Thursday, February 19, 2015

`Opihi teeth are toughest biological material in the world.

You always knew `opihi were tough, but this tough? The teeth of this Hawaiian delicacy may be the strongest biological material known.

(Image: Three of the favored Hawaiian limpets At top with green border makaiauli; at right with yellow foot is 'alinalina; and at left with gray foot, is ko'ele. Their scientific names, in order are Cellana exarata, Cellana sandwicensis and Cellana talcosa.)

A new British study, published in the Journal of the Royal Society Interface, says limpet teeth are far stronger than the previous winner, spider silk.

They accomplish this with a unique bit of layering—in the same way that wood gains strength when formed into plywood, or carbon fiber canoes get strength from being laid up in a bed of epoxy. The `opihi teeth are made of extremely thin iron oxide fibers in protein. 

Tests on their teeth exhibit “an absolute material tensile strength that is the highest recorded for a biological material, outperforming the high strength of spider silk currently considered to be the strongest natural material, and approaching values comparable to those of the strongest man-made fibres,” write the authors, Asa H. Barber , Dun Lu , Nicola M. Pugno.

Right up there with carbon fiber, they say.

They “exploit distinctive composite nanostructures consisting of high volume fractions of reinforcing goethite nanofibres within a softer protein phase to provide mechanical integrity when rasping over rock surfaces during feeding,” they write.

Goethite is a form of iron oxide.

“This work demonstrates a high-strength composite found in nature and highlights a design strategy towards strong, engineered composites reinforced with a high volume fraction of nanofibrous material,” the authors write.

`Opihi need tough teeth because of the way they feed—they scrape the algae they eat directly off the rock substrate. The paper’s authors suggest that the example of the `opihi may even be useful in improving human teeth.

“As the limpet tooth is effective at resisting failure owing to abrasion, as demonstrating during rasping of the tooth over rock surfaces, corresponding structural design features are expected to be significant for novel biomaterials with extreme strength and hardness, such as next-generation dental restorations,” they write.

The research was done on the common limpet, which is found in European waters. It is of a different genus and species than Hawai`i’s `opihi, although there’s no reason to believe the tooth structure would be significantly different in our species.

There are four limpets commonly seen in the Islands. They include the three shown in the photo above, plus the less appetizing `opihi `wa or false `opihi, Siphonaria normalis.

© Jan TenBruggencate 2015

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