Nanoparticle Hydrogel Hybrid

A KEEN SENSITIVITY to their environment allows venus flytraps to ensnare their insect meals. Gently graze their trigger hairs, and the carnivorous plants will clamp together their jawlike leaves. Materials scientists have now managed to replicate this acute environmental sensitivity on the nanometer scale (Science 2007, 315, 487).

Joanna Aizenberg, of Bell Laboratories in Murray Hill, N.J., and coworkers created their own adaptive material by partially covering an array of slender silicon nanocolumns with a layer of flexible hydrogel.

These tiny spikes move in response to changes in humidity. In moist air, water plumps up the hydrogel so that the nanocolumns stand upright. Dry surroundings strip moisture from the hydrogel, making it pull taut across the array, tilting the columns.

By etching patterns onto the array's substrate, Aizenberg's group can choreograph the columns' movement. They can prompt the spikes to snap together in four-pronged snares or to blossom into a field of microflowers.

"Such complex patterned movements would be impossible in the other reported artificial systems, in which polymers are actuated by an electric or magnetic field," Aizenberg says. Potential applications include a coating that's hydrophobic in humid air and hydrophilic in dry air.