title: Microstructure provides insights into evolutionary design and resilience of Coscinodiscus sp. frustule.
abstract: 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.
authors: Department of Mechanical and Civil Engineering, California Institute of Technology, Pasadena, CA 91125; zach-aitken@ihpc.a-star.edu.sg.
authors: Zachary H
authors: ZH
authors: Aitken
authors: Division of Engineering and Applied Science, California Institute of Technology, Pasadena, CA 91125;
authors: Shi
authors: S
authors: Luo
authors: Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125;
authors: Stephanie N
authors: SN
authors: Reynolds
authors: Department of Engineering Design and Materials, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway.
authors: Christian
authors: C
authors: Thaulow
authors: Division of Engineering and Applied Science, California Institute of Technology, Pasadena, CA 91125;
authors: Julia R
authors: JR
authors: Greer
mesh_terms: D005075:Biological Evolution; D017377:Diatoms / Q000378:metabolism / Q000648:ultrastructure; D012822:Silicon Dioxide / Q000378:metabolism*
chemical_list: D012822:Silicon Dioxide
keywords: biomaterials; diatoms; lightweight nanostructure; nanoarchitecture; organic–inorganic composite