Sea urchins' teeth at the cutting edge of blade technology

AN UNUSUAL characteristic of the humble sea urchin could lead to knives which never need sharpening.

The creatures have self-honing teeth which allow them to chomp through stone, carving out hideaways on rocky shores.

Scientists have learned how the urchins keep their teeth razor-sharp and believe that technology based on the same principle could create "everlasting" bladed tools.

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Analysing the teeth of the California purple sea urchin, the researchers found a complex structure of layered calcite crystals held together by super-hard natural cement.

Between the crystals are layers of weaker organic material. As each hard layer becomes blunt it breaks off, exposing a fresh crystalline surface beneath. In this way, the sea urchin's teeth stay sharp.

Professor Pupa Gilbert, who led the US team from the University of Wisconsin-Madison, said: "The organic layers are the weak links in the chain. 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 crystals come in two forms - plates and fibres - arranged crossways in a tough "biomineral" mosaic.

Prof Gilbert, whose research appears in the journal Advanced Functional Material, added: "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.

"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."