Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session U45: Focus Session: Cell Mechanics II |
Hide Abstracts |
Sponsoring Units: DBIO Chair: Helim Aranda-Espinoza, University of Maryland Room: Hilton Baltimore Holiday Ballroom 4 |
Thursday, March 21, 2013 11:15AM - 11:51AM |
U45.00001: Regulation of Cellular Tension in Adherent Cells Invited Speaker: Patrick Oakes Cells generate stress on their surrounding extracellular matrix (ECM) via myosin II motor generated forces which are transmitted through the actin cytoskeleton. The mechanisms in the cell which regulate the magnitude and spatial distribution of these stresses, however, remain unknown. Consistent with previous reports, we find that the total magnitude of traction force exerted on the ECM scales with cell size. Such scaling is observed across numerous cell types and reflects an inherent cellular tension determined by the level of myosin II activity. Surprisingly, while stiffness modulates the cellular spread area, we find this scaling relationship to be independent of ECM stiffness. To identify the biophysical mechanisms regulating the generation of tension, we utilize micro-patterning to isolate cell spread area from cell geometry and to spatially control the distribution of stress on the ECM. We find that traction stress magnitude is dependent on the local curvature of the cell. Changes in cell geometry result in a redistribution of local stresses, but little change in the total stress applied to the ECM. Finally, for a constant geometry, we find that both the total stress and the average stress exerted on the ECM increase with cell area. Together these data suggest that the cell can be modeled as a uniformly contracting mesh, where the magnitude of tension is regulated by the cell spread area, and the distribution of tension is regulated by local geometry. [Preview Abstract] |
Thursday, March 21, 2013 11:51AM - 12:03PM |
U45.00002: Mechanical Coupling of Smooth Muscle Cells Using Microengineered Substrates and Local Stimulation Craig Copeland, David Hunter, Leslie Tung, Christopher Chen, Daniel Reich Mechanical stresses directly affect many cellular processes, including signal transduction, growth, differentiation, and survival. Cells can themselves generate such stresses by activating myosin to contract the actin cytoskeleton, which in turn can regulate both cell-substrate and cell-cell interactions. We are studying mechanical forces at cell-cell and cell-substrate interactions using arrays of selectively patterned flexible PDMS microposts combined with the ability to apply local chemical stimulation. Micropipette ``spritzing'', a laminar flow technique, uses glass micropipettes mounted on a microscope stage to deliver drugs to controlled regions within a cellular construct while cell traction forces are recorded via the micropost array. The pipettes are controlled by micromanipulators allowing for rapid and precise movement across the array and the ability to treat multiple constructs within a sample. This technique allows for observing the propagation of a chemically induced mechanical stimulus through cell-cell and cell-substrate interactions. We have used this system to administer the acto-myosin inhibitors Blebbistatin and Y-27632 to single cells and observed the subsequent decrease in cell traction forces. Experiments using trypsin-EDTA have shown this system to be capable of single cell manipulation through removal of one cell within a pair configuration while leaving the other cell unaffected. [Preview Abstract] |
Thursday, March 21, 2013 12:03PM - 12:15PM |
U45.00003: Contractile Film Model for Polymorphism in Adherent Cells Shiladitya Banerjee, Luca Giomi The optimal shapes attained by contractile cells on elastic substrates are determined by the crosstalk between intracellular forces and extracellular forces of adhesion. We model an adherent stationary cell as a contractile film bounded by an elastic cortex and connected to the substrate via elastic links. When the adhesion sites are continuously distributed, optimal cell shape is constrained by the adhesion geometry, with a spread area sensitively dependent on the substrate stiffness and contractile tension. For discrete adhesion sites, equilibrium cell shape is convex at weak contractility, while developing local concavities at intermediate values of contractility. Increasing contractility beyond a critical value, controlled by substrate stiffness, cell contour undergoes a discontinuous transition to a star-shaped configuration with cusps and protrusions, accompanied by a region of bistability and hysteresis. [Preview Abstract] |
