Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session C65: Biomaterials: Structure, Function, Design IFocus
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Sponsoring Units: DBIO Chair: Suzanne Kane, Haverford College Room: BCEC 260 |
Monday, March 4, 2019 2:30PM - 3:06PM |
C65.00001: Hierarchical biological materials – structure, design and synthesis Invited Speaker: Markus Buehler What if we could design materials that integrate powerful concepts of living organisms - self-organization, the ability to self-heal, tunability, and an amazing flexibility to create astounding material properties from abundant and inexpensive raw materials? This talk will present a review of bottom-up analysis and design of materials for various purposes - as structural materials such as bone in our body or for lightweight composites, for applications as coatings, and as multifunctional sensors to measure small changes in humidity, temperature or stress. These new materials are designed from the bottom up and through a close coupling of experiment and powerful computation as we assemble structures, atom by atom. We review case studies of joint experimental-computational work of biomimetic materials design, manufacturing and testing for the development of strong, tough and smart mutable materials for applications as protective coatings, cables and structural materials. The use of a new paradigm to design materials from the bottom up plays a critical role in advanced manufacturing, providing flexibility, tailorability and efficiency. |
Monday, March 4, 2019 3:06PM - 3:18PM |
C65.00002: The hidden structure of mouse and human enamel Pupa Gilbert Enamel is the hardest and most resilient tissue in the human body. The morphology of human and mouse enamel is well established: it consists of space-filling1, aligned, parallel, ~100 nm wide, microns-long nanocrystals, bundled into 5-micron-wide rods. The orientation and arrangement of enamel crystals, however, are poorly understood yet they confer outstanding materials properties. We show with polarization-dependent imaging contrast (PIC) mapping2,3 that in mouse enamel, within a rod, crystals are co-oriented with one another but not with the long axis of the rod4, in human enamel they are not co-oriented with either: the c-axes of adjacent crystals are most frequently mis-oriented by 1°-30°, and their orientation gradually changes up to 30°-90° within a rod5,6. Molecular dynamics simulations demonstrate that the mis-orientations of adjacent crystals observed in human enamel induce crack deflection6. This toughening mechanism, therefore, contributes to make our enamel last a lifetime. |
Monday, March 4, 2019 3:18PM - 3:30PM |
C65.00003: Does the crystal structure of shark teeth make them stronger? Cayla Stifler, Amber Lim, Benjamin Harpt, Chang-Yu Sun, Pupa Gilbert C. megalodon, a huge ancient shark, was capable of producing bite forces as large as 110,000-180,000 N1. In comparison, great white sharks, a much smaller modern analogue, can only exert a force of 7,400 N when biting1. In both cases, the mechanical stress that the teeth undergo suggests that there might be mesoscale structural features in the fluorapatite crystals in enameloid, which contribute to the superior mechanical properties. Previously, we used PIC (Polarization-dependent Imaging Contrast)2,3 mapping to reveal an intricate woven structure in the fluorapatite crystals in parrotfish enameloid, and hypothesized that this structure contributes to enameloid’s impressive stiffness4. PIC maps from megalodon and great white shark reveal the mesoscale c-axis orientations of enameloid crystals, which contribute to understanding the structure that allows shark teeth to withstand the large bite forces. |
Monday, March 4, 2019 3:30PM - 3:42PM |
C65.00004: Bound-state mobility within the nuclear pore complex Laura Maguire, Michael W Stefferson, M. Betterton, Loren Hough Biopolymeric filters are essential to life. Nuclear transport in particular is an unusual form of filtering in which the flux of select large particles is greatly enhanced over that of smaller nonspecific molecules. The nuclear pore complex, a channel lined with intrinsically disordered FG nucleoporins, facilitates all transport between the nucleus and cytoplasm. It prevents most macromolecules from crossing the nuclear envelope while allowing the passage of transport factors and their cargo. While the basic biochemical interactions leading to transport are well-understood, the detailed mechanism remains a topic of significant debate. We have developed a model of nuclear transport which predicts that nuclear pore selectivity is largely determined by the mobility of FG nucleoporin–transport factor complexes within the pore. We test this prediction by measuring bound-state diffusion of transport factors in tunable nuclear pore mimics which consist of hydrogels filled with FG nucleoporins. Bound-state diffusion is determined for several conditions, including FG nucleoporins of varying length. Bound-state mobility occurs in many biological systems in addition to the nuclear pore complex and could help explain the selectivity of other biopolymeric filters. |
Monday, March 4, 2019 3:42PM - 3:54PM |
C65.00005: Emergence of helical growth in fungal cells from a self-organizing cell wall Franck Vernerey, Shankar Lalitha Sridhar, Revathi Priyanka Mohan, Joseph Ortega Walled cells such as plants, algae and fungi achieve expansive growth using turgor pressure that helps mediate irreversible wall deformation and regulates their shape and volume. The architecture of the cell wall plays a crucial role in this process where a network of microfibrils and tethers (complex polysaccharides and proteins) dynamically mediate the network topology via continuous detachment and reattachment events. A direct consequence of wall architecture, through microfibril re-orientation, is the helical growth of the fungal cells of Phycomyces Blakesleeanus. Powered by turgor pressure and the biochemistry to regulate molecular processes that induce network organization, these cells can control the growth rate and direction of the helix. The relationship between local molecular mechanisms and global emerging behaviors of these cells is still poorly understood. We present a novel approach based in statistical mechanics to model the organization of microfibrils and tethers in the cell wall. The model is then used to predict (a) the longitudinal elongation and rotation rates along the growth zone and (b) the inversion in rotation direction during growth stages in wild-type sporangiophores, and for radial expansion in piloboloid mutants. |
