August 12, 2011
‘Tattoo’ Patch Breakthrough In Health Monitoring
Scientists have developed a new micro-electronics technology that allows an "electronic tattoo" to monitor the vital signs of hospital patients, representing a radical improvement over existing medical monitoring equipment, according to a study published Thursday in the journal Science.
The researchers successfully used the tiny, wireless patch, which includes a sensor that attaches to the skin, to monitor patients' heart and brain activity. The device, which is thinner than a human hair and resembles a temporary tattoo, can move, wrinkle and stretch without breaking.
Such equipment can be "distressing" for some people, such as heart patients, who have to wear a cumbersome monitor for up to a month "in order to capture abnormal but rare cardiac events," the scientists said.
"What we are trying to do here is to really reshape and redefine electronics ... to look a lot more like the human body, in this case the surface layers of the skin," said John Rogers, a professor in the materials science and engineering department at the University of Illinois at Urbana-Champaign.
"The goal is really to blur the distinction between electronics and biological tissue."
To develop the new monitoring device, researchers created a new class of microelectronics technology they call an epidermal electronic system (EES), which incorporates miniature sensors, light-emitting diodes, tiny transmitters and receivers, and networks of carefully crafted wire filaments.
"Our goal was to develop an electronic technology that could integrate with the skin in a way that is mechanically and physiologically invisible to the user," said Rogers.
"We found a solution that involves devices we designed to achieve physical properties that match to the epidermis itself. It's a technology that blurs the distinction between electronics and biology."
The scientists used a combination of careful theoretical modeling and precise micro-manufacturing to develop a new type of ultra-thin, self-adhesive electronics device that effectively measures data about the heart, brain waves and muscle activity "“ all without the use of bulky equipment, conductive fluids, or glues.
Although existing technologies accurately measure heart rate, brain waves and muscle activity, EES devices offer the opportunity to seamlessly apply sensors that have almost no weight, no external wires and require negligible power.
Furthermore, because of the small power requirements, the devices can draw power from stray (or transmitted) electromagnetic radiation through the process of induction, and can even harvest a portion of their energy requirements from miniature solar collectors.
The EES designs produce flat devices less than 50-microns in diameter -- thinner than a human hair -- that can be integrated onto the polyester backing familiar from stick-on tattoos.
The devices are so thin that close-contact forces known as van der Waals interactions dominate the adhesion at the molecular level, so the electronic tattoos adhere to the skin without any glues and stay in place for hours.
The study demonstrated device lifetimes of up to 24 hours under ideal conditions.
"The mechanics behind the design for our serpentine-shaped electronics makes the device as soft as the human skin," said engineer Yonggang Huang of Northwestern University, one of the project's lead researchers.
"The design enables brittle, inorganic semiconductors to achieve extremely vast stretchability and flexibility. Plus, the serpentine design is very useful for self adhesion to any surface without using glues."
While some areas of the body, such as the elbow, are ill suited to adhesive electronics, most regions commonly targeted for medical and experimental studies are ideal, including the forehead, extremities and the chest.
This means that regions of the body that were previously difficult to fit with sensors may now be monitored, including the throat.
"This type of device might provide utility for those who suffer from certain diseases of the larynx," said Rogers.
"It could also form the basis of a sub-vocal communication capability, suitable for covert or other uses."
"This work is really just beginning," said Rogers.
"On the technology side, our focus is on wireless communication and improved solutions for power"”such as batteries, storage capacitors and mechanical energy harvesters"”to complement the inductive and solar concepts that we demonstrate in the present paper."
The researchers are also exploring clinical approaches, particularly for ailments where sensor size is vital, such as sleep apnea and neonatal care.
Longer term, they hope to incorporate microfluidic devices into their technology, opening up a new arena of electronic bandages and enhanced-functioning skin, potentially accelerating wound healing or treating burns and other skin conditions.
A report about the EES technology is published in the August 12, 2011, issue of the journal Science.
Image 1: The newly developed device, an epidermal electronic system created by an international team of engineers and scientists. Credit: J. Rogers, University of Illinois
Image 2: A newly developed stick-on tattoo with integrated sensor technology, prior to application (from reverse). Credit: J. Rogers, University of Illinois
Image 3: When compressed and pulled, the epidermal electronics device conforms with the skin, remaining in place and intact. Credit: J. Rogers, University of Illinois
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