Thursday, March 21, 2013 12:15PM - 12:27PM |
U45.00004: Unidirectional Contact guidance via surface nanotopography Wolfgang Losert, Xiaoyu Sun, Meghan Driscoll, Can Guven, John Fourkas Unidirectional cell migration plays a key role in many critical physiological processes. Guidance of cells in a preferred direction has been explored in the context of chemotaxis and durotaxis. However, a stable field of gradient within a dynamic range needs to be maintained to achieve persistent unidirectional guidance. Hence the spatial extent of gradient sensing is limited. Contact guidance on the other hand can be achieved on surfaces with large spatial extent without changes in guidance efficiency. However, contact guidance is generally bidirectional. Here we demonstrate that unidirectional guidance efficiency is achievable by nanofabrication of asymmetrically shaped surfaces. We analyze cell velocity and orientation, as well as the dynamic changes in cell shape in response to surface topography. [Preview Abstract] |
Thursday, March 21, 2013 12:27PM - 12:39PM |
U45.00005: Biphasic cell responses on laterally mobile films Andreas Kourouklis, Ronald Lerum, Harry Bermudez The engineering of polymer surfaces or matrices that are capable of controlling cell adhesion has been widely explored. In nearly all of these works, the polymer chains (and ligands) are chemically attached to the underlying substrate, and therefore these systems are inherently static. By contrast, cellular environments such as the extracellular matrix (ECM) are dynamic and remodeled by biochemical reactions and biophysical forces. Borrowing this concept from Nature, we created polymer films by an interfacial self-assembly process, whereby individual chains can exhibit lateral mobility (in-plane diffusive motion). NIH 3T3 fibroblasts seeded on such RGD-presenting polymer films show biphasic responses in spreading and adhesion strength to lateral mobility, with a minimal response for intermediate mobility values. Futhermore, preliminary immuno-staining experiments reveal that the total area of focal adhesions demonstrates a similar biphasic trend to the cellular-scale behaviors. In contrast, actin filaments or stress fibers appear to be unaffected by the substrate lateral mobility. These results show that lateral mobility is an important, although not fully explored aspect of mechano-sensing by cells, and can potentially give new perspectives on cell-ECM interactions. [Preview Abstract] |
Thursday, March 21, 2013 12:39PM - 12:51PM |
U45.00006: Remote, In-Plane Mechanosensing by Cells on Thin Floating Collagen Matrices Hamid Mohammadi, Paul Janmey, Christopher McCulloch The mechanical properties of the extracellular matrix impact many cellular functions but little is known about the contribution of matrix deformations to cellular mechanosensing that extends beyond the immediate cell-matrix interface. We examined remote mechanosensing by developing a cell culture model that employs collagen gels circumferentially supported by nylon mesh frames that float on culture medium. This approach obviates mechanical interference from the underlying rigid foundation of tissue culture plastic and enables assessment of remote, in-plane mechanosensing. With this model we found that 3T3 cells rapidly formed cellular processes whose lengths and number per cell depended on the frame opening size. When the opening sizes were increased (from 200 $\mu$m to 1700 $\mu$m widths) mean cell extension length, mean number of extensions per cell, and the sum of cell extension lengths significantly decreased (40-60{\%}; p \textless\ 0.0001). In grids of 200 $\mu$m and 500 $\mu$m widths, cells sensed the presence of nylon frames because cell-generated deformation fields extended to the grid boundaries while this did not occur in grids of 1700 $\mu$m width. This new model demonstrates the ability of cells to sense remotely, variations of matrix stiffness in the absence of a rigid underlying substrate. [Preview Abstract] |
Thursday, March 21, 2013 12:51PM - 1:03PM |
