3,600 crystals in wearable  skin   monitor health 24/7 A new wearable medical device that uses up to 3600 liquid crystals can quickly let you know if you  re having heart trouble or if it  s simply time to slather on some moisturizer.The small device approximately five centimeters square can be placed directly on the skin 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 color the wearer knows something is awry. Our device is mechanically invisible it is ultrathin and comfortable much like skin itself says Yonggang Huang professor of civil and environmental engineering and mechanical engineering at Northwestern University.Huang and colleagues 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 Huang says.  This is the first device of its kind. The technology and its relevance to basic medicine have been demonstrated in the study but additional testing is needed before it can be put to use. Details are reported online in the journal Nature Communications. The device is very practical says Yihui Zhang co-first author and research assistant professor of civil and environmental engineering.  When your skin is stretched compressed or twisted the device stretches compresses or twists right along with it. 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 3600 liquid crystals each half a millimeter square laid out on a thin soft and stretchable substrate.When a crystal senses temperature it changes color 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 says John A. Rogers the paper  s corresponding author 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 3600 liquid crystals the photonic device has 3600 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.