Wearable tech powered by sweat could eliminate the need for batteries

It sounds bizarre to be true. Your body is active, it generates sweat. Instead of the moisture simply evaporates in the air it acts as a wearable gadget that is placed on the skin. No charging cables, no batteries, no interruptions. This is precisely the concept of a study by The Tokyo University of Science in Japan which is investigating how sweat from humans could be a viable energy source to power wearable technologies.

The team is led by Associate Professor Isao Shitanda and Co-first authors Mahiro Omori as well as Mitsuru Hanasaki, both of RESONAC Team RESONAC created what they call as a water-based enzyme. This breakthrough allows for the development of a small power generator which can be printed directly onto the paper using just one step of manufacturing.

Wearables powered by sweat are important in daily life


Wearable devices for health are becoming more commonplace including fitness trackers and patches to monitor your health. A lot of them analyse sweat as it is a source of important chemical data about the human body. The sweat can show the level of electrolyte, hydration levels as well as the indicators of exertion like lactate.

The issue, however, is always the power. Many wearable sensors depend on tiny batteries that make them bulky and need constant charging. It causes discomfort and limit the lightweight and adaptable these sensors can be. For a long time, researchers have been looking for options that are light as well as safe for contact with skin as well as able of generating the energy needed to run sensors as well as transmit information wirelessly.

This is when the technology powered by sweat starts to become a real possibility. Instead of storing energy, the device produces energy continuously from your body's own energy.

Knowing the scientific basis of the device

In the center of this breakthrough is a device known as an enzyme biofuel cell which is often abbreviated to EBFC. While this may sound complicated, the idea is rather simple. The system uses enzymes that are biological catalysts which cause chemical reactions to allow electrons to be released.

In this instance there is a fuel in the form of lactate, a substance present in sweat, which grows in training. This enzyme removes electrons from lactate on the one electrode. They then move through a circuit, producing an electrical charge. On the other side, oxygen in the air is what completes the process.

It is the result of a tiny but constant flow of electrical energy that is directly generated by sweat.

The challenge in manufacturing was the reason behind this field's slow progress.

While enzymatic biofuels are being studied for a long time however scaling them up to applications in the real world has been a challenge. The traditional method used printing a base coat and the addition of enzyme solutions, drop by drop. This process often results in unbalanced coatings. Thus, two machines made from the same batch can be very different in their performance.

It is crucial to have consistency, particularly when it comes to devices that monitor health. When readings differ between patches and the information becomes unreliable. This is one of most significant obstacles to stop devices powered by sweat from going beyond lab experiments.

The invention of enzyme ink

The latest study addresses this issue by incorporating enzymes directly into the ink to print. The enzyme-based ink is made up of porous carbon, electron transfer mediators and water-based elements that are non-toxic to enzymes.

Since everything is mixed at beginning, the device could be made through screen printing, a proven industrial process. It allows the whole biofuel cells, which include the oxygen electrode that is a challenge, to be printed in one step. It results in an improved uniformity and increased scalability of the manufacturing method.

According to researchers they also recommend roll-to-roll printing, which means that the long sheets produced by these machines could be printed in continuous fashion. They have also printed over some 400m distances which suggests the possibility of massive production that is low cost.

What exactly do performance numbers are?

When tested in laboratory conditions it was able to achieve the current of 0.63 millivolts with a peak performance of 165 microwatts for each square centimeter. Although the numbers might seem to be small, they're important for wearable technology. They provide enough power to low-energy sensors as well as enable brief periods of wireless communications, for example, Bluetooth low Energy signals.

It was also equipped to monitor lactate levels in a range typical of exercise between 1 and 25 millimoles per milliliter. It could also measure physical exertion at a real time pace.

Additionally, the cost for every patch will be around 10 Japanese dollars, which is approximately six cents. This makes the patch economically feasible for mass usage.

From laboratory promises to real-world applications

Despite the positive outcomes, there are still a few hurdles prior to the technology reaching the masses. The patches that wearables are made of must be able to withstand bend the friction and various temperatures of sweat. In real-life, the environment is more messy than laboratory environments controlled in a lab, and ensuring that the patch performs consistently under the conditions that are encountered is vital.

Also, there is the issue about interpretation. Although sweat lactate may provide evidence of exertion, it can take blood samples into consideration. More research is required to link these measurements to relevant fitness or health knowledge.

An important step forward based on previous studies

This research builds upon previous research conducted by the same team. In 2021, they showed an ink-based, lactate-based biofuel array that could generate 3.66 Volts and 4.3 milliwatts. That's sufficient to power a lower-energy Bluetooth device within the controlled environment. The latest enzyme-based ink method is a step towards practical and scalable application.

The future in which your body powers the devices you use

The concept of powering electronic devices by sweat might still seem strange, however it's an evolutionary shift towards the more natural and integrated technology. Instead of having to rely on the external source of power, these devices can draw power directly from your body.

When the other issues are solved, sweat-powered devices can be a aspect of your daily routine. Simple exercise can enhance your well-being but also provide the power needed to track it.