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.

Select from the choices above to read the entire article.