Wireless health sensors that stick to the skin

Stanford engineers have developed experimental stickers that capture physiological signals from the skin and then transmit these wireless health measurements to a receiver attached to a garment. It's all part of a system called BodyNet.

We tend to take for granted the protective function of our skin, ignoring its other roles in signaling subtleties such as a beating heart or a puff of embarrassment.

Now, Stanford engineers have developed a way to detect physiological signals from the skin through sensors that stick like dressings and transmit wireless readings to a receiver attached to a garment.

To demonstrate this wearable technology, researchers glued sensors to the wrist and abdomen of a test subject to monitor the person's pulse and breathing by detecting stretching and contraction of the skin at each beat. of heart or breathing. Similarly, the elbows and knees stickers of the person followed the movements of the arms and legs by measuring the tightness or the slackening of the skin each time the corresponding muscle flexed.

Zhenan Bao, the professor of chemical engineering whose lab described the system in an August 15 article in Nature Electronics, thinks this portable technology, called BodyNet, will first be used in medical settings such as monitoring patients with sleep disorders or heart conditions. His laboratory is already trying to develop new stickers to detect sweat and other secretions to track variables such as body temperature and stress. Its ultimate goal is to create a range of wireless sensors that stick to the skin and work in conjunction with smart clothing to more accurately track a wider variety of health indicators than smart phones or watches as the consumers are using today.

"We believe that someday, it will be possible to create a network of skin sensors covering the entire body to collect physiological data without disturbing the normal behavior of a person," said Bao, who is also the KK Professor Lee at the School of Engineering.

Expandable, comfortable, functional

Postdoctoral fellows Simiao Niu and Naoji Matsuhisa led the team of 14 people who spent three years designing the sensors. Their goal was to develop a comfortable technology to wear, without batteries or rigid circuits to prevent stickers from stretching and contracting with the skin.

Their eventual design met these parameters with a variant of RFID technology – radio frequency identification – used to control keyless entry in locked rooms. When a person holds an ID card up to an RFID receiver, an ID card antenna retrieves a minuscule amount of RFID energy from the receiver and the receiver. uses to generate a code that it then returns to the receiver.

The BodyNet sticker is similar to the ID card: it has an antenna that recovers some incoming RFID energy from a receiver on the garment to power its sensors. He then takes skin readings and sends them back to the nearest receiver.

But to operate the wireless sticker, the researchers had to create an antenna that could stretch and curl like a skin. They did it by silkscreening in metallic ink on a rubber sticker. However, each time the antenna was bent or stretched, these movements made its signal too weak and unstable to be useful.

To solve this problem, Stanford researchers have developed a new type of RFID system capable of delivering powerful and accurate signals to the receiver despite constant fluctuations. The battery powered receiver then uses Bluetooth to periodically download the sticker data to a smartphone, computer, or other permanent storage system.

The initial version of the stickers was based on tiny motion sensors to take breathing and pulse readings. Researchers are currently studying how to incorporate sweat, temperature and other sensors into their antenna systems.

To move their technology beyond clinical applications and into user-friendly devices, researchers must overcome another challenge: keep the sensor and the receiver close to each other. In their experiments, the researchers hung a receiver on a garment just above each sensor. Individual pairings of sensors and receivers would be suitable for medical monitoring, but to create a BodyNet that can be worn during exercise, antennas should be integrated into clothing to receive and transmit signals, regardless of the type of device. where a sensor is stuck. .