Rock-munching sea urchins have self-sharpening teeth

Sea urchins’ spines aren’t the only sharp part of their prickly bodies. The sea creatures’ five razorlike teeth (above) are self-sharpening—and a new study suggests scientists may be able to harness this power to make cutting-edge tools that rarely require extra honing.

Sea urchins are well known for their ability to chomp through just about anything; they use their small, star-shaped mouths to crunch on brittle starfish, coral reefs, or even rocks. Scientists long suspected the urchins’ ceramic teeth sharpened themselves, but no one could figure out exactly how they did it.

To find out, researchers used scanning electron microscopy to film the teeth of pink sea urchins as they ground against a superhard material made of diamonds. After analyzing 3D movies of exactly how and where the teeth chipped—and conducting multiple mechanical tests—the team found that materials in the teeth are arranged so that they chip only on one side. That helps them maintain a sharp edge all around, they report today in the journal Matter .

On the strong side of the tooth, resilient calcite fibers provide a supportive wall. On the other side, the calcite materials are arranged in brittle inclined plates, which chip away as the tooth scrapes against materials like starfish and rocks, leading to a constantly sharp edge. Sea urchins’ teeth continue to grow throughout their lives, so this wear-and-tear never wears the teeth down too far.

Knowing the material structure of sea urchins’ teeth could help researchers and engineers create drilling or cutting tools that could keep themselves sharp, the researchers say. It wouldn’t be the first time sea urchins’ star-shaped mouths have informed the design of sophisticated tools—in 2016, their five teeth inspired engineers to create a clawlike scoop to help space exploration devices take sediment samples. Putting this new knowledge to use could give engineers of the future something to sink their teeth into.