Engineers make electronic sensors 'so light and thin users forget they have them on'

With cheaper sensors, the onward march of the Internet of Things (IoT) and a desire to use technology to better understand our everyday lives, more people are using wearables than ever before.

However, despite big advances in collecting and processing data, the materials used in wearable electronics have not changed much.

Now, a team of researchers say they have made an electronic sensor “so light and thin that users forget they even have it on”. The elastic electrode could help develop non-invasive devices for continuously monitoring people’s health over a long period, the University of Tokyo team said.

Wearables monitoring heart rate and other vital signs have become more popular in recent years. Some use lightweight, highly elastic materials attached directly onto the skin for sensitive measurements, but the ultrathin films and rubber sheets are deemed unsafe for long-term use because of a lack of breathability. The materials prevent sweating and block airflow around the skin, causing irritation and inflammation, which could cause lasting damage.

A group led by professor Takao Someya at the Tokyo Graduate School of Engineering developed its new hypoallergenic sensor after hearing that devices are needed for continuous monitoring of more than a week in medical and sports applications. The device is made of “breathable nanoscale meshes” of polyvinyl alcohol (PVA) and gold, materials considered safe and biologically compatible with the body. It is applied by spraying a small amount of water on it, which dissolves the PVA nanofibers and allows it to stick to bumpy surfaces on human skin such as sweat pores or the ridges of a fingerprint pattern.

The team tested the sensors on 20 people and found no inflammation after a week of use. They also found the porous mesh structures are more permeable than other materials and are very durable, surviving more than 10,000 repeated bends and stretches. The sensors could monitor patients’ vital signs with no stress or discomfort, the team said.

The wearable technology sector is growing rapidly, said Helen Meese, head of healthcare at IMechE. “Wearables will play a significant role in the home, giving patients greater flexibility to monitor and control their treatment.  These devices will also enable clinicians to monitor patients remotely, allowing them to detect the onset of illness before it happens. This will prevent distress to the patient and reduce long stays in hospital.”

Devices to monitor diabetes, heart and lung disease and even dementia are being developed and trialled, she said to Professional Engineering. Comfort is key for any wearable device, she added.

“Anyone who has had to wear a heart monitor either in the gym or for medical purposes, knows how uncomfortable the straps can be over time,” she said. “If the wearable technology is uncomfortable patients will stop using it, which could in the long term be detrimental to their health.” More devices will be built into clothes in future, she added.

The research was published in Nature Nanotechnology.