Second in a series of reports on biomedical engineering innovations

Look in any medicine cabinet and you're bound to find a veritable pharmacopeia: tablets, capsules, suppositories, syrups, inhalers, transdermal patches, and maybe even a syringe or two. In 2002 doctors wrote an average of 10.6 prescriptions for each person in the United States. As the population of the industrialized world ages, pharmaceutical companies are struggling to find compounds that ward off—or even reverse—the maladies that historically have plagued aging adults.

But for many of these scourges, the existing means of getting drugs into the body are only moderately effective and may be disruptive or downright painful. For instance, people with adult-onset diabetes—an increasingly common affliction of the middle to later years—suffer more complications if their blood sugar fluctuates widely. Popping pills and injecting insulin a few times a day can lead to peaks and troughs in blood sugar that can wreck small blood vessels, resulting, in the worst instances, in blindness or amputation the feet or lower legs.

Some of the newer drug candidates for treating other illnesses are based on proteins discovered using information gleaned from the human genome. But they can't be taken orally or by injection because stomach acids chew them up or the liver filters them out of the bloodstream too quickly for them to be effective. And many of those wasted molecules are just the ones that aging bodies need to keep them hale and hearty.

To address these problems, electrical engineers are teaming up with gene jockeys and drug developers to invent new drug-delivery systems that marry electronics and semiconductors to biotechnology. Experts agree that new drugs need a degree of intelligence to get where they must go and to arrive on time, and that's where semiconductors come in.

Two approaches are just now being tested for feasibility. One features implantable microchips dotted with tiny drug reservoirs that pop open at the touch of a wireless telemetry button. The other relies on injections of nanometer-scale beads of semiconductors, termed quantum dots, that exploit the energy of electrons to kill cancer cells selectively.

The first disorders to be treated with these "smart" drug-delivery systems will probably be chronic diseases for which patients must take one or more drugs for months or years. Like adult-onset diabetes, many of these maladies—including congestive heart failure—predominantly affect older adults. Research into microchip-based devices, called biological microelectromechanical systems, or bioMEMS, is currently much further along than studies of quantum dots, just now being tested in academic labs as a means for delivering drugs.

In the microchip approach, bioMEMS would be implanted in the body and, ideally, would serve as "closed-loop" systems, holding not only the means to administer a drug but also sensors that could tell when a patient needs another dose. So far, though, only a handful of studies describing bioMEMS-based drug-delivery systems have appeared in peer-reviewed scientific literature, and few companies have such systems in development.

One such company is MicroChips Inc., in Bedford, Mass. At the core of its device is a 15-millimeter silicon microchip that is made using essentially the same techniques for producing integrated circuits. Instead of transistors, however, the device is dotted with 100 tiny reservoirs that are filled with a drug [see illustration, "Silicon Pharmacist"] and [see photo, "Drug Dispenser"]. Each reservoir is capped with a thin layer of platinum and titanium, all of which are fabricated into a network of circuitry that includes patterned gold conductors. It takes just a 4-volt zap to remove an individually addressable well covering, allowing the drug to diffuse out.

Best of all, the whole operation can be triggered by remote control. The bioMEMS unit is stuck to the outside of a sealed titanium case, roughly the size of a pocket watch, that contains a battery, a wireless telemetry chip, and a microprocessor.

MicroChips has been conducting experiments that track the performance of the chips in animals for three months or longer. The drug-dispensing chip and its associated electronics have been implanted under the skin of an animal's shoulder, where the device can be triggered wirelessly. "To administer a dose of drug, we just walk up to the animal and activate the device with a remote control," says John T. Santini Jr., president of MicroChips.