Sea urchin tooth tech could make knives that never go dull 
 
 Sea urchin teeth. Nom nom nom. 
 
 Sea urchins make homes for themselves by chewing through rocks, and the fact that their teeth manage stay sharp while doing this may show us humans how to make self-sharpening knives. 
 
 After literally decades of research, scientists have figured out how sea urchins can eat their way through rocks while keeping their teeth razor sharp. The secret is how the teeth are constructed: layers of calcite biocrystals held together with calcite nanocement are interspersed with softer layers of organic material, and when the teeth start to get dull on the surface, the top organic layer flakes off, exposing a brand new and freshly sharp layer of calcite. Chew, flake, repeat, and you've got infinitely sharp teeth. 
 
 Now that scientists know how the urchins do it, they say that it's at least theoretically possible to create a material with the same properties that could be made into knives and other tools that would sharpen themselves with use. Of course, we can't (yet) make knives that keep growing back like the urchin's teeth do, but at least you'd have something that stayed razor sharp until you wore it down to a nub. 
 
 Science Daily, via Telegraph 
 
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 Sea urchins are perhaps best known for their armor of spines. But their mouths may be even more daunting—urchin teeth can literally chew through stone without getting dull. (Related: "Eyeless Urchins 'See' With Spines.") 
 
 Now scientists are solving the mystery of how urchins keep their teeth so keen, and the research could lead to self-sharpening tools. 
 
 Sea urchins bore through rock to carve out nooks, where they can protect themselves from waves and predators. To learn how urchin teeth stay sharp despite all that grinding, researchers analyzed the roughly 0.8-inch-long (2-centimeter-long) choppers of the California purple sea urchin. 
 
 Using high-resolution x-ray imaging, the investigators found that the teeth are mosaics of two kinds of calcite crystals: fibers and curved plates. The crystal shapes are arranged crosswise to each other and are bound together with a superhard cement of calcite nanoparticles. 
 
 Between the crystals are layers of weaker organic material. By striking the teeth with microscopic, diamond-tipped probes, the scientists found that the teeth break along these organic layers. 
 
 The scientists think the organics are predetermined weak spots in the teeth that allow parts of the material to "tear" away, similar to perforations in a sheet of paper. This means the teeth, which grow continuously, can regularly shed damaged areas to keep a well-honed edge. 
 
 "Such an exquisite structure has evolved over 200 million years, and it can perform far better than manmade, nonoptimized tools," said study co-author Pupa Gilbert, a biophysicist at the University of Wisconsin-Madison. 
 
 "Inspired by these discoveries, we can think of super-robust and fracture-resistant nanocements, or layered nanotips to do nanogrinding that rarely need replacing." 
 
 Much remains uncertain, though, such as the exact composition of the organic layers or the separate functions of the crystalline plates and fibers. 
 
 "Natural biominerals are wonderful, and we have a lot to learn from them," Gilbert said.
– The humble sea urchin may teach us how to make knives that never need to be sharpened. Scientists think they've figured out how the creature manages to eat through rock and still maintain teeth that never go dull, reports National Geographic. "It is one of the very few structures in nature that self-sharpen," says one researcher of each 2-centimeter tooth. Theoretically, scientists could mimic the composition—a complex arrangement of calcite crystals and weaker organic material—for humans tools. Dvice.com sums it up nicely: "The secret is how the teeth are constructed: layers of calcite biocrystals held together with calcite nanocement are interspersed with softer layers of organic material, and when the teeth start to get dull on the surface, the top organic layer flakes off, exposing a brand new and freshly sharp layer of calcite. Chew, flake, repeat, and you’ve got infinitely sharp teeth."