Sea urchins show how to make self-sharpening tools

Tools that sharpen themselves every time they’re used could soon be available, following a discovery about the way sea urchins keep their teeth sharp.

Sea urchins literally eat through stone to create their hiding places – but despite the constant grinding and scraping, their teeth never get dull.

Using microscopy and X-ray examination, a University of Wisconsin-Madison team has established that the sea urchin tooth, which is always growing, is a biomineral mosaic composed of calcite crystals. These appear in two forms – plates and fibers – arranged crosswise and cemented together with super-hard calcite nanocement.

Between the crystals are layers of organic materials that are less strong than the calcite crystals.

“The organic layers are the weak links in the chain,” says professor of physics Pupa Gilbert. “There are breaking points at predetermined locations built into the teeth. It is a concept similar to perforated paper in the sense that the material breaks at these predetermined weak spots.”

The discovery, says Gilbert, could have important practical applications for human 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,” she says.

“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.”