Engineers at Northwestern University, Evanston, IL, and University of Illinois at Urbana-Champaign have teamed up to create a new wearable medical device that can quickly alert a person if they are having cardiovascular trouble or if their skin is simply too dry.

Picture of a device with calibration colors operating on the curved surface of the skin.

The small device, which looks like a patch approximately five centimeters square, can be placed directly on the skin and worn 24/7 for around-the-clock health monitoring. Its wireless technology uses thousands of tiny liquid crystals on a flexible substrate to sense heat and change colors to indicate a particular condition.

The device is an array of up to 3,600 liquid crystals, each half a millimeter square, laid out on a thin, soft and stretchable substrate. It was tested on people’s wrists.

As reported online in the journal, Nature Communications, as the wearer’s skin is stretched, compressed or twisted, the device stretches, compresses, or twists as well. 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.

According to John A. Rogers, Swanlund Chair and professor of materials science and engineering at the University of Illinois, “The devices are very simple, with potential to be very low in cost. Because the readout is colorimetric, the data can be acquired and processed using the digital camera function on a standard cellphone”.

When a crystal senses temperature, it changes color, and the dense array shows how the temperature is distributed across the area of the device. Then, an algorithm translates the temperature data into a health report within 30 seconds.

“The device could be used to measure temperature and skin hydration levels near a wound site, for example”, explained Rogers. “It can be used to monitor transient blood flow dynamics from experiments involving occlusion, for the purpose of assessing cardiovascular health, etc. These results provide the first examples of ‘epidermal’ photonic sensors,” he explained.

With its 3,600 liquid crystals, the device has 3,600 temperature points, providing sub-millimeter spatial resolution that, they say, is comparable to the infrared technology currently used in hospitals, but at a much less expensive cost, and greater portability.

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