Skeleton of Euplectella sp.: Structural Hierarchy from the Nanoscale to the Macroscale
The authors report the robust hierarchical structure of the Euplectella sp. sponge skeleton, and they discuss seven levels of structural hierarchy in the system, from the nano to the macroscale. Comparisons are also drawn to mechanical engineering strategies for strong design that overcomes the limitations of the constituent materials.
Natural material systems can be exceptionally strong and tough despite the inherent mechanical limitations of their constituent materials. Bone, for example, is made of about half organic and half mineral components tightly interconnected at the nanoscale. The hierarchical structure--that is, the structure is different at many different length scales--of collagen fibers and crystallites of calcium phosphate makes it possible for bone to effectively resist fractures. A similar strategy can be observed in mollusk nacre, wherein soft organic layers deflect cracks in calcium carbonate. The most remarkable use of structural hierarchy in nature, however, is arguably in organisms made almost entirely of glass.
Euplectella is a deepwater sponge from the Western Pacific whose glassy skeleton is a hollow cylinder.
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- Figure 1. Two-step soft-lithography process for creating replicas of nanostructured surfaces with high-aspect-ratio features. A) SEM image of an exemplary original nanostructured surface-a silicon master bearing a square array of posts 8mmlong with the diameter 250nmand pitch 2mm. The oblique view is used to best visualize the structure. The insert is an EDS spectrum. B) Liquid PDMS precursor is poured onto the master, treated with an antisticking agent, and cured. C) The curedPDMSis peeled off from the master.D) The negativePDMSmold, which contains an array of high-aspect-ratio wells corresponding to the posts of the positive master, is surface-treated with an antisticking agent. E)SEMimage of thePDMSmold, revealing the high-aspect-ratio wells. F) Liquid precursor (polymer, liquid metal) is poured onto the negativePDMSmold and cured. G) ThePDMS mold is peeled from the cured positive replica. H) SEM image of an exemplary nanostructured replica fabricated from epoxy resin. The insert is an EDS spectrum. The replicated structure is geometrically indistinguishable from the master shown in A).