Researchers say new technology could eliminate the need for batteries on fitness devices, allowing them to be lighter and sleeker.

What if you could use the human body to power electronic devices?

A group of scientists at the University of California San Diego (UCSD) are doing just that.

In an article published in the journal Energy & Environmental Science, the authors reported their recent invention of a flexible skin patch that generates electricity from human sweat.

“It’s like a battery, but the power is generated by a chemical called lactate,” Amay Bandodkar, first author of the paper, told Healthline.

Now a postdoctoral fellow at Northwestern University, Bandodkar recently completed a PhD in nanoengineering at UCSD.

“The lactate in sweat is basically consumed by this patch, which generates electricity that can be used for powering other medical devices,” he said.

The patch exhibits an open circuit voltage of 0.5 volts, and a power density of almost 1.2 milliwatts per centimeters squared.

That represents the highest power density recorded to date for a wearable biofuel cell. In fact, it’s nearly 10 times more powerful than past devices.

So far, the developers have used the patch to power a light emitting diode (LED) and a Bluetooth Low Energy (BLE) radio.

In the future, they believe it may be used to power sensors designed to monitor wearers’ health and fitness.

“Right now, we have all these wearable sensors and systems that require bulky batteries. And many times, the weight of the battery is much higher than the weight of the actual device,” Bandodkar explained. “But what you have with this patch is an on-body energy harvesting system, which can generate electricity from your body and use it for powering other wearable systems.”

By eliminating the need for bulky batteries, wearable biofuel cells may help experts develop smaller and lighter medical devices that can be worn on the body, and powered by it, too.

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While more research is needed, this patch represents a significant development in the field of wearable biofuel cells.

In addition to exhibiting high power density, it’s also flexible enough to conform to the human body.

“In order to make a wearable device, we have to make it very flexible or even stretchable,” Yue Gu, a co-author of the paper and second-year PhD student at UCSD, told Healthline.

Otherwise, the device would break under the strain of movement.

To create a flexible device, the researchers arranged rigid 3-D carbon nanotube structures into a stretchable “island-bridge” configuration.

In this design, firmly bonded islands are connected by serpentine bridges.

When they are subjected to movement, the bridges unwind and deform.

This allows the bridges to accommodate stress, while limiting strain on the islands.

“We were able to incorporate a lot of active biofuel cell materials into these 3-D carbon nanotube structures,” Bandodkar explained. “Then we were able to put these rigid structures on top of these isolated islands. So even when we stretched it, none of the stretch was experienced by these structures.”

“This is how we were able to maintain the high-power density, while still having the soft stretchable properties incorporated,” Bandodkar added.

This innovative approach allowed the researchers to create a wearable biofuel cell that can generate stable power for two days, despite repeated stretching.

According to Gu, it’s the first device that integrates a biofuel cell into the island-bridge design.

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To develop a device like this, interdisciplinary teamwork is critical.

Members from three different research groups at UCSD were involved in this project, including groups lead by co-authors Joseph Wang, PhD; Sheng Xu, PhD; and Patrick Mercier, PhD.

“Professor Wang’s group has expertise in making the biofuel cell’s active components,” Bandodkar explained. “Professor Xu’s group has expertise in making these soft, stretchable island-bridge structures. And Professor Mercier’s group has experience in low-energy electronics.”

In the past, researchers from these groups have also worked on other wearable technologies.

For example, Bandodkar, Wang, and colleagues previously developed tattoo-like sensors designed to monitor electrolyte and glucose levels.

They’re now interested in learning if the biofuel cell skin patch can be used to power such sensors.

“When we were working on these kind of things, the battery is always a problem,” Bandodkar said. “Now, what we want to do is use these biofuel cells to power chemical sensors. That is something that we are in the process of exploring.”

Through their interdisciplinary collaboration, the creators of the biofuel cell skin patch are helping to push the field of wearable health sensors and systems forward.