Science 323, 1575–1578 (2009)

A research team led by Ray Baughman at the University of Texas at Dallas has created an artificial muscle from a ribbon of aerogel — a lightweight, sponge-like material consisting mostly of air — threaded with carbon nanotubes.

Applying a voltage across the width of the ribbon electrically charges the nanotubes; their mutual repulsion can increase the material's width by a factor of three in an instant. A voltage along the length of the ribbon triggers contraction, making the material dense and stiff. The muscles can be turned on and off 1,000 times a second. They can also be 'frozen' at any desired density, which might open up a range of applications depending on the optical and electronic properties of a specific arrangement of nanotubes.