Flexible wearables enabled by graphene

Researchers from the European Commission’s Graphene Flagship have developed a new class of flexible and transparent wearable devices that are conformable to the skin, providing continuous and accurate measurements of multiple human vital signs. Described in the journal Science Advances, these devices can measure heart rate, respiration rate and blood pulse oxygenation, as well as exposure to UV radiation from the sun.

New technological devices enable non-invasive tracking of vital signs beyond fitness monitoring, with wearable technologies also helping prevent common health problems such as heart failure, hypertension and stress-related complications. But current wearable technologies, based on hard components, do not deliver the desired accuracy and can only monitor a limited number of vital signs. To tackle this problem, Graphene Flagship researchers at ICFO – The Institute of Photonic Sciences have created flexible non-invasive optical-based sensors that can measure a broader set of vital signs.

The first of the devices, a flexible and transparent bracelet, adapts to the skin surface and provides continuous measurement during activity. It also incorporates a flexible light sensor that can optically record the change in volume of blood vessels, due to the cardiac cycle, and then extract different vital signs such as heart rate, respiration rate and blood pulse oxygenation. The readout is visualised and stored on a mobile phone interface connected to the wearable via Bluetooth.

The researchers also integrated a graphene health patch onto a mobile phone screen, which instantly measures and displays vital signs in real time when a user places their finger on the screen. The device uses ambient light to operate, promoting low power consumption and allowing continuous monitoring of health markers over long periods of time. This light-sensing technology incorporates graphene and light-absorbing quantum dots, bringing a new form factor and design freedom to the wearable field.

Using the same core technology, the researchers fabricated a flexible UV patch prototype capable of wirelessly transferring both power and data, which operates battery-free to sense the environmental UV-index. The patch operates with low power consumption and has a highly efficient UV detection system that can be attached to clothing or skin, and used for monitoring radiation intake from the sun, alerting the wearer of any possible overexposure.

“This combination of graphene quantum dot-based detectors integrated into flexible bracelets and skin patches enables the exploitation of these graphene-based optical sensors for several wearable applications, from alerting UV exposure to monitoring of vital signs,” said Maria Smolander, the Graphene Flagship Work Package Leader for Flexible Electronics. “Scalability of the fabrication process based on hybrid integration, wireless powering of the device and the possibility to integrate the functionalities into flexible, even stretchable devices are key benefits in this promising development.”

“We are excited about the prospects for this technology, pointing to a scalable route for the integration of graphene quantum dots into fully flexible wearable circuits to enhance form, feel, durability and performance,” added lead author Frank Koppens, Graphene Flagship Work Package Leader for Photonics and Optoelectronics. “These results show that this flexible wearable platform is compatible with scalable fabrication processes, proving that mass production of low-cost devices is within reach in the near future.”

Image caption: This flexible and transparent bracelet uses graphene to measure heart rate, respiration rate and blood pulse oxygenation continuously. Image credit: ICFO.

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