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Rock-Munching Mollusks A Model For Artificial Bones

January 13, 2011

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So that's the latest thinking on a common childhood ailment, and now we're going to explore a scientific question that's more geared toward the elderly: how to make better artificial bones and teeth.

A tiny marine creature might hold the key here. This unexpected possibility comes from a relatively new branch of science called biomaterials. These are materials inspired by what animals and plants make. As NPR's Joe Palca reports, before you can copy what animals do, you have to understand how they do it.

JOE PALCA: If you think about it, it's rather remarkable that creatures with squishy insides like oysters and clams can make rock hard shells and creatures with squishy insides like us can make bones and teeth.

Derk Joester of Northwestern University is interested in how soft things make hard things, so he studies the chiton.

DERK JOESTER: The chiton is a sea creature. It belongs to the mollusks, the bivalves - so the clams and the snails belong to.

PALCA: Chitons are small, rather flat, and oval in shape. The chiton Joester studies is called Chaetopleura apiculata, and it has a rather odd way of getting a meal.

JOESTER: This particular organism literally chews rock in order to feed.

PALCA: It grinds down rock to get at algae and other food particles that might be sandwiched in the rock.

JOESTER: And for that it needs incredibly tough and hard teeth.

PALCA: In fact, Joester says, chiton teeth are one of the hardest and toughest materials known in nature.

JOESTER: They also have a very particular structure that allows them to self-sharpen to a certain degree.

PALCA: A trick Joester would like to be able to replicate in the lab.

JOESTER: Imagine, you know, a knife that keeps its edge forever.

PALCA: But before you can contemplate making such a thing in the lab, you need to know how the chiton does it.

JOESTER: For that we're using one of the most powerful microscopes, the so-called atom probe.

PALCA: He focuses this microscope at the place where the soft organic molecules of the chiton's innards are shaping the rock-hard inorganic minerals of the chiton's teeth.

JOESTER: The microscope really works by plucking a sample apart.

PALCA: Essentially one atom at a time. As he reports in the journal Nature, Joester says they're now getting a better handle on how the chiton uses organic proteins to form tiny pockets that the hard inorganic minerals grow into to make sharp, hard teeth.

Laura Estroff is impressed.

LAURA ESTROFF: This is an unprecedented level of detail.

PALCA: Estroff is a professor of materials science and engineering at Cornell University. When material scientists try to make things in the lab, they frequently have to resort to high temperatures and extreme pressures to force materials into useful shapes. And yet Estroff says the chiton is able to make its remarkable teeth in regular old seawater and with no special equipment. That's why they're worth studying.

Estroff says the key to understanding how they do it is where the soft and hard parts come together.

ESTROFF: Anywhere from mollusk shells to teeth to bone, there's always an organic scaffold upon which the inorganic crystals get grown.

PALCA: She says Joester's atom probe microscope gives a detailed picture of how those scaffolds form.

ESTROFF: What's really cool about this is not only do they image it, but they get composition information as they image it.

PALCA: And that should help scientists take what they learn from how chitons and other creatures make remarkable structures such as shells and teeth and use that to make new biomaterials in the lab.

Derk Joester says it's not all that surprising that primitive creatures like chitons have developed some clever tricks, such as making self-sharpening teeth.

JOESTER: Nature has had 500-odd million years of a head start in product development. And so they have been able to find some really creative and efficient solutions to engineering problems.

PALCA: Engineering problems such as making a better artificial hip joint or a better dental implant.

And if that doesn't work, creating the truly self-sharpening knife would probably be a top seller on late-night television.

Joe Palca, NPR News, Washington.

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