Late last year the U.S. Army went shopping for some new uniforms. It wasn't interested in camouflage jumpsuits and olive drabs or even in better versions of the high-tech gear worn by the troops in Afghanistan. What the army wanted was a lightweight combat uniform capable of stopping bullets and toxins, monitoring a soldier's health, communicating with remote commanders-even enabling superhuman strength. But despite the extravagance of that vision, and even though they were looking to academic research institutions for help, army officials made another key desire clear. As MIT materials scientist Edwin Thomas recalls, they "didn't want just papers in Science or Nature. They wanted real stuff."

Real stuff is exactly what MIT researchers presented last January to a visiting army team. Mechanical engineer Ian Hunter played a video of a twitching piece of black ribbon-an expanding and contracting "artificial muscle" that could, in a combat uniform, form a tourniquet or boost leg strength. Materials scientist Yoel Fink showed off some shimmering optical threads capable of reflecting and absorbing different wavelengths of light with great specificity-a property that could be exploited for remote infrared communication that might, for example, allow soldiers to silently identify themselves to allies at night. Faculty members explained the workings of a microscopic sensor MIT chemist Tim Swager had built, just a few molecules wide, that could sniff a soldier's breath for chemical signs of stress.

Strength

A chief objective of the new institute is to create a combat uniform that has built-in strength-the strength to help a soldier lift heavy objects, to pump cooling fluids through embedded channels or to stiffen around a bleeding wound. Hunter's twitching black ribbon is an early indication that nano materials might be able to deliver that sort of strength.

The ribbon is made of an electroactive polymer that can move or change shape in response to an electrical signal. Researchers have long envisioned using these polymers-which can be 100 times stronger than human muscle-as artificial muscles. But so far, they've proved impractical as musclelike machines, largely because their movements are relatively sluggish and also because they've been able to contract or expand by only a few percent of their length. Human muscle can contract and expand by 20 percent.

In Hunter's and Swager's labs, however, researchers have recently worked together to make great strides toward a material with enough range of motion to be useful. The key is a series of molecules that operate like rods and hinges. Pivoting on the hinges, the rods repel or attract one another when a charge is applied or removed. By attaching millions of these rods and hinges end to end like segments of a folding ruler, the researchers were able to create polymers that lengthen and shorten in response to electrical stimuli (see "Molecular Muscle," below). A film made of these polymers produces musclelike movements. "Within the last few months," says Hunter, "we've doubled the range of motion," approaching that of human muscle cells.

Molecular Muscle

A polymer that contracts and expands as much as human muscle uses molecular "hinges" and "rods." The rods repel and attract one another when a charge is applied (top) and removed (bottom). (Illustration by John MacNeill)