Medical Tattoo Tracks Body Functions
THURSDAY, Aug. 11 -- An invisible patch placed on the skin much like a temporary tattoo can pick up and transmit physiological signals such as heart rate, brain waves and muscle activity.
This new advance in "wearable electronics" might one day replace the bulky wires and electrodes that are routinely used to assess body functions.
"I can't feel its presence," said John Rogers, senior author of a paper on the patch published in the Aug. 12 issue of Science, who demonstrated the two-inch-square device on his forearm during a Wednesday teleconference. "The distinction between electronics and the skin is blurred. It's much like a temporary transfer tattoo, though this has high-quality electronics embedded."
The epidermal electronic system (EES) improves on existing products and processes, many of them borrowed from Silicon Valley and the semiconductor industry.
To make the patch, the researchers first sliced a silicone wafer so thin that it became flexible and floppy like the tissue of the human body, explained Rogers, who is Lee J. Flory Founder Chair in Engineering Innovation at the University of Illinois at Urbana-Champaign.
The wafers were then cut into serpentine shapes so they could also be pulled, stretched and elongated, again to match human biology, then shaped into circuits and bonded to a soft sheet of silicone rubber.
The system is less than the diameter of a human hair.
"We borrowed ideas from the temporary tattoo industry and used a flexible plastic backing that can wash away later," he said.
It also attaches like a temporary tattoo, requiring no separate adhesives or gels. "You [put] it on your skin then just apply water to the backside," Rogers said. "The entire system can have properties similar to the epidermis."
Unlike human skin, though, the EES includes tiny sensors, transmitters and receivers as well as photodetectors, radio frequency indictors and electrophysiological and temperature sensors.
Rogers described a multitude of potential applications.
"These devices are essentially invisible to the person who's wearing them so they can be very easily used for monitoring sleep without disrupting sleep patterns or to monitor premature babies, all kinds of scenarios where adhesive tape and wires are just not suitable," he said.
The system also recognizes words and connects them with muscle movement, which allows the person to speak simple words such as "up," "down," "left" or "right" to direct a computer game.
"This foreshadows the use of technology in more advanced types of human-machine interface -- perhaps most compelling is control of prosthetics," Rogers said.
The same principles could also help people who are limited because of neurological disorders such as amyotrophic lateral sclerosis (ALS) to communicate.
The EES might also form the basis of a "smart" Band-Aid in the future, by using electrical stimulation to accelerate wound healing.
The EES has an antenna, so it is functional. The researchers' next challenge is make all the different elements work as a coherent system, to add Wi-Fi and to figure out the best power sources, such as batteries, wireless coils and solar cells.
"This is not [yet] a fully integrated system with all the bells and whistles we hope to achieve. The story doesn't end here," Rogers said.
"The ultimate goal is to generate commercial products that can be of broad benefit to society," he added. "This paper is a starting point."
Rogers has co-founded a company called mc10, which intends to do exactly that and, he predicts, at reasonable cost.
The company already has a joint development program with Reebok to "introduce these sorts of ideas in sportswear. That's targeted for a product that could launch very soon," Rogers said.
This research was supported in part by the Air Force Research Laboratory and the National Science Foundation.
The American Society of Biomechanics has more on how biology and engineering can work together.
Posted: August 2011
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