Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session V26: Cellular Biomechanics |
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Sponsoring Units: DBP Room: Baltimore Convention Center 323 |
Thursday, March 16, 2006 11:15AM - 11:27AM |
V26.00001: Difference in cellular mechanics of cancer and normal cervical cells as seen with the AFM Igor Sokolov, Swaminathan Iyer, Venkatesh Subba-Rao, Craig Woodworth Oncogenically transformed cells differ from their normal counter parts in many aspects, including organization and the amount of cytoskeleton. Consequently it is natural to expect to see the difference in cellular mechanics. Here we will present the study of such differences by using atomic force microscopy (AFM) \textit{in-vitro}. So far the present research is the first study of mechanics of cervical cells, and the third comparative study of differences between mechanics of cancer and normal cells down with the help of AFM. Using a micron size silica ball as the AFM probe, we presumably do not overstress the cell surface as it can be in the case of the sharp AFM tip, and consequently, we may use the classical Hertz model. In contrast to the reported previously studies (bladder and fibroblast cells), we found that oncogenically transformed cervical cells are more rigid than the normal cells. The reason for such difference will be discussed. To demonstrate the complexity of the problem, we study cell mechanics in detail. The Young's modulus of rigidity clearly shows two separate regions of rigidity depending on the depth of the probe penetration. There may be two alternative explanations of the difference in rigidity of this top layer: it is either the cell membrane layer or detected long-range (presumably steric) forces due to the molecular ``brush'' of glycocalyx molecules. Experiments and modal calculations will be presented to choose between these two possibilities. [Preview Abstract] |
Thursday, March 16, 2006 11:27AM - 11:39AM |
V26.00002: The Penetration of Titanium Dioxide Nanoparticles: From Dermal Fibroblasts to Skin Tissue Lauren Sipzner, Jaimie Stettin, Zhi Pan, Xiaohua Fang, Wilson Lee, Nadine Pernodet, Miriam Rafailovich TiO2 particles are widely used in industry; however concerns are arising about their penetration into cells and tissue. In this study, we cultured dermal fibroblasts together with different commercial formulations of TiO2 nanoparticles and observed the morphology,traction forces, proliferation, and migration of the cells as a function of nanoparticles dispersion and concentration. The location of the particles within the cell was studied with TEM. We found significant penetration after 30 minutes. In all cases damage to cell structure and function was observed. Actin fibril formation was disturbed, proliferation was severely hindered, and cell motility was impaired. The effects were more pronounced in fibroblasts from older subjects. These effects were attributed to both dimensionality, as well as UV photocatalysis of the particles. The implications for tissues will be discussed. This work is supported by NSF-MRSEC program. [Preview Abstract] |
Thursday, March 16, 2006 11:39AM - 11:51AM |
V26.00003: Curvature-induced microphase separation and lipid polar localization in cell membranes - II Kerwyn Huang, Ranjan Mukhopadhyay, Ned Wingreen In part II of this talk, we discuss how domain sizes in microphase-separated membranes are determined by the physical properties of lipids such as intrinsic curvature in our minimal model for membrane energetics. We then make contact between our model and experiments on the localization of the bacterial phospholipid cardiolipin. We demonstrate that the slight difference in curvature between the poles and midcell region of a micron-sized bacterium is enough to stably localize cardiolipin clusters to the poles, suggesting that cardiolipin clusters could be a target for polarly-localized proteins. We also show that the cardiolipin domain sizes are not sensitive to changes in the membrane composition. Finally, we propose experiments to test our model using inducible expression of cardiolipin in the bacterium \emph{Bacillus subtilis}. [Preview Abstract] |
Thursday, March 16, 2006 11:51AM - 12:03PM |
