Although there was no electricity flowing from the Berkeley nanowires into the cells, the wires may have influenced the cells' behavior. "Penetration of nanowires into the cells is likely to modify to a certain degree the differentiation of stem cells and, generally, gene expression in the cell," says Nicholas Kotov, a chemical engineer at the University of Michigan. "[The Berkeley] configuration may be particularly interesting for electrically excitable cells," including neurons, says Kotov. Embryonic mouse stem cells grown on the Berkeley nanowires matured into muscle cells, which are electrically active, although Yang says it's impossible to determine whether the conductivity of the wires had anything to do with this development.

Understanding how the diameter of the nanowires affects cell survival could have "substantial fundamental importance," Kotov says, but he adds that their findings also show that the researchers have much yet to learn about the cells' responses to the composition and structure of nanoscale materials. He is developing retinal implants that connect to neurons using carbon nanotubes. (See "This Is Your Brain on Nanotubes.")

Harvard's Lieber cautions that Yang's group has not yet demonstrated an active electrical interface between the cells and nanowires, as he did with neurons and as Kotov and others have done with carbon nanotubes.

Yang says that turning on the electricity is his group's next step. "This is the first preliminary data that these nanowire interfaces with cells are okay," he says. He hopes further research will demonstrate that the nanowires, acting as electrodes and chemical-delivery vehicles, can be used to direct stem-cell fates.