'Skin-like' device monitors heart and skin health

A new wearable colour-changing device can quickly alert a person if they are having cardiovascular trouble or if it's simply time to put on some skin moisturiser, according to a new study.
The small device, approximately five centimetres square, can be placed directly on the skin and worn 24/7 for around-the-clock health monitoring.
The wireless technology uses thousands of tiny liquid crystals on a flexible substrate to sense heat. When the device turns colour, the wearer knows something is awry.
"Our device is mechanically invisible - it is ultra-thin and comfortable - much like skin itself," said Northwestern University's Yonggang Huang, one of the senior researchers.

The research team, including investigators at University of Illinois at Urbana-Champaign, 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. This is the first device of its kind," Huang said.

"The device is very practical - when your skin is stretched, compressed or twisted, the device stretches, compresses or twists right along with it," said 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.

The device is an array of up to 3,600 liquid crystals, each half a millimetre square, laid out on a thin, soft and stretchable substrate.
When a crystal senses temperature, it changes colour, Huang said, 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," said John A Rogers, the paper's corresponding author and professor of materials science and engineering at the University of Illinois.

With its 3,600 liquid crystals, the photonic device has 3,600 temperature points, providing sub-millimetre 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, researchers said.
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.
The research was published in the journal Nature Communications.