U45.00007: The Crawling Cell as a Brownian Inchworm Moumita Das, J.M. Schwarz Cell migration is integral to several physiological processes such as immune response, wound healing, tissue formation, fertilization etc. Previous studies, both theoretical and experimental, have attempted to model different aspects of cell migration, including adhesion, protrusion and retraction at the level of single cells, and collective motion at the multicellular level. The entire motility process of a single cell and its ability to navigate a landscape containing obstacles is, however, not well understood. We attempt to address this issue by modeling a single moving cell as a Brownian inchworm composed of two beads attached by a spring that can sense and respond to the mechanical properties and architecture of its environment. The elastic interaction between inchworm and the substrate is modeled by molecular clutches. We study the dynamics of this inchworm in a corrugated potential. In particular we focus on the interplay between confinement and adhesion in the motility of this inchworm. This model may provide important insights on cell movement through a biological maze of other cellular and extracellular structures. [Preview Abstract] |
Thursday, March 21, 2013 1:03PM - 1:15PM |
U45.00008: Frequency- dependent cell responses to an electromagnetic stimulus Toloo Taghian, Abdul Sheikh, Daria Narmoneva, Andrei Kogan External electric field (EF) acting on cells in the ionic environment can trigger a variety of mechanical and chemical cell responses that regulate cell functions, such as adhesion, migration and cell signaling; thus manipulation of EF can be used in therapeutic applications. To optimize this process, realistic studies of EF interaction with cells are essential. We have developed a combined theoretical-experimental approach to study cell response to the external EF in the native configuration. The cell is modeled as a membrane-enclosed hemisphere which is cultured on a substrate and is surrounded by electrolyte. Maxwell's equations are solved numerically (ANSYS-HFSS) to obtain 3D EF distribution inside and near the cell subjected to an external EF. Theoretical results indicate that the cell response is frequency dependent, where at low frequency EF is excluded from the cell interior while EF penetration into the cell increases for higher frequencies. In both regimes the spatial distribution and strength of induced EF in membrane varies with frequency. Experimental results are consistent with theoretical predictions and show frequency-dependent cell response, including both membrane-initiated and intracellular pathway activation and growth factor release. [Preview Abstract] |
Thursday, March 21, 2013 1:15PM - 1:27PM |
U45.00009: Measuring and modeling cellular contact guidance through dynamic sensing of nanotopography Can Guven, Meghan Driscoll, Xiaoyu Sun, John Fourkas, Wolfgang Losert We investigate the shape dynamics of the amoeba Dictyostelium discoideum on nanotopographical gratings. Multiple studies have previously implicated the patterning of focal adhesion complexes (FACs) in contact guidance. However, we observe significant contact guidance of Dictyostelium along ridge-shaped nano- and microtopographic surface features, even though Dictyostelium lacks FACs. We measure the surface contact guidance efficiency, which we calculate from the statistics of cell orientations, as a function of the distance between parallel ridges. Ridges with a spacing of about 1.5 $\mu$m lead to the greatest contact guidance efficiency. We previously observed that Dictyostelium cells exhibit oscillatory shape dynamics. Therefore, we model contact guidance as a resonance between the cell oscillations and the nanogratings. In particular, we model cells as stochastic cellular harmonic oscillators that couple to the periodicity of the ridges. The spatial and temporal scales of the oscillations that best couple to the surface are consistent with those of protrusive dynamics. Our results suggest that the coupling of protrusive dynamics, which are governed by actin dynamics, to surface topography is one possible mechanism for contact guidance. [Preview Abstract] |
Thursday, March 21, 2013 1:27PM - 1:39PM |
U45.00010: Interaction of mechanical and electrical oscillations and sensitivity in a model of sensory hair cell Rami M. Amro, Alexander B. Neiman Sensory hair cells are the first stage in conveying the mechanical stimuli into the electrical signals in auditory and vestibular organs of vertebrates. Experiments showed that hair cells rely on active processes in hair bundles to achieve high selective sensitivity, e.g. due to myosin molecular motors inside stereocilia. In lower vertebrates these active processes result in spontaneous oscillations of hair bundles which can be accompanied by oscillations of the cells' membrane potentials. We use modeling to study how the dynamics of both the membrane potential and the hair bundle interact to produce coherent self-sustained oscillations and how this interaction contributes to the cell's sensitivity to external mechanical perturbations. The model incorporates a mechanical stochastic hair bundle system coupled to a Hodgkin-Huxley type system for the membrane potential. We show that oscillatory regimes result in enhanced sensitivity and selectivity to harmonic stimuli. [Preview Abstract] |
