Aitken, Zachary H. and Luo, Shi and Reynolds, Stephanie N. and Thaulow, Christian and Greer, Julia R. (2016) Microstructure provides insights into evolutionary design and resilience of Coscinodiscus sp. frustule. Proceedings of the National Academy of Sciences of the United States of America, 113 (8). pp. 2017-2022. ISSN 0027-8424. PMCID PMC4776537. http://resolver.caltech.edu/CaltechAUTHORS:20160208-125648420
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We conducted in situ three-point bending experiments on beams with roughly square cross-sections, which we fabricated from the frustule of Coscinodiscus sp. We observe failure by brittle fracture at an average stress of 1.1 GPa. Analysis of crack propagation and shell morphology reveals a differentiation in the function of the frustule layers with the basal layer pores, which deflect crack propagation. We calculated the relative density of the frustule to be ∼30% and show that at this density the frustule has the highest strength-to-density ratio of 1,702 kN⋅m/kg, a significant departure from all reported biologic materials. We also performed nanoindentation on both the single basal layer of the frustule as well as the girdle band and show that these components display similar mechanical properties that also agree well with bending tests. Transmission electron microscopy analysis reveals that the frustule is made almost entirely of amorphous silica with a nanocrystalline proximal layer. No flaws are observed within the frustule material down to 2 nm. Finite element simulations of the three-point bending experiments show that the basal layer carries most of the applied load whereas stresses within the cribrum and areolae layer are an order of magnitude lower. These results demonstrate the natural development of architecture in live organisms to simultaneously achieve light weight, strength, and exceptional structural integrity and may provide insight into evolutionary design.
|Additional Information:||© 2016 National Academy of Sciences. Edited by David A. Weitz, Harvard University, Cambridge, MA, and approved January 5, 2016 (received for review October 6, 2015). Published online before print February 8, 2016, doi: 10.1073/pnas.1519790113. We thank the Kavli Nanoscience Institute at Caltech for the availability of cleanroom facilities, Carol Garland for assistance with TEM analysis, and David Z. Chen for assistance with in situ mechanical testing. We also thank Hilde Skogen Chatou at the Norwegian University of Science and Technology (NTNU) for aid in diatom preparation and the NTNU Nanolab for access to the focused ion beam. This work was supported by the Institute for Collaborative Biotechnologies through Grant W911NF-09-0001 from the US Army Research Office. Author contributions: Z.H.A., S.L., C.T., and J.R.G. designed research; Z.H.A., S.L., and S.N.R. performed research; C.T. provided diatom samples; Z.H.A., S.L., and S.N.R. analyzed data; and Z.H.A., S.L., S.N.R., and J.R.G. wrote the paper. The authors declare no conflict of interest. This article is a PNAS Direct Submission. This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1519790113/-/DCSupplemental.|
|Group:||Kavli Nanoscience Institute|
|Subject Keywords:||biomaterials; diatoms; nanoarchitecture; lightweight nanostructure; organic–inorganic composite|
|PubMed Central ID:||PMC4776537|
|Official Citation:||Zachary H. Aitken, Shi Luo, Stephanie N. Reynolds, Christian Thaulow, and Julia R. Greer Microstructure provides insights into evolutionary design and resilience of Coscinodiscus sp. frustule PNAS 2016 113 (8) 2017-2022; published ahead of print February 8, 2016, doi:10.1073/pnas.1519790113|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||George Porter|
|Deposited On:||08 Feb 2016 22:06|
|Last Modified:||13 Apr 2016 21:40|
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