The key to making the device is what Rogers calls “nanomembrane transistors.” These components are made out thin ribbons of silicon, about 100 nanometers thick; on this scale the material loses its characteristic rigidity and becomes flexible. “It’s much like a piece of two-by-four,” Rogers says. “Wood is not very bendable, but a sheet of paper is.”
Making these transistors required a completely new fabrication technique. Rogers etched out the ribbon circuits from larger blocks of silicon and then used chemical etching to remove silicon from underneath. The circuits could then be peeled away when brought into contact with a stamp-like device.
Once the circuit has been deposited on a substrate, it is encased in a photocurable water-tight epoxy material. This material was difficult to develop, since it had to have the same mechanical properties as the circuit in order to bend with it, but also needed to be resilient enough to prevent any seepage, even at points where the electrodes protrude. “It probably took us half a year to develop a recipe for that,” says Rogers.
The next step, says Litt, is to build a power supply into the device so that it can be used for chronic implantation, and to find a way to transmit data from it wirelessly. The researchers are also developing a version that can also be used to ablate damaged heart tissue through localized heating.
“It is a very impressive advance for electrical mapping of the heart,” says Eric Topol, a cardiologist and director of the Scripps Translational Science Institution, in La Jolla, CA. Today the average ablation procedure for arterial fibrillation takes about three hours at best. “This jump in mapping capability could markedly reduce and simplify these procedures and many other interventions,” he says.