Skin-like device monitors cardio health

An experimental wearable medical device could alert a person that he is having cardiovascular trouble – or that he simply needs some skin moisturizer, according to a study from Northwestern University and University of Illinois at Urbana-Champaign researchers.

The device, approximately 5cm², is worn directly on the skin for 24/7 health monitoring. This wireless technology uses thousands of tiny liquid crystals on a flexible substrate to sense heat, and when the device turns a color, the wearer knows something is awry.

“Our device is mechanically invisible – it’s ultrathin and comfortable – much like skin itself,” says Northwestern’s Yonggang Huang, who led the portion of the research focused on theory, design, and modeling. The research team tested the device on people’s wrists.

“One can imagine cosmetics companies being interested in the ability to measure skin’s dryness in a portable and non-intrusive way,” explains Huang, the Joseph Cummings Professor of Civil and Environmental Engineering and Mechanical Engineering at Northwestern’s McCormick School of Engineering and Applied Science.

The technology and its relevance to basic medicine were demonstrated in this study, although additional testing is needed before the device can be put to use.

“The device is very practical – when your skin is stretched, compressed, or twisted, the device stretches, compresses, or twists right along with it,” says Yihui Zhang, co-first author of the study and research assistant professor of civil and environmental engineering at Northwestern.

The technology uses the transient temperature change at the skin’s surface to determine blood flow rate, which is of direct relevance to cardiovascular health and skin hydration levels. (When skin is dehydrated, the thermal conductivity property changes.)

The device is an array of up to 3,600 liquid crystals, each 0.5mm2, laid out on a thin, soft, and stretchable substrate.

When a crystal senses temperature, it changes color, Huang says, and the dense array provides a snapshot of how the temperature is distributed across the area of the device. An algorithm translates the temperature data into an accurate health report, all in less than 30 seconds.

“These results provide the first examples of epidermal photonic sensors,” explains John A. Rogers, the paper’s corresponding author and Swanlund Chair and professor of materials science and engineering at the University of Illinois. “This technology significantly expands the range of functionality in skin-mounted devices beyond that possible with electronics alone.”

With its 3,600 liquid crystals, the photonic device has 3,600 temperature points, providing sub-millimeter spatial resolution that is comparable to the infrared technology currently used in hospitals.

The infrared technology, however, is expensive and limited to clinical and laboratory settings, while the new device offers low cost and portability.

The device also has a wireless heating system that can be powered by electromagnetic waves present in the air. The heating system is used to determine the thermal properties of the skin.

Northwestern University
www.northwestern.edu

University of Illinois at Urbana-Champaign
www.illinois.edu

Photo credit: John A. Rogers, University of Illinois