Bulletin of the American Physical Society
2015 Annual Fall Meeting of the APS Ohio-Region Section
Volume 60, Number 12
Friday–Saturday, October 16–17, 2015; Cleveland, Ohio
Session E1: Biological and Medical Physics |
Hide Abstracts |
Chair: Andrew Resnick, Cleveland State University Room: SC311A |
Saturday, October 17, 2015 9:15AM - 9:27AM |
E1.00001: Spiders Tune Glue Viscosity to Maximize Adhesion Gaurav Amarpuri, Ci Zhang, Candido Diaz, Brent Opell, Todd Blacklegde, Ali Dhinojwala Adhesion in humid conditions is a fundamental challenge to both natural and synthetic adhesives. Yet, glue from most spider species becomes stickier as humidity increases. We find the adhesion of spider glue, from five diverse spider species, maximizes at very different humidities, that matches their foraging habitats. By using high-speed imaging we find that the glue viscosity varies over five orders of magnitude with humidity for each species, yet the viscosity at maximal adhesion for each species is nearly identical, 10$^5$-10$^6$ cP. Many natural systems take advantage of viscosity to improve functional response, but spider glue's humidity responsiveness is a novel adaptation that makes the glue stickiest in each species' preferred habitat. This tuning is achieved by hygroscopic organic salts that determine water uptake in the glue. We therefore anticipate that manipulation of hygroscopic salts to control viscosity will provide a simple mechanism to design humidity responsive smart adhesives. [Preview Abstract] |
Saturday, October 17, 2015 9:27AM - 9:39AM |
E1.00002: Mechanical Properties of a Primary Cilium Measured by Resonant Oscillation Andrew Resnick Primary cilia are ubiquitous mammalian cellular substructures implicated in an ever-increasing number of regulatory pathways. The well-established `ciliary hypothesis' states that physical bending of the cilium (for example, due to fluid flow) initiates signaling cascades, yet the mechanical properties of the cilium remain incompletely measured, resulting in confusion regarding the biological significance of flow-induced ciliary mechanotransduction. In this work we measure the mechanical properties of a primary cilium by using an optical trap to induce resonant oscillation of the structure. Our data indicate 1), the primary cilium is not a simple cantilevered beam, 2), the base of the cilium may be modeled as a nonlinear rotatory spring, the linear spring constant `k' of the cilium base calculated to be (4.6 $+$/- 0.62)*10$^{-12}$ N/rad and nonlinear spring constant `$\alpha $' to be (-1 $+$/- 0.34) *10$^{-10}$ N/rad$^{2}$ , and 3) the ciliary base may be an essential regulator of mechanotransduction signalling. Our method is also particularly suited to measure mechanical properties of nodal cilia, stereocilia, and motile cilia, anatomically similar structures with very different physiological functions. [Preview Abstract] |
Saturday, October 17, 2015 9:39AM - 9:51AM |
E1.00003: A Feasibility Study of Extracting Absolute Flow Rates Using Laser Speckle Contrast Imaging Anthony Young, Karthik Vishwanath Laser speckle contrast imaging (LSCI) is a technique that is capable of sensing superficial blood flow in human tissues. This can be used to study effects that diseases such as diabetes and systemic sclerosis have on microvascular blood flow. LSCI quantifies flow rate in arbitrary units by analyzing the fluctuations in the scattered speckle pattern captured from a coherent source incident on a moving medium. In this study the relationship between the LSCI flow units and volumetric flow were investigated. A peristaltic pump was used to flow a solution of water and polystyrene spheres through a flow channel at different flow-rates. LSCI was used to image the flow channel and processed to derive measured flow which were then compared to the absolute flow rates. These LSCI measurements were repeated for varying exposure time. We found that the relationship between the flow rates estimated from LSCI and the absolute flow rate was not linear over the range of flow rates used. As the absolute flow rates increased, the LSCI measurements appeared to be saturated and could not distinguish between different flow rates. [Preview Abstract] |
Saturday, October 17, 2015 9:51AM - 10:03AM |
E1.00004: Validating a Monte Carlo-based Inverse Model for Determination of Absorption and Scattering Properties of Tissue Phantoms Lindsay Darkins, Karthik Vishwanath Diffuse reflectance spectroscopy (DRS) is a non-invasive method to obtain information about a turbid sample using its optical properties. DRS has previously been used in several biomedical applications including diagnosis of normal vs. diseased tissue. A bifurcated optical probe directs light to the sample and collects the reflected light into a spectrometer. The reflectance spectrum is analyzed using an inverse Monte Carlo (MC) model. The model guesses the optical properties of the unknown sample to predict a reflectance spectrum and matches it to the measured reflectance by using reflectance acquired from a reference sample with known optical properties. The optical properties of the unknown sample are adjusted until the error between the modeled and measured reflectance is minimized, which yields the absorption and scattering coefficients. Optical phantoms made with food coloring, hemoglobin, and polystyrene spheres were used to test the inverse MC model. A DRS system was constructed and data collection was controlled by a Raspberry Pi, making this technology portable and practical for clinical settings. The model was able to produce excellent fits of the data, showing that it is working as expected and can be reliably used for later experiments. [Preview Abstract] |
