Japanese Researchers Print Sweat-Powered Cells for Wearable Sensors Without Batteries

A Printable Patch That Turns Sweat Into Power

Researchers at Tokyo University of Science in Japan have developed a water-based enzyme ink for printing thin biofuel cells on paper, opening a route toward wearable sensors that draw electricity from sweat instead of rechargeable batteries. Their research, published online on February 6, 2026, in ACS Applied Engineering Materials, reports a peak power density of approximately 165 microwatts per square centimeter, or around 1,065 microwatts per square inch, at 0.63 volts.

Associate Professor Isao Shitanda, from the university's Department of Pure and Applied Chemistry, led the team. Its central advance concerns how the cells are made: the ink allows the active components to be screen printed in a single step, replacing a sequence of separate applications that can leave uneven layers and inconsistent performance.

The thin patch uses lactate, a compound present in sweat, as fuel. Enzymes help convert chemical energy into an electrical current that can support sensors requiring little power and wireless data transmission. Earlier work by the same research group has demonstrated that this kind of power output can operate Bluetooth Low Energy systems, transmitting sweat lactate readings without battery assistance.

For someone whose fitness tracker stops working at the beginning of a workout, the attraction is straightforward. A sensor powered by sweat could remove the need to find a charging cable or replace a small battery. For manufacturers, the bigger opportunity is a production method that could make such devices practical to build in large numbers.

As of March 26, 2026, the technology remains a research development, with practical implementation anticipated around 2030 after further optimization, testing over long periods and integration with wearable platforms. The work shifts the energy source from electricity stored in a battery to energy harvested from the body's own chemistry.

How Lactate Becomes an Electrical Current

Enzymatic biofuel cells, or EBFCs, use biological enzymes to drive chemical reactions in body fluids. Enzymes are the active ingredients that help those reactions take place. In this design, the main fuel is lactate, a metabolic byproduct that appears in sweat.

Muscles produce lactate as they use glucose for energy during exercise, and some of that lactate leaves the body through perspiration. The system is designed to measure concentrations of roughly 1 to 25 millimolar, equivalent to 1 to 25 millimoles per liter. That range corresponds to the sweat chemistry observed in healthy people during exercise, from light activity to intense exertion.

At one electrode, enzymes help remove electrons from lactate molecules. The electrons travel through an external circuit, producing electrical current. At the other electrode, oxygen from the surrounding air accepts the electrons and completes the reaction. The two electrodes work together to turn the chemical reaction into usable power.

The cell therefore generates electricity while fuel is available, rather than drawing on a stored battery charge. Walking, exercise and routine activities can supply sweat that supports this process. The intended result is passive power generation alongside monitoring, without an external power source.

Bluetooth Low Energy provides a way to send the readings wirelessly while keeping electricity demand low. Earlier demonstrations by the team established a monitoring loop in which sweat supplies fuel and the resulting electricity supports transmission of information about that sweat. During physical exertion, greater sweat production can make more fuel available when monitoring is especially useful.

Why Manufacturing Has Held These Cells Back

Conventional biofuel cell fabrication involves several separate operations. A manufacturer first prints a carbon electrode layer, then applies enzyme and mediator solutions by dripping them onto its surface, a method called drop casting. The deposited liquid must then dry.

Small differences in the amount of liquid applied or the way it dries can change the final device. Uneven enzyme distribution affects both electricity generation and sensing, making it difficult to produce patches with consistent behavior. Those variations complicate quality control and have helped keep promising laboratory devices from widespread use.

Shitanda's team, including Ms. Mahiro Omori of Tokyo University of Science and Mr. Mitsuru Hanasaki of RESONAC Co. Ltd, developed an ink that mixes the active chemistry into the printable material before it reaches the paper. Both electrodes can then be formed in one pass through a mesh screen, replacing the separate application steps.

Shitanda, the associate professor leading the research, described the manufacturing problem and the team's objective:

In order to avoid labor-intensive, inefficient, and expensive EBFC fabrication techniques, we need to bring an enzyme ink to the market that can be printed uniformly and is suitable for mass production.

Screen printing is already widely used in industrial manufacturing, giving the approach a possible route into existing production lines. The formulation also uses water rather than organic solvents that could damage delicate enzyme structures. Keeping the enzymes active after printing is essential because they drive the reactions that produce electricity.

