The next step in moving fully integrated textile electronics from the lab to the wardrobe is figuring out how to power wearable gadgets without having to carry a solid battery around in the old-fashioned way. Researchers from Drexel University, the University of Pennsylvania and Accenture Labs in California have taken a new approach to the challenge by building a complete textile energy network that can be charged wirelessly. In their recent study, the team reported that it could power textile devices, including a heating element and environmental sensors that transmit data in real time.

Published in the journal Materials todayThe article describes the process and viability of constructing the grid by printing on non-woven cotton textiles with an ink composed of MXene, a type of nanomaterial. created at Drexelwhich is both highly conductive and durable enough to withstand the folding, stretching and washing that clothing undergoes.

The proof of concept represents a significant development for wearable technology, which currently requires complex wiring and is limited by the use of rigid, bulky batteries that are not fully integrated into clothing.

“These bulky energy supplies typically require rigid components that are not ideal for two main reasons,” said Yuri Gogotsi, PhDdistinguished university and Bach Professor in Drexel’s College of Engineering, who led the research. “First, they are uncomfortable and intrusive for the user and tend to deteriorate at the interface between the hard electronics and the soft textile over time. A particularly difficult problem for electronic textiles to solve is that washability.”

In contrast, the textile grid proposed by the team was printed on a lightweight and flexible cotton substrate the size of a small patch. It includes a printed resonator coil, called an MX coil, which can convert electromagnetic waves into energy, enabling wireless charging; and a series of three textile supercapacitors — previously developed by Drexel and Accenture Labs – which can store energy and use it to power electronic devices.

The network was capable of wireless charging at 3.6 volts – enough to power not only wearable sensors, but also digital circuits in computers or small devices, like wristwatches and calculators. Just 15 minutes of charging produced enough energy to power small devices for over 90 minutes. And its performance hardly diminished after a long series of folding and washing cycles to simulate wear and tear placed on clothing.

In addition to testing the grid with small electronic devices, collaborators at the University of Pennsylvania, led by Flavia Vitale, PhD, associate professor of neurology, demonstrated that it can also power wireless biosensor electrodes based on MXene – called MXtrodes – which can monitor muscle movement.

“Beyond clothing applications requiring energy storage, we have also demonstrated use cases that may not require energy storage,” said Alex Inman, PhD, who helped make this research during his internship at Accenture Labs, while he was a doctoral student and research assistant at Accenture Labs. Gogotsi in the AJ Drexel Nanomaterials Institute. “Situations with relatively sedentary users – an infant in a crib or a patient in a hospital bed – would enable direct-feeding applications, such as continuous wireless monitoring of movement and vital signs.”

With this in mind, they also used the system to power a set of commercially available temperature and humidity sensors and a microcontroller to broadcast the collected data in real time. A 30-minute wireless charge powers the sensors’ real-time broadcasts – a relatively power-hungry feature – for 13 minutes.

Finally, the team used the MX coil to power a textile-printed heating element, called a Joule heater, which produced a temperature gain of around 4 degrees Celsius as a proof of concept.

“There are many different technologies that could be powered by wireless charging. The main thing to consider when choosing an app is that it should make sense for a portable app,” Gogotsi said. “We tend to look at biological sensors as a very interesting application because it’s the future of healthcare. They can be integrated directly into textiles, thereby increasing data quality and fidelity and increasing user comfort. But our research shows that a textile-based power grid could power a large number of devices: fiber-based LEDs for fashion or workplace safety, wearable haptics for AR/VR applications like job training and entertainment, and controlling external electronics where a stand-alone controller may be undesirable.

The next step in the development of this technology is to show how the system could be scaled up without diminishing its performance or limiting its ability to be integrated into textiles. Gogotsi and Inman predict that MXene materials hold the key to translating various technologies into textile form. Not only can MXene ink be applied to most common textile substrates, but a number of MXene-based devices have also been demonstrated as proofs of concept.

“We’re producing enough power from wireless charging to power many different applications, so the next steps come down to integration,” Inman said. “One of the main ways MXene can help you is that it can be used for many of these features (conductive traces, antennas and sensors, for example) and you don’t have to worry about material mismatches that might cause electrical or mechanical failure.