during actin-based propulsion in micromanipulation experiments suggests that hydrodynamic forces may not play an important role in motility. On the other hand, for microparticles with actin tails that are not anchored, the hydrodynamics, in fact, controls the speed of the microparticle displacement. I develop a simple hydrodynamic theory of the actin-based propulsion. The working hypothesis is that the growing filaments act as a force dipole, whereas the propulsive force is determined by the balance of dissociated and attached filaments. We show that the theory agrees well with resent experimental observations concerning propulsion speed of microparticles of different shapes. [Preview Abstract] |
Tuesday, November 22, 2005 8:13AM - 8:26AM |
LB.00002: Controlling the motion of vesicles along compliant substrates Rolf Verberg, Alexander Alexeev, Anna Balazs To perform various biological assays and tissue engineering studies, it is vital to control the dynamic behavior of in vitro cells. In particular, there is a need for ``smart'' surfaces that can effectively modulate the motion of cells and thereby allow them to be readily sorted, isolated or encapsulated. To design such smart surfaces, one needs models that capture not only the fluid-membrane interactions, but also cell-substrate interactions. We present an approach that couples mesoscale models for hydrodynamics (lattice-Boltzmann) and micromechanics (lattice spring) to examine the dynamic interactions among an encapsulated fluid, the bounding elastic shell (membrane) and a compliant surface. By focusing on compliant surfaces, we find that simple modifications permit significant control over the motion of cells. In particular, we isolate systems that affect not only the cell's velocity, but also its way of moving along the surface. In addition, we uncover surface patterns that can drive the cells to stop at specified locations. Our findings yield guidelines for controlling in vitro trafficking of cells on elastic surfaces. [Preview Abstract] |
Tuesday, November 22, 2005 8:26AM - 8:39AM |
LB.00003: Shape Optimization of Swimming Sheets Jon Wilkening, Anette Hosoi The swimming behavior of a sheet which moves via wave propagation was first studied by G. I. Taylor in 1951. In addition to being of theoretical interest, this problem serves as a useful model of the locomotion of various micro-organisms and a few larger animals such as snails. We show how the shape of the wave affects the swimming speed and power required to swim, and present numerical techniques to find these optimal shapes when arclength and fluid volume are constrained. In the (small amplitude) lubrication approximation, we solve the Euler-Lagrange equations using a quadratically convergent Levenberg-Marquardt method for varying the parameters of the ODE until the constraints are satisfied. For the full Stokes equations, we represent the wave profile using periodic cubic splines and use finite elements to solve an adjoint problem to compute the variation of the power and speed with respect to changes in wave shape; we then use a limited memory BFGS method to find the optimal shape. Finally, we validate the lubrication theory by comparing with finite element calculations for the full Stokes equations. [Preview Abstract] |
Tuesday, November 22, 2005 8:39AM - 8:52AM |
LB.00004: Apple Snail: a Bio Cleaner of the Water Free Surface. Golnaz Bassiri, Nick Phelps, Khaled Sallam Oil spills from tankers represent a threat for shorelines and marine life. Despite continuing research, there has been little change in the fundamental technology for dealing with oil spills. An experimental investigation of the feeding strategy of Apple snails from the water free surface, called surface film feeding, is being studied motivated by the need to develop new techniques to recover oil spills. To feed on floating food (usually a thin layer of microorganisms), the apple snail forms a funnel with its foot and pulls the free surface toward the funnel. High speed imaging and particle image velocimetry were used in the present investigation to measure the free surface motion and to investigate the mechanism used by the apple snails to pull the free surface. The results suggest that the snail pulls the free surface via the wavy motion of the muscles in its funnel. [Preview Abstract] |
Tuesday, November 22, 2005 8:52AM - 9:05AM |
LB.00005: Optimizing Snails Eric Lauga, Anette Hosoi Many marine snails propel themselves on a solid surface using travelling waves of surface deformation of their fexible foot. Using fluid forces, these waves allow the force-free organism to move forward, and its velocity is in the direction opposite to the travelling wave (so called ``retrograde motion''). We study the optimization of the travelling wave profile, based on consideration of (1) swimming efficiency, (2) lift force, (3) elastic deformation of the foot and (4) volume of the liquid film. The distinction between real and artificial organisms allows the definition of different optimal snails. [Preview Abstract] |
Tuesday, November 22, 2005 9:05AM - 9:18AM |
LB.00006: Marangoni propulsion by insects David Hu, John Bush Certain water-walking and terrestrial insects can propel themselves on the water surface by generating surface tension gradients. By secreting a surfactant, the water-walker \textit{Microvelia} achieves peak speeds of 17 cm/s, or twice the peak walking speed. We here rationalize peak speeds and present experimental observations that yield insight into this novel form of propulsion. Particular attention is given to elucidating the means by which Marangoni stresses are communicated to the creature across its complex hair covering. [Preview Abstract] |
Tuesday, November 22, 2005 9:18AM - 9:31AM |
LB.00007: The mechanics of cell crawling over a flat surface Baldomero Alonso-Latorre, Javier Rodriguez-Rodriguez, Alberto Aliseda, Rudolf Meili, Richard Firtel, Juan Lasheras We present some recent observations of the motion of cells of the amoeba {\it Dictyostelium Dicoideum} under the effects of a well-controlled linear distribution of chemo-attractant concentration (chemotaxis). The kinematics and dynamics of chemotaxis have been analyzed from microscopy images using a combination of image processing and feature tracking techniques. The trajectory of the cell's center of mass, as well as cell polarization along gradient lines, have been found to follow a quasi-periodic evolution. The frequency of this motion can be related to biochemical processes that are known to be responsible for the internal remodeling of the structure of the cell cytoskeleton and cell motion. The traction force that the cell exerts, through adhesion points, on the substrate has been estimated from the contribution of cell inertia, lubrication layer between the cell and the substrate, and hydrodynamic drag of the flow around the cell. [Preview Abstract] |
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