Saturday, October 17, 2015 10:03AM - 10:15AM |
E1.00005: Collateral Sensitivity Networks Limit the Emergence of Drug Resistance via Clonal Interference Jeff Maltas, Victoria Wobster, Zander Galluppi, Kevin Wood Bacterial populations are often comprised of heterogeneous mixtures. Mutants within these populations may confer collateral resistance, or resistance to antibiotics the population has yet to encounter. Interestingly, recent work has focused on the existence of \textit{collateral} \textit{sensitivity, }or increased susceptibility to antibiotics. These studies demonstrate that the evolutionary dynamics of isogenic populations can be controlled via drug-cycling according to collateral sensitivity networks. This raises a complimentary question -- can heterogeneous populations comprised of multiple resistant mutants be controlled by sequential drug administration? Here, we evolved a collateral sensitivity and resistance network for the gram-positive bacteria \textit{Enterococcus faecalis}. Using these networks we were able to demonstrate judicious drug scheduling can significantly reduce overall growth in heterogeneous populations with complimentary drug-susceptibility profiles. While population heterogeneity is often viewed as a bet hedging strategy beneficial to survival, our results indicate collateral sensitivity can be used to limit the emergence of drug resistance by enhancing heterogeneity and facilitating clonal interference between coexisting resistant phenotypes. [Preview Abstract] |
Saturday, October 17, 2015 10:15AM - 10:27AM |
E1.00006: Real-time photo acoustic imaging of potassium in vivo Jeff Folz, Chang Lee, Wuliang Zhang, Raoul Kopelman Potassium ions are of physiological interest due to the role they play in the action potential, electrochemically balancing biological ions, and maintaining a healthy heart. Traditionally, \textit{in vivo} potassium-sensing has been performed using ion-specific electrodes. However, these electrodes are incapable of generating images and are inherently invasive in their application. To address this need, we have developed a potassium sensor suitable for real-time \textit{in vivo }potassium sensing and monitoring. Micelles with nanoscale diameters smaller were loaded with a potassium-binding component and a highly absorptive, low quantum yield pH dye. Changes in potassium concentration induce a measurable pH change within the micelle. Via the photoacoustic effect, the excited dye produces ultrasonic signals that allow us not only to non-invasively monitor potassium's real-time behavior in the body, but also generate images from these changes. Our approach boasts a robust sensing range spanning three orders of magnitude and includes typical intra- and extracellular potassium concentrations. These micelles represent the first demonstration of cationic-analyte imaging and will contribute positively to diagnostic efforts. [Preview Abstract] |
Saturday, October 17, 2015 10:27AM - 10:39AM |
E1.00007: Five-site model for a walking motor protein Jutta Luettmer-Strathmann, Maral Adeli Koudehi, Nabina Paudyal Motor proteins play an important role in many biological processes. For example, kinesin molecules are responsible for the transport of vesicles in nerve cells and their malfunction has been linked to neurodegenerative diseases. Unfortunately, the complexity of motor proteins and their environment makes it difficult to model the detailed dynamics of molecular motors over long time scales. In this work, we develop a simple coarse-grained model for a motor protein on a bead-spring substrate under tension. In our model, pair potentials describe interactions between substrate and motor, motor components, and substrate components. The movement of motor proteins entails ATP hydrolysis, which is modeled in terms of mechano-chemical states that couple positional and chemical degrees of freedom. We apply the model to simulate cargo transport and the pulling of a chain molecule by a motor-protein walker. [Preview Abstract] |
Saturday, October 17, 2015 10:39AM - 10:51AM |
E1.00008: Simulating and Modeling E. Coli's Inorganic Phosphate Two-Component System Response Stephanie Lake Stress on cells, such as nutrient deprivation, can induce signaling processes that amplify further and create necessary proteins simultaneously. Many signaling processes involve low numbers of reactants and thus have stochastic nature. The inorganic phosphate signaling response within E. coli is thought to be one example. Such inherent noise in the system hints to fundamental information behind life processes and survival. The main proteins involved in the phosphate deprivation response in E. coli are the membrane-bound phosphate transporter, Pst, the membrane-bound histidine kinase, PhoR, and the cytoplasmic response regulator, PhoB. When the exterior phosphate concentration falls low, PhoR activates PhoB. Activated PhoB creates a positive feedback loop for the expression of Pst, PhoR, PhoB, and other proteins. Experimental data from changing the exterior phosphate signal suggests there is noise and bistability in expression rate. It is predicted a simple model with seven parameters can be used to represent the system's general behavior. Its structure is based on a birth-death reaction with a hill function acting as the birth rate. The hill function in the experiment relates to the activated state only. An ODE solver and Gillespie's stochastic simulation algorithm were used to simulate the model. The phase space of X and dX/dt were varied and analyzed. The simulations' results were found to be comparable with experimental data. [Preview Abstract] |
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