The production advance addresses consistency as well as speed. Combining the ingredients in one printable layer reduces the opportunities for variation between devices. The next task is to turn those laboratory prints into durable sensors that factories can manufacture and people can wear.

The Ingredients That Make the Ink Work

The ink combines magnesium oxide-templated mesoporous carbon with chemical mediators, a binder and a thickener. The carbon is a porous material with a very large internal surface area. Its pores provide space for the active ingredients, while the mediators help transfer electrons during the electrical reactions.

POLYSOL, a water-based polymer emulsion used as the binder, attaches strongly to carbon surfaces while maintaining a stable environment for enzymes within the porous structure. Carboxymethyl cellulose, or CMC, thickens the mixture to give it the consistency needed for screen printing.

Related research published in Nature has shown that CMC helps mesoporous carbon spread more evenly through an ink and improves access to its internal pores. Earlier studies using similar carbon formulations found that adding CMC more than doubled the maximum current density and increased power density by more than 2.5 times compared with electrodes made without it.

Current density describes how much electrical current an electrode produces for a given area. Power density describes the usable electrical power delivered for that area. Improving either measure matters when a device must remain thin and small enough to sit comfortably on skin.

The cathode, the electrode that uses oxygen to complete the circuit, has been particularly difficult to manufacture. Its enzymes are sensitive and hard to stabilize with conventional methods. The researchers embedded the enzyme bilirubin oxidase directly in the printable ink mixture, producing a stable cathode with strong performance in one pass.

The work describes the first successful screen printing of a fully functional cathode using enzyme ink. Making this oxygen electrode printable removes a major remaining bottleneck in scaling up production of the complete biofuel cell.

What the Power and Stability Tests Showed

The complete cell, using lactate and oxygen, reached a maximum power density of 165 microwatts per square centimeter at 0.63 volts. A previously reported value for similar systems was 96 microwatts per square centimeter. The new figure is 69 microwatts per square centimeter higher, an increase of approximately 72 percent using those two values.

The printed electrodes also performed better than conventional drop-cast alternatives in electrochemical testing. In those alternatives, uneven enzyme distribution and poor attachment to the substrate can cause activity to fall to less than half its initial level within minutes to hours. The enzyme ink electrodes showed minimal decline during extended testing.

Stable output matters because a wearable sensor needs to keep operating throughout the period it is being used. A patch that produces enough power at the start but quickly loses activity would be less useful for following a workout or collecting information during care.

The system's operation across lactate concentrations of approximately 1 to 25 millimoles per liter connects the laboratory results to the chemistry of exercise sweat. Its electricity output can support biosensors requiring little energy, while earlier work by the group demonstrated wireless transmission using Bluetooth Low Energy.

The intended application is a thin sensor patch for particular monitoring tasks. Durability during wear, performance over longer periods and integration with the rest of a wearable device still require further work.

From Printed Paper to Factory Production

The team demonstrated a continuous printing process using approximately 400 meters of substrate, equivalent to about 1,312 feet. This roll-to-roll demonstration showed that the manufacturing approach can operate over a long moving length of material, a necessary step toward producing many devices.

Printing at that scale addresses a different problem from generating electricity in a single laboratory sample. A useful commercial process must repeatedly produce working electrodes while preserving the enzymes and keeping device performance consistent.

Storage tests found that keeping the cells at 5 degrees Celsius under vacuum best preserved enzyme activity. That result points toward possible shipping and storage arrangements, although storage stability remains an area for optimization before commercial use.

The paper substrate must also withstand sweat, bending and everyday movement. Temperature changes, exposure to oxygen and other conditions during wear can gradually reduce enzyme effectiveness. Printing a large quantity of material is one milestone; maintaining dependable performance on a moving body is another.

The development and remaining work can be placed on a short timeline:

• February 6, 2026: The research was published online in ACS Applied Engineering Materials.
• March 26, 2026: The technology remained under development, with further durability testing, validation over long periods and wearable integration needed.
• Around 2030: The researchers anticipated possible practical implementation following further optimization and validation.

What Sweat Monitoring Could Offer Athletes

Athletes could use continuous lactate readings to follow changes in exercise intensity and muscle fatigue without stopping for blood draws. Coaches could track fatigue thresholds, while athletes could adjust pacing and training loads using biochemical information rather than estimates alone.

