Self-Sharpening Tools? Sea Urchins Show How They eat through rocks and keep razor-sharp teeth By John Johnson, Newser Staff Posted Dec 31, 2010 3:02 PM CST 4 comments Comments Shetland sea urchin (Flickr) (Newser) – 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."