Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session F22: Biomaterials I: Paleo and Modern Structure and Function in AnimalsFocus
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Sponsoring Units: DBIO DCP DMP DPOLY Chair: Kristin Bergmann, Massachusetts Institute of Technology MIT Room: 303 |
Tuesday, March 3, 2020 8:00AM - 8:36AM |
F22.00001: The avian eggshell: evolution and engineering of a tough, lightweight biological material Invited Speaker: Mary Caswell Stoddard The eggs laid by modern birds are the products of more than 150 million years of evolution, resulting in a sophisticated package designed to balance a range of competing demands. The egg must be tough enough to prevent external damage but weak enough to permit a chick to hatch. It must resist bacterial contamination but allow gas exchange between the chick and the outside environment. The egg satisfies these requirements, which is remarkable given that it forms in under 24 hours. From an evolutionary perspective, bird eggs are fascinating because they come in a great variety of shapes, sizes, colors, and structures despite the fact that they serve the same essential function: to nourish and protect a chick until it hatches. What selective pressures influence the diversity of egg phenotypes? From an engineering perspective, eggshell is impressive because it is a strong, lightweight material, yet we understand relatively little about eggshell biomechanical properties outside of those from domestic chickens. What is the relationship between the structure and function of eggshell? In addition, how do eggs form in the avian oviduct? Here, we explore these questions through the lenses of evolutionary biology, biophysics and mechanical engineering, which together provide an integrative picture of the form and function of avian eggs. |
Tuesday, March 3, 2020 8:36AM - 8:48AM |
F22.00002: Misorientation and enhanced hardness in tooth enamel Cayla Stifler, Chang-Yu Sun, Elia Beniash, Pupa Gilbert Teeth are subjected to extreme, repetitive forces on a daily basis. Human enamel exerts forces up to 770 Newtons, hundreds of times per day, and must remain functional for decades1. By comparison, great white shark enameloid exerts 7400 Newtons of force when biting, but they shed their teeth regularly2. The mechanical stress the teeth undergo suggests there are structural features in enamel that prevent catastrophic failure. We used PIC (polarization-dependent imaging contrast)3,4 mapping at the calcium L-edge5 to reveal the crystal orientations within rods in mammalian enamel and in bundles in fish enameloid. Analysis of PIC maps from the enamel(oid)6 of diverse animals indicates that c-axis orientations of adjacent crystals are slightly misoriented by small angles. The observed misorientation is positively correlated with the hardness and elastic modulus, suggesting that crystal misorientation is related to, and possibly causes, these enhanced properties. |
Tuesday, March 3, 2020 8:48AM - 9:00AM |
F22.00003: Crystallographic Parameters Of Rod And Interrod Enamel Crystallites Differ Systematically Robert Free, Karen DeRocher, Stuart Stock, Derk Joester Dental enamel has evolved to bear large masticatory forces, resist mechanical fatigue, and withstand wear over decades of use. Functional impairment or loss, as a consequence of developmental defects or tooth decay, has a dramatic impact on health and quality of life. Enamel formation and its degradation remain incompletely understood. This is in part due to its hierarchical architecture. Our objective was to test the hypothesis that crystallographic features of two microstructural features of ename, rod and interod enamel, differ as a consquence of their developmental origin. Towards this goal, we mapped crystallographic order/disorder by azimuthal autocorrelation of WAXS patterns recorded at 500 nm spot size and correlated this information with crystallite size, lattice parameters, and microstrain at each point. We find that there are ystematic variations in these parameters for rod and interrod crystallite populations that suggest differences in composition and imply that there are distinct crystallization environments during amelogenesis. |
Tuesday, March 3, 2020 9:00AM - 9:12AM |
