Stick-on tattoo replaces wires and cables in patient monitoring

Stick-on tattoo replaces wires and cables in patient monitoring

An ultra-thin, stick-on tattoo that incorporates the latest in sensor technology could one day replace the mass of wires and cables that connect patients to machines to monitor heart rate and brain waves. The new "electronic skin" technology, called epidermal electronics system (EES), was developed by an international team of scientists and engineers who write about their work in the 12 August issue of Science.

The EES is the result of collaboration between the University of Illinois at Urbana-Champaign, Northwestern University, and Tufts University, all in the US, and the Institute of High Performance Computing in Singapore, and the Dalian University of Technology in China.

Corresponding author of the study, John Rogers, a professor in the Materials Science and Engineering Department at the University of Illinois at Urbana-Champaign, describes EES as a "a technology that blurs the distinction between electronics and biology".

"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," he told the press, adding that the physical properties of the electronic skin match those of human skin.

In an accompanying Perspective article in the same issue of Science, Zhenqiang (Jack) Ma, a professor in the Department of Electrical and Computer Engineering at the University of Wisconsin, Madison, writes that the "eletronic skin" that Rogers and colleagues have developed will not only allow patient monitoring to be "simpler, more reliable, and uninterrupted", but will also solve many problems with current systems whose complicated wiring and cables are inconvenient and distressing for patients and their doctors.

Existing technology is already sophisticated and able to monitor a range of physiological variables, such as heart rate, brain wave and muscle activity, but the EES offers a way to do this that is more accessible and convenient, requiring negligible power, and using sensors that are nearly weightless.

The EES devices contain tiny transmitters and receivers, miniature sensors, light-emitting diodes, and networks of carefully crafted wire filaments.

The prototypes look like flat, stick-on, delicate lacework tattoos of modern art done in metallic thread, and are about the size of a postage stamp. In fact the electronic tattoo is integrated onto the polyester backing of stick-on tattoos.

Because they are so thin (less than 50 microns, thinner than a human hair), they don't need glue to stick to the skin, they use close-contact van der Waals forces that act at the molecular level, enabling them to stay in place for hours.

In their study, the researchers found the devices stayed in place for up to 24 hours, under ideal conditions.

Also, because they need very little power, the EES devices can take their power either from stray, or transmitted, electromagnetic radiation (via induction), and also partly from miniature solar panels.

The electronic inorganic components in the devices are normally quite hard and brittle, but for the EES the engineers designed them to have snake-like mechanical properties that allow them to flex and stretch without breaking.

Co-lead researcher Yonggang Huang, Joseph Cummings Professor of Civil and Environmental Engineering and Mechanical Engineering at Northwestern University, said:

"The mechanics behind the design for our serpentine-shaped electronics makes the device as soft as the human skin."

"Plus, the serpentine design is very useful for self adhesion to any surface without using glues," he added.

The self-adhesive electronic skin will be more suited to areas of the body that are more commonly used for medical and experimental monitoring such as the forehead, hands, feet and the chest. It won't be suitable for regions like the elbow, said the researchers.

However, it brings an extra advantage in that regions of the body difficult to reach with current sensor technology, such as the throat, are now accessible. In fact, the study in Science describes an application where the researchers studied the device inserted in the throat to monitor muscle activity during speech.

The researchers reported the device was more than 90% accurate in interpreting words and vocabulary, sufficient to control a voice-activated video game, which is how they tested it.

This suggests another potential application for the EES, voice activation, which for instance could help patients with disease of the larynx, and sub-vocal communication, such as where covert operators could speak without making audible sounds.

The technology for EES came out of Rogers' and Huang's joint efforts to develop flexible electronics for cameras and other devices that require components with complex shapes.

Rogers said they have really only just started working on EES, and want to take it much further.

"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," said Rogers.

The team is also thinking about other medical applications that need small sensors, such as monitoring sleep apnea and newborn babies. And later on, they hope to incorporate tiny devices that can manipulate fluids, to use as an electronic bandage or strip of electronic skin that helps wounds, burns and other skin conditions heal more quickly.

Funds from the National Science Foundation, the US Air Force, Department of Energy and Beckman Institute helped pay for the research.

Off the shelf, on the skin: Stick-on electronic patches for health monitoring (Video Medical And Professional 2020).

Section Issues On Medicine: Medical practice