A wearable sensor, just like a tattoo

Temporary tattoos aren’t just for style anymore. Scientists have developed a new wearable sensor that looks and feels like a henna tattoo but can monitor electrical muscle activity and body temperature, too.

In a paper published Monday in Nature Nanotechnology, researchers described a new ultrathin, lightweight, breathable sensor constructed from nanoscale mesh, a spaghetti-like entanglement of fibers a thousand times thinner than a human hair. It can monitor vital signals over a long period of time without inflaming or irritating skin, a side effect of many current devices.

“We succeeded in completely removing the discomfort of wear,” said Takao Someya, a co-author of the paper and professor in the University of Tokyo’s Department of Electrical Engineering and Information Systems. “People cannot even feel the existence of our devices on their skin.”

Existing wearable electronics are often made from a form of polyester or rubber sheets, which get good readings, but don’t allow enough air to pass through. They prevent sweating and often cause itchiness, redness or other irritation, making them unsuitable for long-term use.

Researchers say the new nanomesh device can theoretically be worn for a week or longer without such problems. The drawback is that it can be rubbed off with water, so in reality, it will need to be replaced after every shower or bath.

There is a trade-off between how comfortable the device is and its durability, Someya said, adding that this is an area of future research.

The device is made from nanoscale meshes containing a water-soluble polymer called polyvinyl alcohol and a layer of gold. It can be applied similarly to children’s temporary tattoos. Just spritz water on it, dissolving nanofibers in the patch, and stick it to the skin. The device conforms to the varied textures of human skin, including sweat pores and fingerprint ridges, while still letting air in through tiny gaps.

The researchers used gold in the device for its durability and softness, Someya said, but it could be replaced with aluminum to be more cost effective.

In a test to see how much water vapour could pass through the material, the nanomesh proved more permeable than thin plastic foil or rubber sheet, the study shows. Twenty participants wore a patch of the nanomesh on their forearms for seven days and reported no inflammation.

The sensor can detect touch, temperature and pressure, and read the electrical activity of muscles just as reliably as conventional gel electrodes, the study says. The researchers hope the sensor will make it possible to monitor a patient’s vital signs without discomfort, and athlete’s physiological signals without impeding performance.

“We can see numerous potential applications in the medical field, also in sports and in people’s welfare everywhere,” Someya said.

But the sensor cannot accomplish these tasks alone. “It’s not a full integrated electronic system,” said John A Rogers, a professor of materials science and engineering at Northwestern University, who was not involved in the study. It needs to be combined with a power source and devices to read and transfer the data. “It’s a component of a broader system that could have utility.”

The real benefit of this new sensor is its nanoscale and flexibility, which provides a more intimate skin interface, Rogers added. “What exists today is basically rigid blocks of electronics strapped to the wrist,” he said. “You can’t measure blood flow or blood pressure with that.”

In the future, this new sensor could be used to monitor vital signals of pregnant women or patients undergoing physical rehabilitation at home, he said, or even capture muscle signals that can be used to control prosthetics.

© 2017 The New York Times