A small electronic device slapped onto the skin like a temporary tattoo could bring us closer to a future that melds body and machine, a cyborg world where people have cell phones embedded in their throats and Internet browsers literally at their fingertips.
Described in the Aug. 12 Science, the gizmos were developed by researchers looking to create less obtrusive medical monitors for premature babies and other special-needs patients. But the technology’s potential for integrating computers into the human body could be vast.
“This is a huge breakthrough,” says nanoengineer Michael McAlpine of Princeton University. “This goes beyond Dick Tracy calling someone with a cell phone on the wrist. It’s having the wrist itself house the device so it’s always with you.”
Though traditional electronic devices are becoming smaller and more powerful, they are still clunky external objects that must be held in the hand or touched. The new stretchy, wireless electronics promise to seamlessly integrate the body with the surrounding electronic world.
The challenge, says study coauthor John Rogers of the University of Illinois at Urbana-Champaign, was matching typically rigid electrical components to the soft, stretchy and flexible skin. Rogers and his colleagues achieved this by converting brittle silicon to a more forgiving state by making it very thin.
The electronic components — which can include light-emitting diodes, solar cells, transistors and antennae, among other things — were all constructed in a malleable net of wavy S-shapes similar to old-fashioned coiled telephone cords, which allows the circuits to work when stretched in any direction.
The researchers sandwiched these components between two protective layers of polyimide, a type of polymer. These layers sit on top of a rubbery silicone film that adheres to skin with weak chemical bonds. The device can also be applied in a temporary tattoo, which both disguises the grid and makes it stick longer.
Rogers is focused on medical applications for the electronic skin. But the basic building blocks of the system can be configured in many ways for widely different uses, he says.
“I think creative folks out there will think of things we haven’t even contemplated,” Rogers says.
For example, the technology has drawn the interest of security-minded people who might be interested in using the electronics to develop a covert communication system. “CIA and others have been interested,” Rogers says. A tiny hidden patch of electronics on the throat, for instance, could allow two agents to covertly communicate with one another. The electronics could detect and transmit muscle activity that represents words, all without the person making a sound.
The superthin electronic skin wrinkles, puckers and stretches just like the body’s skin, making it less intrusive than the bulky wires and cumbersome electrodes typically used to monitor vital signs.
“You can put these on someone’s skin and they can wrinkle their forehead. They could frown,” says neurologist and bioengineer Brian Litt of the University of Pennsylvania. “The materials science is just wonderful.”
The adhesive electronics pick up signals from people’s heartbeats when stuck on the chest, skeletal muscle activity when stuck on the leg, and brain waves when stuck on the forehead, the researchers report. In the study, signals from the body traveled from the device along a thin wire to a computer.
The patches collected data accurately for up to six hours, and showed no signs of degradation or irritation to the arm, neck, forehead, cheek or chin after 24 hours. The researchers think this life span could be extended, particularly if a strong adhesive is used. But Rogers points out that long-term use of the device is limited because skin cells periodically slough off.
Such devices could serve as conduits between the body and other electronics. In their tests the researchers used electronic skin to control a video game. When stuck on the throat, the device read the electrical activity of muscles as a person spoke the words “up,” “down,” “left,” and “right” to control a computer cursor as it navigated through a maze.
The researchers plan to improve the technology by enabling wireless communication and adding ways to store power. The device already has the capability to get power from wireless coils and solar cells. And in the future, such electronics could be designed to power themselves with stray electromagnetic signals or even energy from body heat.
Stretchable, nonintrusive monitors could be particularly helpful for premature babies, Rogers says. The electrodes and monitors now used to track neonatal babies’ vital signs are large and may irritate fragile newborn skin. Such nonintrusive monitors might also help people undergoing sleep studies. The bulky electrodes that measure brain waves often interfere with the sleep the doctors are trying to measure.
And the potential medical applications of the flexible electronics aren’t limited to monitoring. The electronics could offer better control of prosthetic limbs, ways for people with larynx disease to communicate and new treatments for muscle injuries. Rogers and his collaborators are currently testing whether electrical signals produced by electronic skin can improve muscle function in rats after an injury.
