Pills and injections serve us well, but for a patient with a chronic illness like diabetes or heart disease, they are less than perfect. Dosages don't always match the body's fluctuating needs, and it's easy to forget to take a pill. But what if doctors could implant a small capsule under your skin that could detect, say, changes in blood sugar levels or some heart disease-related molecule and then release the exact amount of medication needed to keep your illness in check? That's the idea behind a new generation of "smart" drug-delivery devices being worked on by a number of research labs. One of the challenges in making these devices practical is building valves capable of releasing precise amounts of medications from the device's reservoir.

To overcome that hurdle, Ohio State University's Marc Madou, professor of materials science and engineering, is using capsules equipped with tiny muscles. Madou and his group have developed "artificial muscles" that cover microscopic perforations in the 2.5-centimeter-long plastic capsule. The muscles-made of a porous, gel-like polymer-shrink and swell on command, controlling tiny trapdoors that swing shut to cover each perforation. "We got the idea from a kid's toy, those miniature sponges that expand when you drop them in water," says Madou. Apply a negative voltage and the muscles contract, opening the trapdoors and releasing the drug; apply a positive voltage and the muscles expand, shutting the doors and cutting off the flow.