Your Body, the Battery: Powering Gadgets From Human ‘Biofuel’

In order to stay alive, our bodies must burn between 2,000-2,500 calories a day – which is enough energy to power a modestly used smartphone. So if just a fraction of that energy could be siphoned, our bodies could in theory be used to run any number of electronic devices. Researchers are currently working on a new generation of devices that might not just be worn near our bodies, but could be powered by them.

So where would the energy come from?

Our ears
The ears of mammals contain a tiny electric voltage called the endocochlear potential (EP). In 2012, researchers in Massachusetts developed an “energy harvester chip,” about the size of a fingernail, designed to extract electrical energy directly from the EP. Even though the electric power produced by the chip—about a nanowatt (a billionth of a watt)—is still about a million times too low to power an electronic implant, it’s a nanowatt more than had been generated before, making this an important proof-of-concept. If the power output of future prototypes can be boosted, the natural voltage of the inner ear could someday be used to power hearing aids; it could even allow the development of implants to treat diseases which originate there, such as Ménière’s disease.

Feet and heat
Anyone who’s used a bicycle generator or wind-up flashlight understands the idea of converting kinetic energy into electricity—but things have gotten a tad more complex.

In the past few years, researchers have started to exploit a unique property of some materials, known as piezoelectricity, to generate electricity from human movement. In 2013, a Chinese-US research team invented an elastomer-based piezoelectric fabric able to generate electricity using only the kinetic energy of human locomotion. When a piece of this fabric was worn as a shoe insole by a volunteer, walking generated enough electricity to illuminate 30 LEDs. What’s more, when the same fabric was applied onto a shirt that was then artificially moved, it charged a lithium-ion battery in a matter of hours.

Additionally, piezoelectricity is being used to harvest energy from internal organs. Last year, US-based researchers successfully generated electricity from the beating hearts, lungs, and diaphragms of (sedated) cows and sheep, all by attaching an ultra-thin piezoelectric material to the organs. Impressively, the implanted fabric generated about a microwatt of power (one millionth of a watt)—roughly the amount needed to run a cardiac pacemaker.

Blood
Probably the single biggest step toward harnessing the power of our bodies has been the development, in the last few decades, of enzymatic biofuel cells (EFCs)—small, battery-like devices which can generate electricity by breaking down the energy-rich chemicals in bodily fluids. And when it comes to energy-rich bodily fluids, blood is hard to beat.

In 2010, French developers implanted an inch-long EFC device into the abdomen of a live rat, where it operated successfully for 11 days—apparently without much discomfort on the part of the host. During this time, it continually generated around two microwatts of power, which is more than enough to power a pacemaker in theory. And in 2012, another French team (including researchers from the 2010 effort) constructed an improved, carbon nanotube-based EFC, which when implanted into a rat’s abdomen, generated around 40 microwatts of power, which the team actually used to operate both an LED and a digital thermometer.

Sweat
Human sweat is rich in a compound called lactate, which can also be used to generate electricity using EFCs. In 2014, a group of scientists at UC San Diego came up with a wearable, textile-based EFC that could be integrated into sweat bands. A volunteer wore one of these while riding an exercise bike and the cyclist’s sweat allowed the fuel cells to generate electricity. The sweat produced enough power to run an electronic device—either an LED or a digital watch—for a few tens of seconds at a time.

It’ll probably be some time before sweat-powered EFCs can run anything like a smart watch, but they’ve progressed rapidly in recent years. There’s every reason to think that one of our less popular bodily fluids could soon be put to good use.

And tears
Whatever our emotional state, we’re always a little dewy-eyed. The cornea is continually kept moist by a film of what are called “basal” tears. These mostly serve to lubricate and nourish the eye, but they’re also full of energy. Among other chemicals, basal tears contain glucose, lactate, and ascorbate (a compound similar to vitamin C), any of which are an excellent fuel source for EFCs.

Last year, bioengineers at the University of Utah, Salt Lake City, developed the first-ever contact lens with an integrated EFC, allowing it to generate electricity from human tears alone. Their prototype consists of an elastomer lens with two thin carbon fiber electrodes wrapped around its perimeter, leaving the center of the lens unobscured. It has not yet been tested in humans, but when the researchers bathed the lens in a synthetic tear solution, it maintained a power output of over one microwatt for three hours. They are planning to test the lens in rabbits later this year.

Biologically powered fuel cells are still a nascent technology, so it may be some time before our bodies are able to power gadgets, regulate hearts, or help us hear. But there’s a good chance you’ll be around when they can do those things—and perhaps even more things.

Curated Article and Photo Credit from Ars Technica