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And now, a sensor for your skin

And now, a sensor for your skin

New Delhi: Microchips and sensors that can be unobtrusively and painlessly worn on the skin are no longer a stretch of the imagination.

A team of American, Chinese and Singaporean scientists have created peelable, extensible, adhesive patches—akin to temporary tattoos—that can host a diverse array of electronics. As of today, these adhesions, the subject of an article in Friday’s edition of Science, have been tested to monitor heart, brain and muscle activity, but they can be modified to work in a range of futuristic applications from electronic bandages to Wi-Fi-receptive ports.

Underlying it all is a technology that allows electronic wires and circuits to be stretched, almost like rubber bands.

“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," says John Rogers, one of the authors and a professor in the materials science and engineering department at the University of Illinois at Urbana-Champaign. “It’s a technology that blurs the distinction between?electronics?and biology."

Rogers and his colleagues from the University of Illinois at Urbana-Champaign, Northwestern University, Tufts University, the Institute of High Performance Computing in Singapore and Dalian University of Technology in China reported their findings in the article.

Roger’s group has previously reported examples of stretchable electronic polymers that can be wrapped around curved surfaces as well as human tissue. Last year, the group developed rubbery heart implants that could be patched onto the muscle’s tissue and monitor its activity. This, however, is the first evidence of materials that don’t need to be implanted and can directly be strapped onto the skin.

Flexible electronics, as this emerging field is called, essentially involves creating extremely thin layers of silicon circuits—which are normally obdurate—that can then be made pliant to a variety of shapes. Better techniques to create such slices have made possible ultra-thin TV displays as well as flexible solar cell arrays.

Other international research groups have developed so-called “electronic skins" that employ organic materials, instead of silicon semiconductors, that are more malleable, but less efficient as processors. However, skin poses multiple levels of engineering challenges with its unique adhesive properties and necessary precautions against toxicity.

G. Ananthakrishna, a senior materials science professor at the Indian Institute of Science, said that the work was significant. “Skin is a highly deformable surface. Being able to design electronics that don’t lose their conductive properties when they are themselves twisted and folded onto skin, is quite remarkable and has several practical applications," he said.

While existing technologies such as electroencephalographs accurately measure a number of physiological activities, epidermal electronic systems, as these devices are called, have almost no weight, no external wires and require negligible power.

Moreover, because of their small power requirements, they can draw power from stray (or transmitted) electromagnetic radiation through the process of induction and also harvest a portion of their energy requirements from miniature solar collectors.

The electronic tattoos are less than 50 microns thick—thinner than a human hair—which are integrated onto polyester-backed surfaces.

Their microscopic breadth means they don’t need glue and are held onto the skin surface by van der Waals forces, which magnify and weld surfaces at the molecular level.

Regions of the body that previously proved difficult to fit with sensors may now be monitored, including the throat, which the researchers studied to observe muscle activity during speech. The recent study demonstrated device lifetimes of up to 24 hours, and didn’t pose skin irritation, according to the authors.

The throat experiment yielded enough precision for the research team to differentiate words in vocabulary and even control a voice-activated video game interface with greater than 90% accuracy.

“This type of device might provide utility for those who suffer from certain diseases of the larynx," Rogers said. “This work is really just beginning. 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."

Monitoring in a natural environment during normal activity is especially beneficial for continuous observation of health and wellness, cognitive state or behavioural patterns.

The researchers used simple adaptations of techniques used in the semiconductor industry, so the patches are easily scalable and manufacturable. Device company mc10 Inc., which Rogers co-founded, is already working on commercializing certain versions of the technology.

Next, the researchers are working to integrate the various devices mounted on the platform so that they work together as a system, rather than individually functioning devices, and to add Wi-Fi capability.

“The vision is to exploit these concepts in systems that have self-contained, integrated functionality, perhaps ultimately working in a therapeutic fashion with closed feedback control based on integrated sensors, in a coordinated manner with the body itself," Rogers said.

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