This power source is shockingly eel-like | Science News for Students

This power source is shockingly eel-like

A new kind of squishy-power generator mimics an electric eel’s zap
May 2, 2018 — 6:45 am EST
hydrogel sheets

When pressed together, sheets of gels can produce electricity. This flexible power source was inspired by electric eels.

Thomas Schroeder and Anirvan Guha

This is one in a series presenting news on technology and innovation, made possible with generous support from the Lemelson Foundation.

Electric eels are legendary for their ability to stun prey with a high-voltage jolt. Inspired by the creature, scientists have adapted the eel’s stunning secret to build a squishy, flexible new way to make electricity. Their new artificial electric “organ” could supply power in situations where regular batteries simply wouldn’t work.

With water as its main ingredient, the new artificial organ can work where it’s wet. So such a device might power soft-bodied robots that have been designed to swim or move like real animals. It might even be useful inside the body, such as to run a heart pacemaker. And it generates power through a simple motion: just a squeeze.

electric eel
Electric eels like the one shown here use special cells called electrocytes to generate electric shocks that stun their prey.
Nathan Rupert/Flickr (CC BY-NC-ND 2.0)

A research team based in Switzerland described the new device February 19 at a scientific meeting in San Francisco, Calif.

Electric eels generate their electric charge using specialized cells. Known as electrocytes, those cells take up most of an eel’s 2-meter- (6.6-foot-) long body. Thousands of these cells line up. Together, they look like rows upon rows of stacked hot-dog buns. They are a lot like muscles — but don’t help the animal swim. They direct the movement of charged particles, called ions, to generate electricity.

Tiny tubes connect the cells, like pipes. Most of the time, these channels let positively charged molecules — ions — flow outward from both the front and back of a cell. But when the eel wants to impart an electric shock, its body opens some of the channels and closes others. Like an electric switch, this now lets positively charged ions flow in one side of the channels and out the other.

As they move, these ions build a positive electric charge in some places. This creates a negative charge in other places. That difference in charges sparks a trickle of electricity in each electrocyte. With so many electrocytes, those trickles add up. Together, they can produce a jolt strong enough to stun fish — or fell a horse.

Dot to dot

The new artificial organ uses its own version of electrocytes. It looks nothing like an eel, or a battery. Instead, colored dots cover two sheets of transparent plastic. The whole system resembles a couple of sheets of colorful, fluid-filled bubble wrap.

The color of each dot denotes a different gel. One sheet hosts red and blue dots. Salt water is the main ingredient in the red dots. The blue dots are made from freshwater. A second sheet has green and yellow dots. The green gel contains positively charged particles. The yellow gel has negatively charged ions.

To make electricity, line up one sheet above the other and press.

eel hydrogel
These dots of colored, squishy gels contain water or charged particles. Squeezing the dots so that they come into contact can generate a small — but useful — amount of electricity.
Thomas Schroeder and Anirvan Guha

The red and blue dots on one sheet will nestle between green and yellow ones on the other sheet. Those red and blue dots act like the channels in the electrocytes. They will let charged particles flow between the green and yellow dots.

Just as in an eel, this movement of charge makes a tiny trickle of electricity. And also as in an eel, a lot of dots together can impart a real jolt.

In lab tests, the scientists were able to generate 100 volts. That’s almost as much as a standard U.S. electric wall outlet delivers. The team reported its initial results in Nature last December.

The artificial organ is easy to make. Its charged gels can be printed using a 3-D printer. And as the main ingredient is water, this system is not costly. It’s also fairly rugged. Even after being pressed, squished and stretched, the gels still work. “We don't have to worry about them breaking,” says Thomas Schroeder. He led the study with Anirvan Guha. Both are graduate students in Switzerland at the University of Fribourg. They study biophysics, or how the laws of physics work in living things. Their team is collaborating with a group at the University of Michigan in Ann Arbor.

Hardly a new idea

For hundreds of years, scientists have tried to imitate how electric eels work. In 1800, an Italian physicist named Alessandro Volta invented one of the first batteries. He called it the “electric pile.” And he designed it based on the electric eel.

“There is much folklore about using electric eels to generate ‘free’ electricity,” says David LaVan. He’s a materials scientist at the National Institute of Standards and Technology in Gaithersburg, Md.

LaVan did not work on the new study. But 10 years ago, he led a research project to measure how much electricity an eel produces. Turns out, an eel isn’t very efficient. He and his team found that the eel needs a lot of energy — in the form of food — to create a small jolt. So eel-based cells “are unlikely to replace other renewable energy sources,” such as solar or wind power, he concludes.

But that doesn’t mean they couldn’t be useful. They are appealing, he says, “for applications where you want a small amount of power without metal waste.”

Soft robots, for example, may be able to run on a small amount of power. These devices are being designed to go into harsh environments. They might explore the ocean floor or volcanoes. They might search disaster zones for survivors. In situations such as these, it’s important that the power source won't die if it gets wet or squished. Schroeder also notes that their squishy gel grid approach might be able to generate electricity from other surprising sources, such as contact lenses.