V26.00004: Curvature-induced microphase separation and lipid polar localization in cell membranes - I Ranjan Mukhopadhyay, Kerwyn Huang, Ned Wingreen Recent research has revealed the prevalence of lipid domains and heterogeneities in biological cell membranes: examples include lipid rafts found in the outer leaflet of eukaryotic plasma membranes and polar localization of the phospholipid, cardiolipin, in bacteria. One of the mysteries has been why domains obsereved in biological cell membranes, such as lipid rafts which are believed to be 10-100 nanometers in size, appear to be much smaller than micron-sized domains observed in model multicomponent lipid vesicles. In this talk we will develop a minimal model for membrane energetics that accounts for the coupling of the bilayer to an elastic substrate such as the actin cortex or cell wall, and will demonstrate how this coupling can lead to microphase separation and formation of stable lipid domains. [Preview Abstract] |
Thursday, March 16, 2006 12:03PM - 12:15PM |
V26.00005: Using Optical Tweezers to Study Cell Mechanics during Airway Reopening Huseyin Yalcin, Jing Wang, Samir Ghadiali, H. Daniel Ou-Yang Patients suffering from the acute respiratory distress syndrome (ARDS) must be mechanically ventilated in order to survive. However, these ventilation protocols may generate injurious hydrodynamic stresses especially during low tidal volume (VT) ventilation when the flow of micron-sized air bubbles displace the surrounding liquid. In-vitro studies in our lab revealed that microbubble flows can severally damage lung epithelial cells (EC). The degree of injury was elevated for sub-confluent monolayers in small channel heights. Under these conditions, the micromechanics of individual EC may influence the degree of cellular injury. To investigate the role of cell mechanics, we used an oscillating Optical Tweezers (OT) technique to measure the intrinsic mechanical properties of EC before and after the flow of microbubbles. Knowledge of how the EC's micromechanical properties influence cell viability may lead to the development of novel treatment therapies that enhance the EC's ability to withstand injurious hydrodynamic stresses during ventilation treatment. [Preview Abstract] |
Thursday, March 16, 2006 12:15PM - 12:27PM |
V26.00006: Probing subcellular force transduction with magnetic soft actuator arrays Alexandre Anguelouch, Stuart Kirschner, Daniel Reich, Nathan Sniadecki, Christopher Chen Microfabricated poly(dimethylsulfoxide) PDMS post arrays provide a method for mapping the distribution of contractile forces produced by adherent cells grown on the tips of the posts through optical tracking of the posts’ deflections (1). We describe a new technique whereby large local mechanical stimuli can be applied to such cells via magnetic torques applied to anisotropic magnetic nanowires embedded in selected posts. These magnetic post arrays thus serve both as actuators and detectors of cellular contractile response. Experiments characterizing the performance of these post arrays will be presented along with results on global changes in cell contractility induced by magnetic forces applied to a single post under a cell. \newline (1) J. Tan {\it et al.} PNAS {\bf 100}, 1484 (2003). [Preview Abstract] |
Thursday, March 16, 2006 12:27PM - 12:39PM |
V26.00007: Establishing threshold toxicity for introducing magnetic nanoparticles into HeLa and HEK 293 cells Kezheng Chen, Weili Luo, Pappachan Kolattukuty Although iron oxide nanoparticles have been suggested as candidate in diverse applications such as drug delivery agents, contrast agents of magnetic resonance imaging, cancer treatment through hyperthermia, etc., the upper limit for safe dosage beyond which the toxicity sets in has never been studied. In this work we report quantitative studies on the percentage change in the number of cell as a function of concentration of magnetic nanoparticles. The incubation is at 37\r{ }C and lasted for 24 hours. We found that there is a critical value of particle volume fraction, above which appreciable number of cell death occurs. This critical value was found to differ in two different cell lines indicating that HEK cells are more robust against the magnetic nanoparticles. [Preview Abstract] |
Thursday, March 16, 2006 12:39PM - 12:51PM |
V26.00008: Modeling cell -- extracellular matrix mechanical interactions during in vitro network formation Daphne Manoussaki During the formation of vascular networks in vitro, endothelial cells exert traction forces onto the extracellular matrix (ECM), changing both the density and the orientation distribution of ECM fibers. ECM strain, in turn, affects cell migration. We study the effect of mechanical cell-ECM interactions on cell migration and cell distribution assuming a continuum description for the cells and the ECM. The theory assumes that the ECM is a viscoelastic material which deforms under cellular traction, and that resulting ECM strain influences cell movement. Numerical simulations predict that under certain mechanical conditions, cell traction can reorganize the cells and associated ECM into a network that compares well with the vascular networks that arise in vitro. I discuss the potential role of cell mechanical forces and ECM mechanical behavior on cell migration, and compare results with in vitro studies. [Preview Abstract] |
