Looking – and staying – sharp

Researchers explore what goes on inside Aristotle’s lantern.

Five sea urchin tooth tips stacked atop one another within the jaws.

Horacio Espinosa

The masticatory apparatus of a sea urchin – commonly known as Aristotle’s lantern – includes five teeth, each held by a separate jaw in a circular arrangement.

Now, researchers from Northwestern University, US, say they have discovered how those teeth manage to keep themselves sharp.

Rather than simply resisting wear, they are built to chip in a way that helps them to maintain a keen edge – not unlike sharpening a knife by selectively removing material from the cutting edge.

"The material on the outer layer of the tooth exhibits a complex behaviour of plasticity and damage that regulates controlled chipping of the tooth to maintain its sharpness," says Horacio Espinosa, lead author of a paper in the journal Matter.

To make up for the loss of material, he explains, an urchin's teeth continue to grow throughout life.

While the findings are intriguing, Espinosa's primary interest is in understanding the behaviour of natural and synthetic nanomaterials across different scales.

He says the new findings should help to guide the design of microstructure and the selection of material constituents for the design of tools for a range of cutting, grinding, and boring applications.

  1. https://www.sciencedirect.com/science/article/pii/0022098184900522
  2. https://dx.doi.org/10.1016/j.matt.2019.08.015
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