Muscular Nanotubes

Aerogels made from carbon nanotubes (CNTs) can serve as electrically powered artificial muscles, reports a group led by Ray H. Baughman of the University of Texas, Dallas (Science 2009, 323, 1575). Such actuators, which turn electrical energy into mechanical energy, have possible applications in robotics, prosthetic devices, and microscopic pumps. The nanotube aerogel sheets are drawn out of forests of multiwalled CNTs such that the nanotubes line up along the length of the sheet. When a positive voltage is applied to the sheet, the sheet becomes about 220% wider and thicker because of electrostatic repulsive forces. The sheets flex about three orders of magnitude faster and generate more than 30 times the force compared to the same cross-sectional area of natural human muscles. They also work over a wide range of temperatures, from 80 to 1500 K, so they may be most useful in extreme environments such as aerospace applications, Baughman says. Additionally, because the density of the sheets changes as they widen and thicken, they may also have applications as tunable electrodes for applications such as solar cells and organic light-emitting displays.