Nanotube strips deliver muscle power.

As animals rely on muscles to move their bodies around, so machines use devices known as actuators for their motions. Now, an international team of researchers has created an actuator that uses carbon nanotubes to mimic muscle fibers. Someday, engineers could incorporate these artificial muscles into robots, aircraft control systems, and sensors, the group says.

Like natural muscles, these devices turn electrochemical energy into mechanical movement. The researchers stick two thin films of matted nanotubes, which they call buckypaper, to double-sided Scotch tape. When they immerse this simple device in saltwater and apply a voltage, the coated tape curves. Reversing the voltage bends the strip in the opposite direction.

Applying a voltage changes the number of electrons in both sheets, causing the nanotubes to expand. However, the nanotubes on the side of the tape that gets positively charged stretch out more than those on the side where negative charge builds up. As a result, the strip bends.

The nanotube actuators work at lower voltages and can generate higher forces than devices made from other materials can, says Ray H. Baughman of AlliedSignal in Morristown, N.J. He and his team report their findings in the May 21 SCIENCE. Ultimately, their goal is to make an actuator for microscopic machines out of a single nanotube (SN: 7/26/97, p. 62). --C.W.