F22.00004: Characterization of a Novel Antimicrobial Agent for Endodontic Applications Aris Zhu, Jeffrey Wolberg, Farzad Koosha, Karena Etwaru, Miriam Rafailovich Recurrent endodontic infections are primarily caused by persistent bacteria Enterococcus faecalis and are more challenging to treat, compared to primary infection of the root canal system. Current treatment, calcium hydroxide (CaOH), is used despite its inefficacy against E faecalis and other common endodontic pathogens, so we developed a more effective composite material named “CASA”. This study characterizes the antimicrobial properties, cytotoxicity, and differentiation potential of CASA for dental pulp stem cells (DPSCs). To determine antimicrobial properties, agar plates were inoculated with common endodontic pathogens. Then, CASA or CaOH was inserted into wells in the agar plate with a diameter of 6 mm. They were incubated for 24 hrs, and then zones of inhibition were measured. CASA produced larger zones of inhibition than CaOH for all species tested. Cytotoxicity studies indicated a high tolerance for DPSCs for CASA, with a measured IC50 of 1.0 mg/ml, a far higher dose than tissue would be exposed to during standard treatment. Addition of 0.25 mg/ml of CASA to DPSCs in osteogenic culture, in the absence of dexamethasone, was observed to hinder differentiation and preserve stemness of the culture. |
Tuesday, March 3, 2020 9:12AM - 9:48AM |
F22.00005: Evolutionary patterns in skeletal biomineralization Invited Speaker: Susannah Porter Mineralized skeletons evolved many times within eukaryotes, providing multiple independent data points for testing hypotheses about skeletal evolution. We have identified >80 acquisitions of mineralized skeletons in eukaryotes along with their time of first appearance and their mineralogy, and have found several interesting patterns. First, the distribution of skeletal mineralogies tends to be non-uniform: most animals and archaeplastidans, for example, chose carbonate, whereas most rhizarians and stramenopiles chose silica. Whether this reflects functional constraints, e.g. related to uni- vs. multicellularity, or phylogenetic constraints, e.g. related to homologous genes involved in nucleation/inhibition of these minerals, is unclear. Second, acquisitions of phosphatic skeletons are clustered in the Cambrian, perhaps due to high PO43- in the oceans at this time. Finally, more than 60% of animal acquisitions occurred in the early Cambrian, whereas those of other eukaryotes are distributed more uniformly in time, supporting the view that factors affecting only animals, e.g., the appearance of carnivores, rather than factors affecting all marine organisms, e.g., increased Ca2+, drove widespread biomineralization in the early Cambrian. |
Tuesday, March 3, 2020 9:48AM - 10:00AM |
F22.00006: Biomineralization by particle attachment in early animals Pupa Gilbert, Susannah M Porter, Chang-Yu Sun, Shuhai Xiao, Brandt M Gibson, Noa Shenkar, Andrew H Knoll Crystallization by particle attachment (CPA)1 of amorphous calcium carbonate (ACC) was demonstrated in modern biominerals from diverse animals. Precisely the same precursors, hydrated and anhydrous ACC, have been observed spectromicroscopically in echinoderms2-4, molluscs5, cnidarians6. This is surprising, as these three phyla have no common ancestor that formed biominerals, and have, therefore, evolved carbonate biomineralization independently ~100 million years after diverging from one another7. Here we correlate the occurrence of CPA of ACC precursor particles with nanoparticulate fabric and then use the latter to investigate the antiquity of the former. SEM images of the oldest known animal biominerals show that these animals used attachment of ACC particles to form their biominerals. The convergent evolution of biomineral CPA may have been dictated by the same thermodynamics and kinetics as we observe today. |
Tuesday, March 3, 2020 10:00AM - 10:36AM |
F22.00007: Applications of molecular taphonomy to the invertebrate fossil record Invited Speaker: Corinne Myers Recently several studies have demonstrated the utility of PhotoEmission Electron spectroMicroscopy (PEEM) to observe exceptional preservation of organic matrix components and shell microstructure in fossil mollusks. Comparisons to modern representatives suggests very strong similarity and potential links to paleoenvironmental conditions (e.g., temperature). Current work must focus on replicating these results across additional time periods and types of biomineralizing species. Future work on the utility of hyperspectral imaging, the geography of preservation, and complementary analyses (e.g., Raman spectroscopy), will provide additional clues into the molecular and structural preservation of biominerals, as well as their evolution through geologic time. |
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