Interrelated chemical-microstructural-nanomechanical variations in the structural units of the cuttlebone of Sepia officinalis

• Published in: APL materials Vol. 5; no. 11; pp. 116103 - 116103-7
• Main Authors: North, L., Labonte, D., Oyen, M. L., Coleman, M. P., Caliskan, H. B., Johnston, R. E.
• Format: Journal Article
• Language: English
• Published: AIP Publishing LLC 01-11-2017
• ISSN: 2166-532X; 2166-532X
• DOI: 10.1063/1.4993202

“Cuttlebone,” the internalized shell found in all members of the cephalopod family
Sepiidae, is a sophisticated buoyancy device combining high porosity
with considerable strength. Using a complementary suite of characterization tools, we
identified significant structural, chemical, and mechanical variations across the
different structural units of the cuttlebone: the dorsal shield consists of two stiff and
hard layers with prismatic mineral organization which encapsulate a more ductile and
compliant layer with a lamellar structure, enriched with organic matter. A similar
organization is found in the chambers, which are separated by septa, and supported by
meandering plates (“pillars”). Like the dorsal shield, septa contain two layers with
lamellar and prismatic organization, respectively, which differ significantly in their
mechanical properties: layers with prismatic organization are a factor of three stiffer
and up to a factor of ten harder than those with lamellar organization. The combination of
stiff and hard, and compliant and ductile components may serve to reduce the risk of
catastrophic failure, and reflect the role of organic matter for the growth process of the
cuttlebone. Mechanically “weaker” units may function as sacrificial structures, ensuring a
stepwise failure of the individual chambers in cases of overloading, allowing the animals
to retain near-neutral buoyancy even with partially damaged cuttlebones. Our findings have
implications for our understanding of the structure-property-function relationship of
cuttlebone, and may help to identify novel bioinspired design strategies for light-weight
yet high-strength foams.