Schroeder says it took the team a lot of trial and error to get the recipe right for its artificial organ. They worked on the project for three or four years. Over that time, they created many different versions. At first, he says, they didn't use gels. They tried using other synthetic materials that resembled the membranes, or surfaces, of electrocytes. But those materials were fragile. They often fell apart during testing.

Gels are simple and durable, his team found. But they produce only small currents — ones too tiny to be useful. The researchers solved this problem by creating a large grid of gel dots. Dividing those dots between two sheets let the gels mimic the eel’s channels and ions.

The researchers are now studying ways to make the organ work even better.


Power Words

(more about Power Words)

application     A particular use or function of something.

biophysics     The study of physical forces as they relate to living things. People who work in this field are known as biophysicists.

cell     The smallest structural and functional unit of an organism. Typically too small to see with the unaided eye, it consists of a watery fluid surrounded by a membrane or wall. Depending on their size, animals are made of anywhere from thousands to trillions of cells. Most organisms, such as yeasts, molds, bacteria and some algae, are composed of only one cell.

current     A fluid — such as of water or air — that moves in a recognizable direction. (in electricity) The flow of electricity or the amount of charge moving through some material over a particular period of time.

eel     A fish with a snake-like body and no scales. Many migrate from freshwater to salt water when it’s time to spawn.

electricity     A flow of charge, usually from the movement of negatively charged particles, called electrons.

electrocyte     A cell that generates electricity in some types of fish, such as electric eels. Each cell produces only a small amount of electricity, so these cells are typically stacked in large groups to allow the animal to deliver a larger jolt.

environment     The sum of all of the things that exist around some organism or the process and the condition those things create. Environment may refer to the weather and ecosystem in which some animal lives, or, perhaps, the temperature and humidity (or even the placement of components in some electronics system or product).

freshwater     A noun or adjective that describes bodies of water with very low concentrations of salt. It’s the type of water used for drinking and making up most inland lakes, ponds, rivers and streams, as well as groundwater.

gel     A gooey or viscous material that can flow like a thick liquid.

graduate student     Someone working toward an advanced degree by taking classes and performing research. This work is done after the student has already graduated from college (usually with a four-year degree).

grid     (in mathematics or mapping) A network of lines that cross each other at regular intervals, forming boxes or rectangles, or an orderly field of dots that mark where each pair of lines intersect, or cross one another.

ion     (adj. ionized) An atom or molecule with an electric charge due to the loss or gain of one or more electrons. An ionized gas, or plasma, is where all of the electrons have been separated from their parent atoms.

materials science    The study of how the atomic and molecular structure of a material is related to its overall properties. Materials scientists can design new materials or analyze existing ones. Their analyses of a material’s overall properties (such as density, strength and melting point) can help engineers and other researchers select materials that are best suited to a new application. A scientist who works in this field is known as a materials scientist.

membrane     A barrier which blocks the passage (or flow through) of some materials depending on their size or other features. Membranes are an integral part of filtration systems. Many serve that same function as the outer covering of cells or organs of a body.

muscle     A type of tissue used to produce movement by contracting its cells, known as muscle fibers.

National Institute of Standards and Technology (NIST)     A U.S. government research agency founded in 1901 as the National Bureau of Standards. Its name changed to NIST in 1988. Over the years, NIST has become a major center for research in the physical sciences. One of its enduring functions is the development of new and more precise ways to measure things, from time and electricity to the size of an atom and wavelengths of light. With facilities in Gaithersburg, Md., and Boulder, Colo., it employs some 3,400 people.

organ     (in biology) Various parts of an organism that perform one or more particular functions. For instance, an ovary is an organ that makes eggs, the brain is an organ that makes sense of nerve signals and a plant’s roots are organs that take in nutrients and moisture.

pacemaker     A small medical device implanted in the body to help control abnormal heart rhythms. This device sends an electrical signal. It stimulates the heart to beat at a regular and healthy rate.

particle     A minute amount of something.

physics     The scientific study of the nature and properties of matter and energy. Classical physics is an explanation of the nature and properties of matter and energy that relies on descriptions such as Newton’s laws of motion. A scientist who works in such areas is known as a physicist.

prey     (n.) Animal species eaten by others. (v.) To attack and eat another species.

renewable energy     Energy from a source that is not depleted by use, such as hydropower (water), wind power or solar power.

robot     A machine that can sense its environment, process information and respond with specific actions. Some robots can act without any human input, while others are guided by a human.

synthetic     An adjective that describes something that did not arise naturally, but was instead created by people. Many synthetic materials have been developed to stand in for natural materials, such as synthetic rubber, synthetic diamond or a synthetic hormone. Some may even have a chemical makeup and structure identical to the original.

transparent     Allowing light to pass through so that objects behind can be distinctly seen.

voltage     A force associated with an electric current that is measured in units known as volts. Power companies use high-voltage to move electric power over long distances.


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Meeting: A. Guha et al. An eel-inspired artificial electric organ: 110 volts from water and salt. Biophysical Society Annual Meeting 2018, Feb. 19, 2018, San Francisco, Calif. Biophysical Journal. Vol. 114, Page 192a, 2018.

Journal: T.H.B. Schroeder et al. An electric-eel-inspired soft power source from stacked hydrogels. Nature. Vol. 552, December 14, 2017, p. 214. doi: 10.1038/nature24670.