The bedrock of modern medicine is an age-old technology: the pill. For the most part, it works. The drug inside the pill finds its way to whatever part of the body it's meant to treat, and the patient recovers.

But sometimes, oral medications just aren't effective. The medication may interact with other drugs or food. It may break down in the stomach before entering the bloodstream. Or, even more frightening, it may trigger other, bigger problems even as it aims to cure. Recall the painkiller Vioxx, which did wonders for arthritis patients but also raised the risk of heart attack and stroke. Or Baycol, a cholesterol-lowering medication that was linked to dozens of reports of fatal kidney failure. In one way or another, traditional oral medications fail hundreds of thousands of patients each year, according to the U.S. Food and Drug Administration.

For years, researchers have searched for better ways to deliver drugs. The ideal method would administer the right dose to the exact area being treated, whether it's an arthritic knee or a tumor in the lungs. From the patient's perspective, it would be both convenient and unobtrusive—as easy as, if not easier than, taking a pill [see sidebar, "The Push-Pull Method"].

My collaborators and I are pursuing that better way. The implantable drug-delivery device we are developing at the Charles Stark Draper Laboratory, in Cambridge, Mass., and at the Massachusetts Eye and Ear Infirmary (MEEI), in Boston, merges aspects of microelectromechanical systems, or MEMS, with microfluidics, which enables the precise control of fluids on very small scales. Unlike rigid implants, such as pacemakers or titanium hips, our device is a flexible, fluid-filled machine: Stretchy tubes expand and contract, and fluids flow in and out of channels according to a preset rhythm. A tiny pump acts as the machine's heartbeat, and software lets the device adapt to new demands from its environment.

Microscale machines are nothing new, of course. For the last four decades, engineers have built them for a variety of purposes, harnessing the mechanical properties of silicon and the same assembly techniques used to manufacture microchips. The resulting MEMS products now appear in all kinds of consumer electronics, such as air-bag sensors, inkjet printers, and the tiny accelerometers inside Nintendo Wii controllers.

Microsystems may have a much greater impact, however, in biomedical engineering. Engineers and clinicians have dreamed up a whole world of assistive devices that could enhance, sustain, and prolong human life. But these health-care innovators are stymied by one key constraint: the difficulty of making the devices small enough to sit comfortably and unobtrusively inside the body. Microscale systems built not from silicon but from flexible, stretchy polymers could be the answer. And to take that one step further, our implantable device may be the first therapeutic MEMS machine to include the active control of fluids.