Thursday, March 21, 2013 1:39PM - 1:51PM |
U45.00011: Polyacrylamide scaffolds for studying cellular response to substrate stiffness in three dimensions Keng-hui Lin Recent developments in two-dimensional (2D) culture substrates with tunable stiffness and patterned adhesion ligands have demonstrated that biochemical and mechanical cues regulate the biological functions of living cells. We have extended these cell culture platforms into three dimensions (3D), as in complex biological systems, by producing highly ordered scaffolds of polyacrylamide coated with extracellular matrix proteins. We characterized parameters for the scaffold fabrication. We then grew individual fibroblasts in the identical pores of our scaffolds, examing cellular morphological, cytoskeletal, and adhesion properties. We have observed rich variety of morphologies and anchoring strategies assumed by cells growing on our tunable 3D polyacrylamide scaffolds to demonstrate the richness of cell-mciroenvironment interactions when cell adhesions are not confined to 2D surfaces. [Preview Abstract] |
Thursday, March 21, 2013 1:51PM - 2:03PM |
U45.00012: Cell migration under ultrasound irradiations in micrometer scale Shinya Murakami, Yo Otsuka, Yusuke Oshima, Atsuhiko Hikita, Toshiyuki Mitsui Cell movements, migration play an important role in many physiological processes including cell proliferation and differentiation. C2C12, a line of mouse myoblasts is known to differentiate into osteoblast under appropriate conditions. Therefore, C2C12 cells can be chosen for the differentiation studies. However, the movement of the C2C12's has not been fully investigated although the movements may provide a better understanding of the healing processes of bone repair, regeneration and differentiation. In addition, low intensity ultrasound has been thought and used to promote bone fracture healing although the microscopic mechanism of this healing is not well understood. As a first step, we have investigated single cell migration of C2C12 under optical microscopy with and without ultrasound irradiations. The ultrasound is irradiated from an apex of a sharp needle. The frequency is 1.5 MHz and the power intensity is near 24 mW/cm$^2$. These values were similar to the ultrasound treatment values. In this conference, we will show the influence of the ultrasound irradiation on the cell movement by plotting the mean squared displacement and the velocity autocorrelation function as a function of time. [Preview Abstract] |
Thursday, March 21, 2013 2:03PM - 2:15PM |
U45.00013: Scaffold-independent Patterning of Cells using Magnetic Nanoparticles Suvojit Ghosh, Moanaro Biswas, Subbiah Elankumaran, Ishwar Puri Spatial patterning of cells in vitro relies on direct contact of cells on to solid surfaces. Scaffold independent patterning of cells has never been achieved so far. Patterning of cells has wide applications including stem cell biology, tissue architecture and regenerative medicine besides fundamental biology. Magnetized cells in a suspension can be manipulated using an externally applied magnetic field enabling directed patterning. We magnetized mammalian cells by internalization of superparamagnetic nanoparticles coated with bovine serum albumin (BSA). A magnetic field is then used to arrange cells in a desired pattern on a substrate or in suspension. The control strategy is derived from the self-assembly of magnetic colloids in a liquid considering magnetostatic interactions. The range of achievable structural features promise novel experimental methods investigating the influence of tissue shape and size on cell population dynamics wherein Fickian diffusion of autocrine growth signals are known to play a significant role. By eliminating the need for a scaffold, intercellular adhesion mechanics and the effects of temporally regulated signals can be investigated. The findings can be applied to novel tissue engineering methods. [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