Sweat lactate and blood lactate have a complex relationship. The proposed sports application draws on the connection between sweat chemistry and exertion, using that information to support decisions during training. The research describes that relationship as useful enough to provide actionable insights for performance monitoring.

The power source fits this use particularly well because exercise provides the sweat that carries the fuel. As exertion and perspiration increase, the patch can gain access to more lactate while gathering information about the wearer's physical condition.

Removing a battery would also remove a practical interruption. Charging schedules, missing cables and depleted devices can leave gaps in monitoring. A patch powered by sweat aims to make data collection less demanding for the person wearing it, although comfort and consistent readings across different people and activity levels remain important development goals.

Potential Uses in Healthcare and Heat Protection

Nursing homes and elderly care facilities are among the settings where passive monitoring could be useful. Some patients cannot communicate symptoms clearly, making continuous information about their condition potentially valuable to care staff.

Dehydration, heat stress and infection at an early stage can alter sweat chemistry in measurable ways. The proposed application is a patch that could flag such changes hours before conventional periodic checks detect them, giving staff an opportunity to intervene earlier and potentially reduce emergency escalations.

Heatstroke prevention is another possible use. Sensors that identify early metabolic warning signs could support monitoring when hot weather makes ordinary activities more dangerous. Recovery after surgery and chronic disease management could also benefit from a device designed to collect information without repeated charging.

These are potential applications requiring further development and clinical validation. For medical use, the patch must provide stable readings that clinicians can interpret across different bodies, activities and care situations. The team's immediate manufacturing achievement provides a basis for that work.

A thin patch attached to skin could make regular monitoring easier for patients who struggle with more demanding devices. The researchers expect printing companies and healthcare device manufacturers to be possible adopters once the remaining technical and practical barriers are resolved.

Battery Savings, Waste and the Price of a Patch

The environmental case begins with the number of small batteries used across wearable devices. Removing a coin-cell battery can reduce a sensor's bulk and cost while avoiding the need to replace or dispose of that battery. Disposable medical patches are a particular target because their batteries add components to items intended for limited use.

The article's electronic waste figures put that opportunity in a wider context: the world generated approximately 68.3 million tons of electronic waste in 2022, and only about 22 percent was documented as properly collected and recycled. Sensors without batteries could reduce demand for miniature batteries and simplify device designs, while patches intended for a single use would still create waste.

The production estimate is approximately 10 yen per device if the entire device can be made through full screen printing. That low projected cost could make disposable patches or deployment in large numbers economically practical. It remains a conditional estimate tied to achieving the complete manufacturing process.

The commercial opportunity sits within a wearable medical device market projected to exceed $195 billion by 2030. Eliminating batteries addresses a persistent engineering problem in that market: how to keep small sensors powered without adding weight, maintenance or repeated interruptions.

Further progress depends on preserving enzyme activity, making the paper structure durable, confirming performance over long periods and connecting the printed cell to useful wearable systems. Comfortable patches, dependable measurements and signals that users and clinicians can understand will determine the value of the finished devices.

The research brings manufacturing closer to the needs of those devices by combining active ingredients in a printable ink and demonstrating continuous production. Its proposed destination is monitoring that works through the simple act of wearing a sensor, supporting exercise, care and a safer, healthier daily life.

The Essentials

• Tokyo University of Science researchers developed a water-based enzyme ink for printing biofuel cells powered by lactate in sweat.
• The research, published online on February 6, 2026, reported approximately 165 microwatts per square centimeter at 0.63 volts.
• Associate Professor Isao Shitanda led the team, which included Mahiro Omori and Mitsuru Hanasaki of RESONAC Co. Ltd.
• The ink allows both electrodes to be printed in one pass on paper, replacing separate application steps that can produce uneven results.
• The system measures lactate concentrations of roughly 1 to 25 millimolar. Earlier work by the group demonstrated transmission using Bluetooth Low Energy without batteries.
• A continuous printing demonstration used approximately 400 meters of substrate. Storage at 5 degrees Celsius under vacuum best preserved enzyme activity.
• Potential applications include sports monitoring, elderly care, heatstroke prevention, recovery after surgery and chronic disease management.
• Full screen printing could bring production costs to approximately 10 yen per device. Practical implementation is anticipated around 2030, following further optimization, durability testing, clinical validation and wearable integration.