Tuning of Calcite Crystallographic Orientation to Support Brachiopod Lophophore

Citation

Cusack M, Chung P, Zhu W & Endo K (2018) Tuning of Calcite Crystallographic Orientation to Support Brachiopod Lophophore. Advanced Engineering Materials, 20 (9), Art. No.: 1800191. https://doi.org/10.1002/adem.201800191

Abstract
Organisms exert exquisite control on mineral formation by tuning structural and material properties to meet functional requirements. Brachiopods are sessile marine organisms that filter feed via a large lophophore which is supported by a delicate calcite loop that grows from the inner surface of the shell. How does the loop support the weight of the large lophophore? Electron backscatter diffraction (EBSD) and nanoindentation analyses of the loop as it emerges from the shell of Laqueus rubellus reveal that calcite fiber crystallography generates asymmetry in the material properties of the structure. In the core of the emergent loop, the fibers are short and kernel‐like. Either side of the core, the long fibers have a different crystallographic orientation and resultant material properties. fibers on the anterior, load‐bearing side, are harder (H = 3.76 ± 0.24 GPa) and less stiff (E = 76.87 ± 4.87 GPa) than the posterior (H = 3.48 ± 0.31 GPa, E = 81.79 ± 5.33 GPa). As a consequence of the asymmetry in the material properties, the loop anterior may be more flexible under load. The brachiopod strategy of tuning crystallographic orientation to confer spatially determined material properties is attractive for additive manufacturing of synthetic materials that have complex heterogeneous material property requirements.

Keywords
brachiopod; calcite; EBSD; nanoindentation

Journal
Advanced Engineering Materials: Volume 20, Issue 9