Sea urchin teeth may help toolmakers

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These are the teeth of a sea urchin – and they may eventually help humans manufacture self-sharpening tools.

Sea urchins literally bite their way through stone, using their sharp teeth to bore their way through rocks to excavate a shelter for themselves. 

Despite this constant abrasion with rocks, their teeth remain remarkably sharp and never become dull with use. 

Christopher Killian and co-authors of a paper to be published in a forthcoming issue of the journal Advanced Functional Materials, elucidate the principles behind this self-sharpening mechanism using the teeth of the California purple sea urchin (Strongylocentrotus purpuratus) as a subject in their study.

The authors extracted, fixed, embedded in epoxy and polished sea urchin teeth for analyses of their chemical composition, as well as for studies of their microstructures using advanced microscopy techniques.

The authors found that the sea urchin tooth is a biomineral mosaic of calcite crystals shaped precisely into plates and fibres; this is held together by a polycrystalline matrix composed of calcite and functioning as a nanocement.

Layers of mechanically weaker organic materials are arranged between the calcite plates and fibres, and it is these layers that are the key to the self-sharpening mechanism of the sea urchin tooth. 

The arrangement of the organic material forms predetermined locations that allow the plates and fibres to be broken off and shed in such a manner that exposes a new, sharp cutting edge to the teeth. 

This manner of predetermining breakage is similar in principle to that of perforated paper (as seen in postage stamps).

Our knowledge of the tooth structure in sea urchins may have practical applications for toolmakers. "Now that we know how it works, the knowledge could be used to develop methods to fabricate tools that could actually sharpen themselves with use," according to co-author Pupa Gilbert, who heads the research team. "The mechanism used by the urchin is the key. By shaping the object appropriately and using the same strategy the urchin employs, a tool with a self-sharpening edge could, in theory, be created."

For more information, see the paper: Killian, CE, RA Metzler, Y-T Gong, TH Churchill, IC Olson, V Trubetskoy, MB Christensen, JH Fournelle, F De Carlo, S Cohen, J Mahamid, A Scholl, A Young, A Doran, FH Wilt, SN Coppersmith and PUPA Gilbert (2011) Self-sharpening mechanism of the sea urchin tooth. Advanced Functional Materials DOI: 10.1002/adfm.201001546