Making use of materials engineered on the nanoscale is an intriguing approach to medicine. But it’s by no means the end of how nanotechnology might ultimately change medical care. Farther out on the nanomedicine horizon, Carlo Montemagno of Cornell University is working on mechanical devices-motors, pumps, all the equipment for a chemical factory-smaller than a living cell. Nanomotors, for example, might ultimately power small mixers to whip up tiny batches of drugs, then pump out the freshly made pharmaceuticals directly to tissues that need them.
The idea of incorporating motors into your body might seem wild-and it is. But it does have the advantage of being inspired, at least in part, by biology itself. Some bacteria, for instance, move by whipping around a tiny tail, or flagellum. The business end of the flagellum is essentially a motor, and, if you took it apart, you’d see a protein rotor nestled in a pocket formed by six proteins in a ring. Each protein is an enzyme called ATPase, which converts the cellular fuel ATP (adenosine triphosphate) into ADP (adenosine diphosphate); the chemical energy released by this reaction is what powers the machine. When the motor is running, the rotor ratchets around this ring of proteins. Beyond that, biologists actually know little of how the thing functions.
But they do know it works. And to fabricate his nanomotor, Montemagno stole from nature, grafting the moving parts from a bacterial motor onto a metal nanostructure. The Cornell team found a way to attach the nanomotors to an array of tiny pedestals on a micromachined nickel surface. The technique works well enough that Montemagno and his co-workers have demonstrated one of these hybrid motors spinning away: Montemagno’s team is measuring things like horsepower and motor efficiency, tests that would feel right at home to any mechanical engineer scrutinizing a car engine.
Montemagno envisions that tiny chemical factories could one day operate within a cell. He speculates that these nanofactories could be targeted to specific cells, such as those of tumors, where they would synthesize and deliver chemotherapy agents. This selective targeting and local delivery would reduce toxicity to other tissues and pack a much bigger punch than current therapies. One neat trick the group has achieved is to combine the light-harvesting mechanisms from photosynthesis with the biomotor to make a solar-powered nanomachine. Light energy creates ATP, which in turn fuels the nanoengine. It’s the first step to creating autonomous nanodevices that don’t need external fuel sources.
Nanopharmacies like Montemagno’s are at the outer limits of medical technology. It will be years before scientists even know if these nanodevices are practical. But long before that, researchers like Baker hope nanotechnology will be making an impact.
One nearer-term project on Baker’s agenda is smart bombs for treating cancer. These dendrimer-based devices are designed to infiltrate living cells and detect pre-malignant and cancerous changes. If the dendrimer bomb senses such threatening changes, it will release a substance to kill the cell (in one version, laser light is used to trigger the release of chemical agents from the polymer). Just for good measure, when its work is done, the dendrimer device will be able to verify that the cancerous cell is dead.
That may sound just as far out as the nanomotor, but in the eyes of the nation’s preeminent medical researchers, it isn’t. Indeed, last fall, the National Cancer Institute gave Baker’s center $4.4 million to rig up some smart bombs against cancer. Baker hopes to demonstrate the proof of concept in three years. He predicts that in a decade these microscopic SWAT teams will be in the pharmacy. “Being able to engineer things on the scale of biomolecules is very powerful,” he says. So powerful, in fact, that the engineering of the very small could soon pave the way for an entirely different kind of medicine: nanomedicine.