To design prosthetic limbs with motor control and a sense of touch, researchers have been looking at ways to connect electrodes to nerve endings on the arm or leg and then to translate signals from those nerves into electrical instructions for moving the mechanical limb. However, severed nerve cells on an amputated limb can only grow if a structure is present to support them—much the way a trellis supports a growing vine. And they are notoriously fussy about the shape and size of that structure.

"Cells are like people: they like furniture to sit in that's just the right size," says David Martin, a biomedical engineer at the University of Delaware. "They're looking for a channel that's got the 'Goldilocks'-length scale to it—how far apart the ridges are, how tall they are, how [wide] they are."