Monday, March 4, 2019 3:54PM - 4:06PM |
C65.00006: Harnessing Design Principles from Glass Sponges for Structurally Robust Lattices Matheus Fernandes, James C Weaver, Katia Bertoldi The glass sponge Euplectella Sp. are predominately deep sea sponges that live in ocean depths of 100-2000m. Beyond their fracture propagation inhibiting material composition, these sponges are perceived to exhibit large structural rigidity and strength against buckling. Since these sponges are primarily made of ’brittle silica’, buckling strength may be a crucial property in making them resistant to impact and environmentally applied stresses. Structurally, they exhibit a base square-grid architecture and regular ordering of vertical and horizontal struts that form the skeletal system. Furthermore, their base structure is overlaid with double diagonal reinforcement struts, which create a checkerboard-like pattern of open-closed cell structure. Based on its similarity to square lattices found in structural engineering, we explore the following research question: Can we generate design principles for diagonal reinforcements of square beam lattices that are optimally designed to avoid global structural buckling? Here, we present a numerical analysis of the structure deformation under various loading conditions as well as survey different arrangements within similar design space of the sponge. Furthermore, we present experimental evidence that supports our numerical analysis. |
Monday, March 4, 2019 4:06PM - 4:18PM |
C65.00007: TOPOLOGICAL PHONONS IN MICROTUBULES: THE LINK BETWEEN LOCAL STRUCTURE AND DYNAMICS OF MICROTUBULES Ssu-Ying Chen, Arooj Aslam, Camelia Prodan, Emil Prodan We have developed a model for analyzing thermal energy propagation through a microtubule by tracking its movement over time, and extracting a phonon spectrum of energy states and the speed of energy propagation through a microtubule. The microtubule is a self-assembling protein structure, and it has been reported that changes in the tubulin proteins that make up the bulk structure of the microtubule can alter its dynamic properties, in particular the polymerization and depolymerization rates. The pathways that dictate how local structure affects system wide dynamics has yet to be elucidated by current measurement techniques. This is because previous methods of defining structural properties of the microtubule hinge on static parameters, such as persistence length and Young's modulus, which neglect the dynamic properties of the microtubule and the anisotropic behavior of these local changes. Our methods look at the vibrational energy propagation through microtubules as an energy source for the energy intensive dynamics of the microtubule. In our methodology, the increased spatial resolution accommodates anisotropy along the length of the microtubule and paves the way for developing a dynamic measurement of microtubule mechanics. |
Monday, March 4, 2019 4:18PM - 4:30PM |
C65.00008: Characterization of fracture in topology-optimized bio-inspired networks Chantal Nguyen, Darin Peetz, Avik Mondal, Ahmed Elbanna, Jean Carlson Trabecular bone is a flexible, lightweight bone tissue that exhibits an anisotropic microarchitecture resembling a web of interconnected struts (trabeculae). We simulate trabecular bone architectures with multi-objective topology optimization, effectively reverse-engineering trabecular structure by optimizing biologically-motivated objectives. Starting from an identical volume, we generate different topologies by varying the objective weights for compliance, surface area, and stability. We model these topologies as disordered, spatially-embedded networks where edges represent trabeculae and nodes represent branch points where trabeculae meet. We simulate mechanical loading on finite-element models where each edge is replaced by a beam, enabling direct comparison of mechanics and topology at multiple scales ranging from that of individual edges/beams to the network at large. We compare the mechanical response of the various topology-optimized networks and identify mechanisms of crack propagation. We characterize and predict crack pathways with community detection methods inspired by similar applications in the study of granular materials. |
Monday, March 4, 2019 4:30PM - 4:42PM |
C65.00009: Coarsening in Coral Skeletons Formation Chang-Yu Sun, László Gránásy, Cayla Stifler, Jun A. Y. Zhang, Tal Zaquin, Tali Mass, Stefano Goffredo, Giuseppe Falini, James C Weaver, Matthew a Marcus, Tamás Pusztai, Pupa Gilbert Spherulites in coral skeletons are composed of acicular aragonite crystals radiating from common centers and exhibiting a 0–35° misorientation of crystallographic c-axes across grain boundaries, previously misattributed entirely to a mechanism called non-crystallographic branching [1,2]. Here, we examine skeletons from 9 diverse species with quantitative nanoscale crystal orientation analyses using Polarization-dependent Imaging Contrast (PIC) mapping [3]. We discovered that, in addition to spherulites, 4 of the species also form tiny (0.2–2 µm), randomly oriented, equant crystals, termed sprinkles. Supported by theoretical phase field simulations, we propose that all initially nucleated crystals are randomly oriented sprinkles, and that these later coarsen, with radially oriented crystals growing at the expense of smaller, randomly oriented sprinkles. This mechanism is analogous to solidification or annealing in metals, both of which are high-temperature phenomena, whereas in coral skeletons coarsening occurs at ambient conditions. |
Monday, March 4, 2019 4:42PM - 5:18PM |
C65.00010: Optical characterization of nacre using hyperspectral imaging Invited Speaker: Mikhail A. Kats Nacre is an organic-inorganic biomineral that lines the inside of shells of various species of mollusks, and comprises layers of aragonite tablets with thicknesses on the order of hundreds of nanometers, bound by an organic protein. The iridescent appearance of nacre results from thin-film interference effects within this layered structure, even though the layers are quite inhomogeneous due to surface roughness, shell curvature, and the disordered nature of the tablets comprising the aragonite layers. |
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