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See Inside January 2008

Material World

Scientists take inspiration from nature and instill novel magnetic properties

Cut your finger, and your body starts mending the wound even before you have had time to go and find a Band-Aid. Synthetic materials are not so forgiving, but Nancy R. Sottos, Scott R. White and their colleagues at the University of Illinois at Urbana-Champaign are looking to change all that. They developed a self-healing plastic that contains a three-dimensional network of microscopic capillaries filled with a liquid healing agent. When the material is cracked, the released fluid is hardened by particles of a catalyst that are also sprinkled throughout. The new material can repair minor cracks up to seven times at each location, improving on the group's previous system (in which the fluid was located in individual pockets) that could repair only one injury at each place.

Another feature of natural organisms that scientists have been seeking to emulate is self-assembly. Benoît Roman and José Bico of the City of Paris Industrial Physics and Chemistry Higher Education Institution used the surface tension of evaporating water droplets to fold flea-size origami cubes, pyramids and other structures. Their work used shapes measuring about a millimeter across cut out of a rubbery polymer a mere 40 to 80 microns thick. Thanks to the way that surface tension scales with size, the technique may be effective for self-assembling micron- or nanometer-scale objects made of thinner sheets of polymer.

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