The flexible circuit also enables a large number of electrodes to be in contact with the skin over a small space—an improvement over current electrodes that typically are individually applied and wired.
And instead of requiring potentially irritating adhesive gel or tape, it takes advantage of nonspecific, generalized adhesion forces, known as van der Waals forces—the same ones that allow geckos to walk up walls. "We're exploiting mechanical processes and geometries to optimize the strength of that adhesion force," Rogers explained in the podcast. "You can put it on like a temporary tattoo, and it will stay there." It stays in place even in the shower, he reports.
In current tests, the patches have stayed on for about a week. Adding some sort of adhesive would probably help seal the deal in the real world, Rogers says. But he likes that the current version shows that external adhesives are "not absolutely required."
Getting power to such a small, flexible patch is a key issue in making it usable. Currently, the team has been able to integrate inductive coils that can pick up power when a nearby primary source operates at high enough levels to power LEDs and other components.
But what happens if someone needs to wear this thing all around town? The next step will be to integrate capacitors or batteries that can store power for later. And borrowing from the already-existing flexible photovoltaic technology, the team is looking toward solar as a possible partner for a built-in battery.
To be a major breakthrough, though, the patch will ultimately need to be entirely wireless. The developers currently rely on small wires that connect to slim ribbon cables to download information, but is already at work integrating wireless radio capabilities.
Like a temporary tattoo, these patches do not cling forever. Rogers pointed out that with the skin's constant renewal, a cycle that takes about two weeks, the patch would need to be replaced. As Zheng notes, the silicon in the new patch is itself part of the device. So "the wafer used for fabrication is not reusable," she says. With her group's mid-layer, the silicon wafer can be used again and again.
Research at Johns Hopkins University has shown that "these devices are not just used to monitor the body but to stimulate it," Rogers said. "The electrical interface works in the other direction as well, so you can stimulate muscle contractions." And being slim and streamlined means that the device "doesn't restrain the motion of the muscle" in the process.
The technology could also some day aid in wound healing, by providing heat or electrical stimulation around a wound. With light integration, the circuits could also be used to assess tissue via spectroscopy.
The device has been attached to subjects' throats as they speak, and using a computer program to recognize patterns, the signals can navigate simple video games with verbal controls. Such communication methods could also be useful for those who suffer from diseases that affect the larynx, as well as possibly controlling prosthetics, Rogers noted.
Rogers hopes that one day they would be able to change the chip's language from that of voltage to one that is more readily understandable to the body, such as fluids and ions. And that would enable interaction "with the tissues at a very deep level," Rogers noted.
In the meantime, mc10 is already working to bring a version of the patch to market. And they have reportedly struck a deal with Reebok to start integrating these sorts of sensors into sportsware.
Although her group could be competing with Rogers's, Zheng says that she is "happy to see that we are working toward the same goal [but] with different approaches."