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Science 26 January 2007:
Vol. 315. no. 5811, pp. 487 - 490
DOI: 10.1126/science.1135516
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Reports

Reversible Switching of Hydrogel-Actuated Nanostructures into Complex Micropatterns

Alexander Sidorenko,1 Tom Krupenkin,1 Ashley Taylor,1 Peter Fratzl,2 Joanna Aizenberg1*

Responsive behavior, which is intrinsic to natural systems, is becoming a key requirement for advanced artificial materials and devices, presenting a substantial scientific and engineering challenge. We designed dynamic actuation systems by integrating high–aspect-ratio silicon nanocolumns, either free-standing or substrate-attached, with a hydrogel layer. The nanocolumns were put in motion by the "muscle" of the hydrogel, which swells or contracts depending on the humidity level. This actuation resulted in a fast reversible reorientation of the nanocolumns from tilted to perpendicular to the surface. By further controlling the stress field in the hydrogel, the formation of a variety of elaborate reversibly actuated micropatterns was demonstrated. The mechanics of the actuation process have been assessed. Dynamic control over the movement and orientation of surface nanofeatures at the micron and submicron scales may have exciting applications in actuators, microfluidics, or responsive materials.

1 Bell Laboratories/Alcatel-Lucent, Murray Hill, NJ 07974, USA.
2 Max Planck Institute of Colloids and Interfaces, D-14424 Potsdam, Germany.

* To whom correspondence should be addressed. E-mail: jaizenberg{at}alcatel-lucent.com

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