Skin-mounted electronics that can be applied and worn like a temporary tattoo

Wearable electronics generally take the form of clothing embedded with electronics or miniature electronic devices that can be worn close to the body for purposes such as medical monitoring and communications. Now engineers have developed a device that places electronic components onto an ultra-thin skin-like patch that can be mounted directly onto the skin, paving the way for skin-mounted electronics that could be used for sensing, medical diagnostics, communications and human-machine interfaces.

While the researchers have previously developed thin, flexible silicon electronics on silk substrates that almost completely dissolve when implanted inside the body, the new patches are initially mounted on a thin sheet of water-soluble plastic and are then laminated onto the skin with water, just like applying a temporary tattoo. The researchers say the electronic components could also be applied directly to a temporary tattoo itself to conceal the electronics. Because the circuits are fabricated as tiny, squiggled wires, their wavy, snakelike shape allows then to bend, twist, wrinkle and stretch with the mechanical properties of skin, while maintaining functionality.

The researchers say skin-mounted electronics could be used to replace conventional EEG and EMG sensors for the monitoring of nerve and muscle activity without the need for conductive gel, tape, skin-penetrating pins or bulky wires. They are also more comfortable and less cumbersome than traditional electrodes and give the wearers complete freedom of movement so they can be worn in a natural environment during normal activity.

"If we want to understand brain function in a natural environment, that's completely incompatible with EEG studies in a laboratory," said University of Illinois (U of I) electrical and computer engineering professor Todd Coleman, who co-led the multi-disciplinary team responsible for developing the device. "The best way to do this is to record neural signals in natural settings, with devices that are invisible to the user."

Additionally, skin-mounted electronics could be used to let patients with muscular or neurological disorders to communicate or interface with computers or, when the sensors are applied to the skin of the throat, they can distinguish muscle movement for simple speech. The researchers have already used the electronic patches to control a video game to demonstrate the potential for human-computer interfacing.

The researchers, led by John A. Rogers, the Lee J. Flory-Founder professor of engineering at the U of I, have demonstrated their concept by mounting a variety of electronic components, including sensors, LEDs, transistors, radio frequency capacitors, wireless antennas, and conductive coils and solar cells for power, on a thin, rubbery substrate.

"The blurring of electronics and biology is really the key point here," said Yonggang Huang, a professor at Northwestern University who, with his group, collaborated with Rogers to create the patches. "All established forms of electronics are hard, rigid. Biology is soft, elastic. It's two different worlds. This is a way to truly integrate them."

Because the researchers used simple adaptations of techniques used in the semiconductor industry, they say the patches are easily scalable and manufacturable. Rogers has co-founded a company, mc10, which is already working to commercialize certain versions of the technology.

The researchers are also working to integrate the various devices mounted on the platform so that they work together as a system, instead of as individually functioning devices. They are also working to add Wi-Fi capabilities.

"We think this could be an important conceptual advance in wearable electronics, to achieve something that is almost unnoticeable to the wearer," says Coleman. "The technology can connect you to the physical world and the cyberworld in a very natural way that feels very comfortable."