The Battery That Never Gets Flat

Humans are complex machines, with moving parts that bend, squish, stretch, flow, quiver, and beat. Scientists are now plugging into these energy sources to solve a common problem afflicting sensors, wearables, and implanted medical devices—the dreaded flat battery.

Devices that are self-powered by design could be the solution, and researchers have discovered that the human body itself can be a handy power source—just in time to power the exploding market in wearables. “Electroceuticals” are starting to challenge pharmaceuticals in medicine, so more people will depend on devices such as implanted electrostimulators and pacemakers in order to stay healthy.

“Biobatteries” and energy scavenging could make these devices energy-autonomous, removing the need for invasive surgery to replace dead batteries. As a bonus, this wireless world would avoid implanted charging cables being dislodged or becoming infected—problems that are all too common today.

Scientists have been working on body-powered devices since the early 2000s—until now, the tech has been too energy-hungry for the minute amounts of electricity that can be harvested from humans. But after two decades of advances, today’s devices consume ultra-low amounts of energy, throwing open the gate to myriad ideas and prototypes that draw power from the people.

A cellular powerhouse

Your cells are basically batteries—biochemical ones that convert sugary fuel into energy. German startup CELTRO is tapping into this living power source by utilizing arrays of microneedles to harvest tiny amounts of energy from hundreds of thousands of cells. CELTRO’s first product will be a tiny autonomous pacemaker. “A muscular contraction, like the heart, starts at one point and then propagates through the whole heart muscle,” says CEO and cofounder Gerd Teepe. “Our idea was to harvest energy at multiple points to use this avalanche effect.” As well as harvesting energy, the multifunctional microneedles will plug into cardiac tissue to monitor the heart and deliver a helping electrical boost to restore pacing, if needed. In 2021, CELTRO raised seed funding for lab-based proof of concept studies.

Paper fuel-cells

French startup BeFC is building biobatteries with green credentials. Its fuel cell uses layers of carbon, cellulose, and glucose—plus a sprinkling of proprietary enzymes. Adding a drop of fluid—say, blood or urine—sets off a reaction that generates electricity. The paper patches could power single-use diagnostic devices and continuous monitoring sensors, such as glucose-monitoring kits for people with diabetes. After use, the cells can even be composted—unlike other miniature batteries that are eventually binned or incinerated. BeFC is currently raising Series A funding and expects to hit the market in 2024 with its first products. 

My quivering heart

Paris-based CAIRDAC is designing a pacemaker that’s powered by the heart itself. Its leadless pacemaker is packed into a capsule containing a piezoelectric energy harvester—a pendulum that swings through heartbeats, blood flow, and vibrations. The oscillations are converted into electricity and stored until the device senses that the heart needs a jolt to reset the rhythm. The startup recently raised €17 million (around $18.3 million) in Series A financing to continue preclinical testing and move toward human trials.

Interior illumination

Solar panels are becoming a common household sight, and they could soon be lighting up med tech, too. Researchers from Monash University in Melbourne, Australia, have found that a solar panel placed under the skin still yields up to 10 percent as much electricity as one in direct sunlight—enough to power an ultra-low consumption sensor. A couple of hours in the sun can run an implantable temperature sensor for 24 hours, and the researchers say the best place for it is between the neck and the shoulder.

The hydroelectric heart

Mini-turbines could harness blood flow and turn it into electricity, according to researchers at the University of Bern in Switzerland. They’ve designed a torpedo-shaped turbine that could be implanted into a blood vessel in the heart, generating electricity from blood flow, much like a hydroelectric power station. A big challenge, as yet unsolved, is how to avoid blood clots forming on the blades of the turbine, but in lab simulations the turbine generated enough energy to power commercially available leadless pacemakers.

Piezo patches

Italian startup PiezoSkin says it has developed an ultra-thin piezoelectric skin patch that can simultaneously measure movements and draw power from them. In one study, it used the patch to monitor neck movements in people with dysphagia, or difficulty swallowing—but the firm’s biocompatible film could also harvest power from other body movements and vibrations for sensors and wearables.

Feeling the heat

Humans radiate around 100 watts a day in thermal energy, and according to Swiss startup Mithras, harnessing this heat could power wearable biosensors and even implanted devices. Its thermoelectric generators, known as TEGs, create electricity by exploiting the temperature difference between the body and the environment. Mithras estimates that with a 5 degree Celsius difference, a 12-square-centimeter TEG skin patch could completely power a cochlear implant. 

This article was originally published in the January/February 2023 issue of WIRED UK magazine.

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