Stretchable Electronics Used in Soft Wireless, Wearable Health Monitor

A wireless, wearable monitor designed with stretchable electronics could enable comfortable, long-term health monitoring of adults, small children, and babies without concern for allergic reactions or skin injury caused by standard adhesive sensors with conductive gels.

The soft and conformable monitor can display electrocardiogram (ECG), respiratory rate, heart rate, and motion activity data as much as 15 m to a portable recording device such as a tablet computer or smartphone. The electronics are mounted on a stretchable substrate and linked to gold, skin-like electrodes via printed connectors that can stretch with the medical film in which they are fixed.

“This health monitor has a key advantage for young children who are always moving, since the soft conformal device can accommodate that activity with a gentle integration onto the skin,” said Woon-Hong Yeo, an assistant professor in the George W. Woodruff School of Mechanical Engineering and Wallace H. Coulter Department of Biomedical Engineering at the Georgia Institute of Technology. “This is designed to meet the electronic health monitoring needs of people whose sensitive skin may be harmed by conventional monitors.”

Details of the monitor were described in the July 24^th issue of the journal Advanced Science. The study was supported by the Imlay Innovation Fund at Children’s Healthcare of Atlanta, NextFlex (Flexible Hybrid Electronics Manufacturing Institute), and by a seed grant from the Institute for Electronics and Nanotechnology at Georgia Tech. The monitor has been tested on animal models as well as humans.

Since the device conforms to the skin, it avoids signal problems that can be generated by the motion of the standard metal-gel electrodes across the skin. The device can even acquire accurate signals from a person who is running, walking, or climbing stairs.

“When you put a conventional electrode on the chest, movement from sitting up or walking creates motion artifacts that are challenging to separate from the signals you want to measure,” he said. “Because our device is soft and conformal, it moves with the skin and provides information that cannot be seen with the motion artifacts of conventional sensors.”

On-going evaluation with a wireless health monitor could enhance the assessment of children and help clinicians identify trends sooner, potentially enabling intervention before a condition spreads, said Dr. Kevin Maher, a pediatric cardiologist at Children’s Healthcare of Atlanta.

The generation of continuous data from the respiratory and cardiovascular systems could allow for the application of advanced diagnostics to detect changes in clinical status, response to therapies and implementation of early intervention. A device to literally follow every breath a child takes could allow for early recognition and intervention prior to a more severe presentation of a disease.

Dr. Kevin Maher, Pediatric Cardiologist, Children’s Healthcare of Atlanta

When used in the home, a wearable monitor might sense variations that might not otherwise be obvious, he said. When the wireless device is used in clinical surroundings, children would not feel “tethered” to equipment. “I see this device as a significant change in pediatric health care and am excited to partner with Georgia Tech on the project,” Maher added.

The monitor uses three gold electrodes fixed in the film that also comprises the electronic processing equipment. The total health monitor measures just three inches in diameter. Soon a more advanced version will measure just half that size. The wireless monitor is currently driven by a small rechargeable battery, but upcoming versions may substitute the battery with an external radio-frequency charging system.

Yeo and his collaborators, including first author and postdoctoral fellow Yun-Soung Kim, are concentrating on pediatric applications due to the need for ambulatory monitoring in children. However, they think that the health monitor could also be used for other patient groups, such as older adults who may also have sensitive skin. For adults, there would be extra benefits.

The monitor could be worn for multiple days, perhaps for as long as two weeks. The membrane is waterproof, so an adult could take a shower while wearing it. After use, the electronic components can be recycled.

Woon-Hong Yeo, Assistant Professor, George W. Woodruff School of Mechanical Engineering and Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology

Two versions of the monitor have been built. One is based on medical tape and engineered for short-term application in a hospital or other care facility, while the other uses a soft elastomer medical film permitted for use in wound care. The latter can stay on the skin for a longer period.

“The devices are completely dry and do not require a gel to pick up signals from the skin,” Yeo explained. “There is nothing between the skin and the ultrathin sensor, so it is comfortable to wear.”

Since the monitor can be worn for extended periods of time, it can offer a long-term record of ECG data useful to understanding potential heart complications.

“We use deep learning to monitor the signals while comparing them to data from a larger group of patients,” Yeo said. “If an abnormality is detected, it can be reported wirelessly through a smartphone or other connected device.”

The monitor’s circuitry is manufactured using thin-film, mesh-like patterns of copper that can flex with the soft substrate. The only part not flexible is the chips, but they are placed on the strain-isolated soft substrate rather than a traditional plastic circuit board.

Going forward, Yeo plans to decrease the size of the device and incorporate features to measure other health-connected factors such as blood oxygen, temperature, and blood pressure. A major breakthrough would be a clinical trial to assess performance against standard health monitors.

For Yeo, who is an expert in nano- and micro-engineering, the probability of seeing the device in clinical trials—and eventually used in children’s hospitals—is a strong incentive.

It will be a dream come true for me to see something we have developed be helpful to someone who is suffering. We all want to see developments in science and engineering translated into improved patient care.

Woon-Hong Yeo, Assistant Professor, George W. Woodruff School of Mechanical Engineering and Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology

Besides those already mentioned, paper co-authors included Robert Herbert, Shinjae Kwon, and Musa Mahmood from Georgia Tech; Yongkuk Lee from Wichita State University; Nam Kyun Kim and Hee Cheol Cho from Emory University; and Donghyun Kim from Yonsei University Wonju College of Medicine in Korea.

This study was aided by a grant from the Imlay Innovation Fund at Children’s Healthcare of Atlanta, NextFlex (Flexible Hybrid Electronics Manufacturing Institute), and the Georgia Tech Institute for Electronics and Nanotechnology, a member of the National Nanotechnology Coordinated Infrastructure, which is supported by the National Science Foundation via award ECCS-1542174.

A wireless, wearable monitor built with stretchable electronics could allow comfortable, long-term health monitoring of adults, babies and small children without concern for skin injury or allergic reactions caused by conventional adhesive sensors with conductive gels. (Video credit: Georgia Tech)