Structural commonalities and deviations in the hierarchical organization of crossed-lamellar shells: A case study on the
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Frédéric Marin UMR CNRS 6282 Biogéosciences, Université de Bourgogne Franche-Comté, 21000 Dijon, France
Stephan E. Wolfa) Department of Materials Science and Engineering, Chair for Glass and Ceramics, Friedrich-Alexander-University Erlangen-Nürnberg, 91058 Erlangen, Germany (Received 18 July 2015; accepted 25 January 2016)
The structural organization of the palliostracum—the dominant part of the shell which is formed by the mantle cells—of Glycymeris glycymeris (Linné 1758) is comprised of five hierarchical levels with pronounced structural commonalities and deviations from other crossed-lamellar shells. The hierarchical level known as second order lamellae, present within other crossedlamellar shells, is absent highlighting a short-coming of the currently used nomenclature. On the mesoscale, secondary microtubules penetrate the palliostracum and serve as crack arrestors. Moreover, the growth lamellae follow bent trajectories possibly impacting crack propagation, crack deflection, and energy dissipation mechanisms whilst circumventing delamination. Finally, at least two structural elements are related to external circatidal and circaanular stimuli. This emphasizes that endogeneous rhythms may contribute and (co-)control the self-organization of a complex mineralized tissue and that it is insufficient to rely fully on a reductionistic approach when studying biomineralization.
I. INTRODUCTION
Biogenic ceramic materials such as nacre feature both remarkable strength and toughness exceeding that of their pure inorganic constituents.1 It is the delicate structural organization across multiple levels of hierarchy which affords biominerals such mechanical properties on the macroscale and renders them an unfathomable source of inspiration for material design. Each level of hierarchy contributes to the macroscale properties and may add a specific key feature on its own characteristic length scale. For instance, biominerals often feature nanogranular organization which adds nanoplasticity to the mineral body thereby toughening it and rendering it insensitive to nanoscaled flaws.2–7 A thorough understanding of such hierarchical systems cannot be accomplished simply by a deconstructive approach as emergent properties may contribute significantly to those on the macroscale. Since it is not possible to generate perfect biomimetic analogues of a highly sophisticated hierarchical composite
Contributing Editor: Michelle L. Oyen a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2016.46 536
J. Mater. Res., Vol. 31, No. 5, Mar 14, 2016
material such as a mollusk shell, a comparative approach contrasting different species could give valuable insights into structure–property relationships, the influence of individual structural motifs, and the self-organization processes by which the formation of the structural motifs are governed. The sophistication of the shell’s organization from the macro- to the nanoscale is owed to an evolutionary pressure imposed by external threats such as predators or ti
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