Many drugs, from anticancer antibodies to hormones, work by activating cell receptors. Once a hormone is in the blood, however, there's no turning it on or off. "This shows that you can turn on and off the signal, and that you can do it instantly," says Christopher Chen, a bioengineer at the University of Pennsylvania. "That's something that's hard to do, for example, with an antibody."

Ingber has many ideas for devices that might integrate his method of cellular control. Magnetic pacemakers could use cells instead of electrodes to send electrical pulses to the heart. Implantable drug factories might contain many groups of cells, each of which makes a different drug when activated by a magnetic signal. Biomagnetic control might lead to computers that can take advantage of cells' processing power. "Cells do complex things like image processing so much better than computers," says Ingber. Ingber, who began the project in response to a call by the Defense Advanced Research Projects Agency for new cell-machine interfaces, acknowledges that his work is in its early stages. In fifty years, however, he expects that there will be devices that "seamlessly interface between living cells and machines."

Other researchers agree. Ingber's biomagnetic control "may represent a new mechanism for man-machine interfaces," says UC San Diego's Chien. But before such interfaces can be developed, says University of Pennsylvania engineer Chen, researchers need to learn a lot more about cells.

"Say we have cells on a chip and we know what behavior we want to elicit," such as getting a stem cell to enter a wound site and initiate repairs, says Chen. "We don't know what signaling events have to happen to put the cell into the right state" so that it will take the desired action.

In the short term, Chen says that Ingber's method could help biologists gain crucial knowledge about cell signaling, such as how these signals are processed chemically and physically by the cell, and how they lead to particular outcomes, from calcium uptake to changes in gene expression. "It provides a tool that lets us tweak the cell and see what happens," says Chen.