Of course, the overarching job of the uniform is to protect the soldier, and the ability to jump from harm’s way or to silently announce oneself to allies would do that indirectly. But the army’s vision is of a suit that would also provide direct protection against everything from bullets to anthrax. Improved ballistic protection is mostly theoretical at this point, but some very real tools against biological and chemical attacks are already in hand.One such technology is based on highly branched polymer molecules called dendrimers. By modifying the ends of a dendrimer’s branches so that each of them sticks to a dangerous molecule and renders it harmless, army researchers have already created a protective substance with great absorptive power for its weight. But so far, they’ve been able to use the substance only by mixing it into a sunblock-like cream. The problem with adding this technology to a soldier’s suit is that dendrimers don’t easily stick to each other and thus are difficult to form into a stable material that would stand up to the abuse of a battlefield-and a washing machine.
To help make a more rugged material, MIT chemical engineer Paula Hammond designed dendrimers with “tails.” These tails, several times longer than the dendrimers’ branches, tend to entangle with one another, keeping the molecules latched together without blocking the branches from doing their jobs. It’s like an extensive root system for a forest of molecular trees, and it could allow the anchored dendrimers to make a tough protective film. “These technologies are just budding right now. We can take them and begin to incorporate them into fabrics and coatings,” Hammond says.
MIT researchers are also working on technologies that could help monitor a soldier’s health remotely, regardless of what hazards he or she might encounter. Built-in sensors that detect changes in body chemistry, for example, might help determine whether a fallen soldier is critically wounded or can wait for aid. Such sensors would have to be extremely sensitive but also robust and simple to operate.
And Swager has made a good first step. Using specially designed polymers as the detector, Swager has recently developed a device to sense concentrations of nitric oxide, a chemical present in human breath. Nitric oxide spikes when the body is stressed (see “Sensing Health,” below). Taken alone, a nitric oxide measurement might not tell the whole story, but the sensor “is a first element that could be part of ways of assessing the physiological state of the soldier,” Swager says.
|A sensor that uses an electrically conducting polymer could directly detect nitric oxide concentrations in a soldier’s breath. Cobalt atoms in the polymer bind and release nitric oxide molecules, causing fluctuations in the resistance of the polymer, which lies between electrodes. (Illustration by John MacNeill)|
The nitric oxide detector uses nanoscopic polymer wires capable of conducting electricity. When nitric oxide binds to the polymer, it produces a change in electrical resistance that can be readily detected. Additionally, the nitric oxide molecules quickly fall off the sensor, giving the device the ability to provide continuous measurements of the chemical’s concentration.
Although just a prototype today, Swager’s device could eventually be incorporated into a mask or the fabric of a soldier’s suit to detect other chemicals-such as hydrocarbons and ketones-that can be indicators of stress or disease, or to detect biological and chemical agents.