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Brewing microscopic skeletons in a beaker.

Zoom in on a drop of pond water and you'll see an extraordinary array of tiny, odd-shaped swimmers encased in intricately patterned outer skeletons. Scientists marvel at those forms, yet stumble in attempts to mimic them.

Now, Geoffrey A. Ozin and Scott Oliver, chemists at the University of Toronto, and their colleagues have found a way to synthesize tiny forms that resemble natural skeletons. They describe the process in the Nov. 2 Nature.

Microorganisms such as diatoms and radiolaria grow the decorative, mineralized outer shells to protect their innards. These exoskeletons display features from 1 micrometer to more than 1 millimeter in size. Ozin's team has managed to synthesize "crystalline, lamellar aluminophosphate structures" on the same scale and with the same subtlety as those seen in nature.

The approach uses both organic and inorganic compounds, which organize themselves into modular patterns on a plain surface. Tiny globules adhering to the growing form, Ozin says, help bowl-shaped textures to emerge. This process helps to minimize free energy on the structure's surface and fosters the accumulation of mineralized honeycomb patterns.

In explaining how the artificial biomineral patterns form, the scientists invoke principles used to describe the formation of natural mineral skeletons. In the case of radiolaria, one model of skeletal formation posits that organisms secrete silica into a network of "bubblelike alveoli." Ozin's group holds that its synthetic structures involve a similar mode of material deposition.

"This work is exciting on two fronts," says Charles T. Kresge, a chemist at the Mobil Strategic Research Center in Princeton, N.J. "There are the materials themselves and the method of synthesizing them." The technique suggests ways to make new catalysts and porous filtration materials, he adds.

Ozin says he found something missing from previous synthetic chemical approaches: "a fourth constructional stage of biomineralization, which controls shape on different scales."

In the 19th century, naturalists marveled at the diversity of nature's skeletal patterns, Ozin says. "Even then, they knew that closely packed cells, minimizing free energy, must create these patterns. The trouble is that no one could replicate this process in a laboratory.

"But these results show that we can almost match nature in the process of turning living materials into stone," he adds, "like Medusa."
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Author:Lipkin, Richard
Publication:Science News
Article Type:Brief Article
Date:Nov 11, 1995
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