Flexible tattoo sensors measure blood flow under the skin

November 03, 2015 // By Paul Buckley
An international team led by researchers at the University of Illinois at Urbana-Champaign have unveiled an experimental sensor that clings to skin like a temporary tattoo and provides 24-hour monitoring of  blood flow wherever a patient goes.

A wearable sensor would provide the equivalent of a round-the-clock video of a person’s blood flow throughout the day. Testing showed that a flexible 'epidermal electronics' blood flow monitor developed by an international team led by researchers at the University of Illinois at Urbana-Champaign can measure the blood flow in the outermost 1 to 2 millimeters of skin - even for human bodies in motion. The development promises the potential to create a future wearable device that could continuously measure the blood flow of patients while they go about their daily lives.

“Say you have diabetic patients and want to be able to monitor changes in specific blood vessels continuously for 24 hours a day,” explained Richard Chad Webb, a Ph.D. candidate in materials science and engineering at the University of Illinois. “There’s no way of doing that today.”

The University of Illinois team developed the wearable device in cooperation with the U.S. National Institutes of Health and a broader group of U.S. and Chinese researchers. Webb was the lead author of a paper detailing the group’s work; it was published in the 30 Oct 2015 online issue of the journal Science Advances.

Most state-of-the-art devices for measuring blood flow use optical imaging techniques that require patients to stay still during the process. Webb and his colleagues turned to flexible electronics technology to find a possible wearable solution. (One of the study’s coauthors is John Rogers, a materials scientist and engineer at the University of Illinois whose lab has pioneered many examples of biocompatible flexible electronics.)

Researchers developed a lightweight, ultra-thin device that sits on top of the skin without distorting the blood flow it seeks to measure. The device clings tightly to the skin due to van der Waals forces which are the weak attractive forces between molecules. The attraction prevents any motion between the sensor and skin that could affect the accuracy of readings. As a backup, medical tape can ensure the device stays put.

Image: University of Illinois at Urbana-Champaign

“Fundamentally, what we were trying to do was remove the relative motion between the body and detector system,” said Webb. “That allows you to get to same clinical information [as state-of-the-art optical imaging devices] without the restriction of immobilizing somebody.”