Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session Y41: Multi-cellular Systems |
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Sponsoring Units: DBIO Chair: Simon Sponberg, Georgia Institute of Technology Room: 344 |
Friday, March 18, 2016 11:15AM - 11:27AM |
Y41.00001: Tension, cell shape and triple-junction angle anisotropy in the Drosophila germband Monica Lacy, M. Shane Hutson, Christian Meyer, Xena McDonald In the field of tissue mechanics, the embryonic development of Drosophila melanogaster offers many opportunities for study. One of Drosophila's most crucial morphogenetic stages is the retraction of an epithelial tissue called the germband. During retraction, the segments of the retracting germband, as well as the individual germband cells, elongate in response to forces from a connected tissue, the amnioserosa. Modeling of this elongation, based on tissue responses to laser wounding, has plotted the internal germband tension against the external amnioserosa stress, creating a phase space to determine points and regions corresponding to stable elongation. Although the resulting fits indicate a necessary opposition of internal and external forces, they are inconclusive regarding the exact balance. We will present results testing the model predictions by measuring cell shapes and the correlations between cell-edge directions and triple-junction angles. These measures resolve the ambiguity in pinpointing the internal-external force balance for each germband segment. [Preview Abstract] |
Friday, March 18, 2016 11:27AM - 11:39AM |
Y41.00002: Small angle x-ray diffraction through living muscle links the lattice structure to macroscopic material properties Travis Tune, Tom Irving, Simon Sponberg Muscle is a unique hierarchical material composed of millions of molecular motors arranged on filaments in a regular lattice structure. The macroscopic, material behavior of muscle can be characterized by its workloop, a periodically activated force-length curve. Muscle is capable of operating as a spring, motor, brake, or strut, defined by its workloop. We are interested in the multiscale physics of muscle that drive its “energetic versatility” -- the ability of muscle to alter its function. Here we introduce a system of two muscles from the cockroach whose workloops are not explained by our current understanding of the determinants of workloop function (the classic force-length, force-velocity, and twitch response). Differences in material behavior may arise from structural differences in the muscle’s active lattice. Using the BIOCat beam at the Advanced Photon Source at Argonne NL, we tested for differences in the two muscles’ lattice structure. Small-angle x-ray scattering (SAXS) revealed a difference of 4-8% in filament spacing. This difference is large compared to the difference in lattice spacing which is expected from a change in muscle strain alone, and could indicate a difference in lattice spacing is contributing the different workloop behavior of the two muscles. [Preview Abstract] |
Friday, March 18, 2016 11:39AM - 11:51AM |
Y41.00003: Curvature dependent modulation of fish fin stiffness Khoi Nguyen, Ning Yu, Mahesh Bandi, Madhusudhan Venkadesan, Shreyas Mandre Propulsion and maneuvering ability of fishes depends on the stiffness of their fins. However, increasing stiffness by simply adding material to thicken the fin would incur a substantial energetic cost associated with flapping the fin. We propose that fishes increase stiffness of the fin not by building thicker fins, but by geometrically coupling out-of-plane bending of the fin's rays with in-plane stretching of a stiff membrane that connects the rays. We present a model of fin elasticity for ray-finned fish, where we decompose the fin into a series of elastic beams (rays) with springy interconnections (membrane). In one limit, where the membranes are infinitely extensible, the fin's stiffness is no more than the sum of the stiffness of individual rays. At the other limit of an inextensible membrane, fin stiffness reaches an asymptotic maximum. The asymptote value increases monotonically with curvature. We propose that musculature at the base of the fin controls fin curvature, and thereby modulates stiffness. [Preview Abstract] |
Friday, March 18, 2016 11:51AM - 12:03PM |
Y41.00004: ABSTRACT WITHDRAWN |
Friday, March 18, 2016 12:03PM - 12:15PM |
Y41.00005: Three-Dimensional Cell Behavior in Microgels Tapomoy Bhattacharjee, Glyn Palmer, Steven Ghivizzani, Benjamin Keselowsky, W Gregory Sawyer, Thomas Angelini The number of dimensions in which particles can freely move strongly influences the collective behavior that emerges from their individual fluctuations. Thus, in 2D systems of cells in petri-dishes, our growing understanding of collective migration may be insufficient to explain cell behavior in 3D tissues. To study cell behavior in 3D, polymer scaffolds are used. Contemporary designs of 3D cell growth scaffolds enable cell migration and proliferative expansion by incorporating of degradable motifs. Matrix degradation creates space for cells to move and proliferate. However, different cell types and experimental conditions require the design of different scaffolds to optimize degradation with specific cell behaviors. By contrast, liquid like solids made from packed microgels can yield under cell generated stresses, allowing for cell motion without the need for scaffold degradation. Moreover, the use of microgels as 3D culture media allows arranging cells in arbitrary structures, harvesting cells, and delivering drugs and nutrients. Preliminary data describing cell behavior in 3D microgel culture will be presented. [Preview Abstract] |
Friday, March 18, 2016 12:15PM - 12:27PM |
