A Knack For Making Nacre | July 30, 2012 Issue - Vol. 90 Issue 31 | Chemical & Engineering News
Volume 90 Issue 31 | p. 10 | News of The Week
Issue Date: July 30, 2012

A Knack For Making Nacre

Materials Science: Biomimetic route could lead to tough coatings from inexpensive materials
Department: Science & Technology | Collection: Critter Chemistry
News Channels: Materials SCENE
Keywords: nacre, mother of pearl, biomimetic, calcium carbonate
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Nacre made in the lab (right) looks similar to natural nacre on the inside of a shell.
Credit: Alex Finnemore/University of Cambridge
Natural nacre (left) and artificial nacre coated on a slide (10 mm across, right).
 
Nacre made in the lab (right) looks similar to natural nacre on the inside of a shell.
Credit: Alex Finnemore/University of Cambridge

The iridescent gleam of mother-of-pearl couldn’t come from more milquetoast materials. Mollusks make the stuff, also known as nacre, from calcium carbonate and a smattering of organic matter. Despite those simple ingredients, scientists have had a tough time producing the material in the lab. Now, researchers at England’s Cambridge University report a way to make artificial nacre for the first time using CaCO3 as the main component (Nat. Commun., DOI: 10.1038/ncomms1970). The new method could lead to tough coatings from inexpensive starting materials, the scientists say.

Mollusks create nacre by depositing amorphous CaCO3 onto porous layers of the polysaccharide chitin. The mineral then crystallizes, producing stacks of CaCO3 that are separated by layers of organic material. The Cambridge team mimics this process by creating porous organic layers out of poly(acrylic acid) and poly(4-vinylpyridine) onto which amorphous CaCO3 is deposited and subsequently crystallized. The researchers repeat the process to create a multilayered material.

“Essentially, we have created a new recipe for mother-of-pearl using nature’s cookbook,” says Ullrich Steiner, who spearheaded the research. Making the organic material porous was key to reproducing natural nacre’s toughness and iridescence, the researchers report. That’s because the pores provide spots where the CaCO3 crystals can connect the mineral layers.

“While many composite engineering materials outperform nacre, its synthesis entirely at ambient temperatures in an aqueous environment, as well as its cheap ingredients, may make it interesting for coating applications,” notes Alexander Finnemore, who was part of the research team. “Once optimized, the process is simple and can easily be automated,” he says.

“Mimicking the structure and properties of nacre—one of nature’s toughest materials—has been a challenge in materials science for quite a while,” comments Joanna Aizenberg, an expert in biomimetic materials at Harvard University. Steiner’s work represents “a significant step forward in this area,” she says, adding that “the demonstrated ability to form tough surface coatings from cheap base materials by a biomimetic, low-temperature method may hold promise in future materials fabrication approaches.”

 
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