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Self‐Sharpening Teeth: Self‐Sharpening Mechanism of the Sea Urchin Tooth (Adv. Funct. Mater. 4/2011)
Author(s) -
Killian Christopher E.,
Metzler Rebecca A.,
Gong Yutao,
Churchill Tyler H.,
Olson Ian C.,
Trubetskoy Vasily,
Christensen Matthew B.,
Fournelle John H.,
De Carlo Francesco,
Cohen Sidney,
Mahamid Julia,
Scholl Andreas,
Young Anthony,
Doran Andrew,
Wilt Fred H.,
Coppersmith Susan N.,
Gilbert Pupa U. P. A.
Publication year - 2011
Publication title -
advanced functional materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 6.069
H-Index - 322
eISSN - 1616-3028
pISSN - 1616-301X
DOI - 10.1002/adfm.201190003
Subject(s) - materials science , sharpening , strongylocentrotus purpuratus , composite material , sea urchin , geology , paleontology , computer science , computer vision
The sea urchin tooth is a mosaic of calcite crystals shaped precisely into plates and fibers, cemented together by a robust calcitic polycrystalline matrix. The tooth is formed continuously at one end, while it grinds and wears at the opposite end, the sharp tip. Remarkably, these teeth enable the sea urchin to scrape and bore holes into rock, yet the teeth remain sharp rather than dull with use. Here we describe the detailed structure of the tooth of the California purple sea urchin Strongylocentrotus purpuratus , and focus on the self‐sharpening mechanism. Using high‐resolution X‐ray photoelectron emission spectromicroscopy (X‐PEEM), scanning electron microscopy (SEM), EDX analysis, nanoindentation, and X‐ray micro‐tomography, we deduce that the sea urchin tooth self‐sharpens by fracturing at discontinuities in the material. These are organic layers surrounding plates and fibers that behave as the “fault lines” in the tooth structure, as shown by nanoindentation. Shedding of tooth components at these discontinuities exposes the robust central part of the tooth, aptly termed “the stone”, which becomes the grinding tip. The precise design and position of the plates and fibers determines the profile of the tooth tip, so as the tooth wears it maintains a tip that is continually renewed and remains sharp. This strategy may be used for the top‐down or bottom‐up fabrication of lamellar materials, to be used for mechanical functions at the nano‐ and micrometer scale.