Y41.00006: Frequency-dependent micromechanics of cellularized biopolymer networks Chris Jones, Jihan Kim, David McIntyre, Bo Sun Mechanical interactions between cells and the extracellular matrix (ECM) influence many cellular behaviors such as growth, differentiation, and migration. These are dynamic processes in which the cells actively remodel the ECM. Reconstituted collagen gel is a common model ECM for studying cell-ECM interactions \textit{in vitro} because collagen is the most abundant component of mammalian ECM and gives the ECM its material stiffness. We embed micron-sized particles in collagen and use holographic optical tweezers to apply forces to the particles in multiple directions and over a range of frequencies up to 10 Hz. We calculate the local compliance and show that it is dependent on both the direction and frequency of the applied force. Performing the same measurement on many particles allows us to characterize the spatial inhomogeneity of the mechanical properties and shows that the compliance decreases at higher frequencies. Performing these measurements on cell-populated collagen gels shows that cellular remodeling of the ECM changes the mechanical properties of the collagen and we investigate whether this change is dependent on the local strain and distance from nearby cells. [Preview Abstract] |
Friday, March 18, 2016 12:27PM - 12:39PM |
Y41.00007: Asymmetries arising from the space-filling nature of vascular networks David Hunt, Van Savage Cardiovascular networks span the body by branching across many generations of vessels. The structural features of the network that accomplish this density and ubiquity of capillaries are often called space-filling. Some strategies do not lead to biologically adaptive structures, requiring too much construction material or space, delivering resources too slowly, or using too much power to move blood through the system. We empirically measure the structure of real networks to compare with predictions of model networks that are space-filling and constrained by a few guiding biological principles. We devise a numerical method that enables the investigation of space-filling strategies and determination of which biological principles influence network structure. Optimization for only a single principle creates unrealistic networks that represent an extreme limit of the possible structures that could be observed in nature. We first study these extreme limits for two competing principles, minimal total material and minimal path lengths. We combine these two principles and enforce various thresholds for balance in the network hierarchy, which provides a novel approach that highlights the trade-offs faced by biological networks and yields predictions that better match empirical data. [Preview Abstract] |
Friday, March 18, 2016 12:39PM - 12:51PM |
Y41.00008: Spatio-temporal Model of Xenobiotic Distribution and Metabolism in an in Silico Mouse Liver Lobule Xiao Fu, James Sluka, Sherry Clendenon, James Glazier, Jennifer Ryan, Kenneth Dunn, Zemin Wang, James Klaunig Our study aims to construct a structurally plausible in silico model of a mouse liver lobule to simulate the transport of xenobiotics and the production of their metabolites. We use a physiologically-based model to calculate blood-flow rates in a network of mouse liver sinusoids and simulate transport, uptake and biotransformation of xenobiotics within the in silico lobule. Using our base model, we then explore the effects of variations of compound-specific (diffusion, transport and metabolism) and compound-independent (temporal alteration of blood flow pattern) parameters, and examine their influence on the distribution of xenobiotics and metabolites. Our simulations show that the transport mechanism (diffusive and transporter-mediated) of xenobiotics and blood flow both impact the regional distribution of xenobiotics in a mouse hepatic lobule. Furthermore, differential expression of metabolic enzymes along each sinusoid’s portal to central axis, together with differential cellular availability of xenobiotics, induce non-uniform production of metabolites. Thus, the heterogeneity of the biochemical and biophysical properties of xenobiotics, along with the complexity of blood flow, result in different exposures to xenobiotics for hepatocytes at different lobular locations. [Preview Abstract] |
Friday, March 18, 2016 12:51PM - 1:03PM |
Y41.00009: Modeling Oxygen Transport in the Human Placenta Alexander Serov, Marcel Filoche, Carolyn Salafia, Denis Grebenkov Efficient functioning of the human placenta is crucial for the favorable pregnancy outcome. We construct a 3D~model of oxygen transport in the placenta based on its histological cross-sections. The model accounts for both diffusion and convention of oxygen in the intervillous space and allows one to estimate oxygen uptake of a placentone. We demonstrate the existence of an optimal villi density maximizing the uptake and explain it as a trade-off between the incoming oxygen flow and the absorbing villous surface. Calculations performed for arbitrary shapes of fetal villi show that only two geometrical characteristics~- villi density and the effective villi radius~- are required to predict fetal oxygen uptake. Two combinations of physiological parameters that determine oxygen uptake are also identified: maximal oxygen inflow of a placentone and the Damk\"ohler number. An automatic image analysis method is developed and applied to 22~healthy placental cross-sections demonstrating that villi density of a healthy human placenta lies within~10\% of the optimal value, while overall geometry efficiency is rather low~(around~30-40\%). In a perspective, the model can constitute the base of a reliable tool of post partum oxygen exchange efficiency assessment in the human placenta. [Preview Abstract] |
Friday, March 18, 2016 1:03PM - 1:15PM |
Y41.00010: ABSTRACT WITHDRAWN |
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