Bulletin of the American Physical Society
Annual Meeting of the APS Four Corners Section
Volume 60, Number 11
Friday–Saturday, October 16–17, 2015; Tempe, Arizona
Session B9: Biological Physics I: Cytoskeleton and Mechanobiology |
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Chair: Matthew Green, Arizona State University Room: MU228 |
Friday, October 16, 2015 10:50AM - 11:14AM |
B9.00001: Three dimensional microtubule-based motility assays Invited Speaker: Michael Vershinin Microtubule-based motility in cells is a complex process. Cargos often traverse filament intersections. Such microtubule-microtubule sites may have filaments positioned at various angles and various displacement to each other. The microtubule cytoskeleton and the transport along microtubules are inherently not reducible to a 1D or 2D model. However, to date most in vitro modeling of microtubule-based transport has been in simplified surface-bound assays which are not faithful to the intracellular constraints. I will demonstrate our novel 3D microtubule motility assay in which many microtubules can be independently held and manipulated in 3D. I will also show how we quantify forces exerted by cargos on microtubules during each crossing event and discuss the opportunities this mode of measurement presents for complete modeling of cargo transport. I will discuss progress to date achieved with our in vitro approach. In particular I will show that geometry of the intersection does substantially affect cargo navigation across an individual intersection. [Preview Abstract] |
Friday, October 16, 2015 11:14AM - 11:26AM |
B9.00002: Heterogeneous Force Chains in Cellularized Biopolymer Networks Long Liang, Christopher Allen Rucksack Jones, Daniel Lin, Bo Sun, Yang Jiao Biopolymer Networks play an important role in coordinating and regulating collective cellular dynamics via a number of signaling pathways. Here, we investigate the mechanical response of a biopolymer network due to the active contraction of embedded cells. Specifically, a graph (bond-node) model derived from confocal microscopy data is used to represent the network microstructure, and cell contraction is modeled by applying correlated displacements at specific nodes, representing the focal adhesion sites. A force-based stochastic relaxation method is employed to obtain force-balanced network under cell contraction. We find that the majority of the forces are carried by a small number of heterogeneous force chains emitted from the contracting cells. The mechanisms of the emergence of force chains is discussed, Large fluctuations of the forces along different force chains are observed. Importantly, the decay of the forces along the force chains is significantly slower than the decay of radially averaged forces in the system. These results demonstrated how the fibrous structure of biopolymer network could support long-range force transmission and thus, long-range mechanical signaling between remote cells. [Preview Abstract] |
Friday, October 16, 2015 11:26AM - 11:38AM |
B9.00003: New Model for Deep Indentation by Spherical AFM probes Kiarash Rahmani Eliato, Bryant Doss, Robert Ros Atomic Force Microscopy (AFM) based micro rheology has evolved to a key tool in the study of mechanical properties of biological materials. Spherical indenters and contact mechanic models like the Hertz model are most frequently used for soft materials like cells and hydrogels. However, the Hertz model is limited to shallow indentations due to the model's first order geometry function approximation. Deep indentation provides stiffness information of the sample through its depth. In this work we present a model base on the second-order approximation of sphere geometry and Sneddon's solution for such a geometry. To test this model, polyacrylamide gel were used to collect experimental data both, for quasi-static (e.g. Young's moduli) and dynamic (e.g. Shear Storage and Loss moduli) quantifications. Further, we verified the model by Finite Element Simulations. We found that our model shows constant Young's moduli and more homogenous shear storage moduli through the indentation up to the radius of the probe (e.g. 2.7 \textmu m), while the Young's and shear storage modulus calculated with the Hertz model shows a decrease with the indentation depth. We anticipate that our new model opens the door for accurate deep AFM indentation measurements.. [Preview Abstract] |
Friday, October 16, 2015 11:38AM - 11:50AM |
B9.00004: Quantifying Single Molecule Interactions from Single Cell Force Spectroscopy Data Wayne Christenson, Robert Ros, Ivan Yermolenko, Tatiana Ugarova Single cell force spectroscopy has been demonstrated to be a powerful tool for measuring the maximum adhesion force between a cell and a surface or another cell. We present a method for quantifying specific integrin-ligand interactions on living cells using AFM based SCFS experiments. SCFS data from HEK 293 cells expressing $\alpha $M$\beta $2 leukocyte integrin and wild-type HEK 293 cells on surfaces coated with fibrinogen were analyzed to identify specific ``rupture events.'' High force load ruptures imply a connection of the integrin with the underlying actin cortex of the cell, while low force load ruptures result from the formation of a membrane tether. For highly adhesive fibrinogen surfaces, we found 41{\%} of all rupture events to have a high force load for HEK Mac-1 cells compared to only 9{\%} of rupture events having a high force load for HEK WT data on the same surface. The high force load events in the HEK Mac-1 data showed a median rupture force of 55 pN while HEK WT cells showed a median rupture force of 29 pN. After adding monoclonal antibody directed against the $\alpha $M subunit of the integrin, HEK Mac-1 cells showed similar rupture force values to that of the HEK WT. This analysis demonstrates the ability to quantify specific integrin-ligand interactions. [Preview Abstract] |
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