Thursday, March 16, 2006 12:51PM - 1:03PM |
V26.00009: Axon growth and dynamics in 3D collagen gels Ryan McAllister, Will Rosoff, Jeffrey Urbach Living cells exhibit importantly different morphology and behavior in 3D hydrogels than on 2D substrates, but there have been very few studies of the dynamics of axons growing in 3D environments. To compare shape and outgrowth behavior of neuronal cells in 2- and 3D, we have developed a live-cell imaging apparatus using a spinning-disk confocal microscope. We compare growth cone cytoskeletal dynamics in fluorescently transfected neuronal cell-lines growing on a coated glass coverslip with those growing in a collagen matrix. We will describe some of the experimental challenges and our results (movies) to date. [Preview Abstract] |
Thursday, March 16, 2006 1:03PM - 1:15PM |
V26.00010: Investigating the glycocalyx using atomic force microscopy Rebecca Boren, Adam Rafi, Jessica Farrell, Antonio Peramo, W. Garrett Matthews The extracellular surfaces of the peripheral vascular system are coated with an outer filamentous layer of proteoglycan (PG) molecules, forming a brush-like structure known as the glycocalyx. The mechanical properties of PGs have become of increased interest due to their roles in a variety of interactions, including the adhesion of metastatic cells and their use as flow sensors. The goal of this project is to investigate the mechanical properties of the glycocalyx as a function of differing environmental conditions (i.e. pH, various ion concentrations, etc). We use as an experimental model of the glycocalyx an end-tethered brush of PGs oriented so that the protein backbone is upright, emulating their \textit{in vivo} formation. We have developed a technique for patterning PG onto substrates allowing the exposure of the PG layer to different biologically relevant solvents. Resulting brush height changes will be measured using atomic force microscopy. The compression and extension of these PG molecules also will be measured and used to explain the imaged structures and the behaviors relevant to their biological function. [Preview Abstract] |
Thursday, March 16, 2006 1:15PM - 1:27PM |
V26.00011: Local structure in diatom biosilica probed by synchrotron x-ray diffraction Michael DiBiccari, Seo-Young Kwak, Geoffrey Hind, Elaine DiMasi Diatoms are single-celled algae that form intricate outer shells, or frustrules, composed of biosilica. They have attracted attention in the context of nanotechnology, since the submicron architectures are genetically determined and thus potentially could be reproduced synthetically, by using organic additives that mimic the proteins responsible for controlling biological silicification. We have compared the local atomic structure of diatom biosilica to that of inorganic silica with synchrotron x-ray diffraction, analyzed as the Pair Distribution Function (PDF). Specimens of Thalassiosira weissflogii (Tw) were cleaned of organic matter using either hydrogen peroxide, commercial bleach, or sodium dodecyl sulfate treatments. Low resolution PDF measurements ($q_{\rm max} \approx 13.6$~\AA$^{-1}$) were made of wet and dry Tw, pure silica microspheres, and diatomaceous earth containing 15\% mineral impurities. All samples have similar PDFs, demonstrating that local structure in diatoms and synthetic silica are equivalent, and that the PDF method is insensitive to biological impurites. [Preview Abstract] |
Thursday, March 16, 2006 1:27PM - 1:39PM |
V26.00012: Bundle Buckling and Nesting Model of Striated Pattern Formation in Microtubule Solutions Yongxing Guo, Yifeng Liu, James Valles, Jay Tang Microtubules that are aligned by magnetic field or flow during the initial stages of polymerization form bundles in high concentration tubulin solutions. These bundles thicken and elongate with time and buckle in coordination with their neighbors into a wave shape. These nested and buckled bundles produce a macroscopically striped pattern of birefringence. We propose a mechanism for the buckling and present a normal mode stability analysis of a simplified model of it. The results show that the characteristic wavelength and critical buckling force are determined by the properties of the bundles and their neighboring elastic network, which is formed by unaligned and relatively short Microtubules. [Preview Abstract] |
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