Issue Date: July 23, 2007
When it comes to engineering materials, there's no match for nature. And many scientists can discover clues, lessons, and even designs from the wondrous constructions of the natural world. New methods to foil counterfeiters could be gleaned from a butterfly's wings. A gecko's foot could hold the secret to super-sticky adhesives.
"One could spend a lifetime trying to understand what nature's designed," says Joanna Aizenberg, a materials science professor at Harvard University. Aizenberg's natural curiosity guides her studies in the intricate structures of sea life, which she emulates with synthetic structures.
Thanks to their evolution-honed design, biological materials often possess superlative properties, she says. They can be fantastically strong or unusually flexible. "Their properties, in the course of evolution, have been perfected," Aizenberg notes. Using natural features as a blueprint, Aizenberg and other scientists can mimic those remarkable properties.
Collected here is a sampling of nature's micro- and nanostructures and, in some cases, the synthetic constructions they've inspired.
Single-celled algae known as coccolithophorids make calcite (CaCO3) structures called coccoliths for protection (below left, 8 µm across). This biomineralization process inspired Aizenberg's group to create an array of uniform synthetic calcite structures (below right, each floret is 3 µm across). The structures may have applications in photonics, composites, and tissue engineering. By studying coccoliths and their synthetic analogs, scientists may learn to control organic-inorganic interactions for these applications.
Densely packed bundles of hairlike setae (below left, 50 µm long) cover the pads of a gecko's feet. The tips of the setae branch out into hundreds of smaller projections, known as spatulae (below right, each tip is 200 nm across). These structures help geckos hang onto walls and ceilings via van der Waals interactions.
Scientists have used diverse materials to make "gecko tapes" that mimic the lizard's remarkable feet. Polyimide gecko tape from Andre Geim's lab at the University of Manchester, in England, is made from a mold created by a lithographic process (below left, each projection is 2 µm long). Ali Dhinojwala at Ohio's University of Akron prepared a gecko tape made of columns of carbon nanotubes that has four times the sticking power of gecko feet (below right, each column is 100 µm wide).
The papilio butterfly's wings are covered with small textured scales (below left, 30µm across). Tiny concavities within these scales (below right, image is 4 µm across) create color through constructive interference, explains Pete Vukusic of the University of Exeter, in England.
In the scales of the green portions of the papilio's wings, the center of the each concavity reflects a bright yellow color, while the edges reflect bright blue (left). To the naked eye, the butterfly appears green. Scientists are trying to mimic these properties for anticounterfeiting applications.
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