Tiles stack for shell strength in abalone

Jewelers may prize abalone shells for their mother-of-pearl, but scientists have long been equally enchanted by the shell’s strength. Researchers at the University of California, San Diego have used a novel technique to uncover more of the mollusk’s shell-making secrets.

NATURAL ARMOR. When an abalone shell receives a blow, its stacked tiles slide sideways instead of shattering. University of California, Davis

Reporting in the Jan. 15 Materials Science and Engineering A, Marc André Meyers and Albert Lin examined two species of abalone growing in saltwater tanks. The researchers placed thin glass slides on top of the organisms’ growing shells, which are made of calcium carbonate. Over time, the abalones accepted the glass as part of their shells and deposited new calcium carbonate on top of it. After different time intervals, the researchers removed some of the slides from each organism and examined the newly deposited material with a transmission electron microscope.

As have others, the San Diego scientists observed thousands of calcium carbonate tiles stacked on each other in a bricklike fashion. Each hexagonal-shaped tile is about 10 micrometers across and half a micrometer thick. Lin says that this arrangement of tiles makes the abalone shell far stronger than the calcium carbonate shells of other organisms.

He and his colleagues also found that the sticky protein the mollusks secrete between the layers of tiles isn’t present on the tiles’ edges. This way, if struck by a heavy blow from a predator, the tiles can move sideways instead of shattering. Meanwhile, the glue between layers absorbs the blow’s energy by stretching, says Meyers.

The researchers say that they hope their findings will guide ceramics makers toward stronger materials for products such as body armor.

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