Electric eels and medical implants

This BBC podcast is supported by ads outside the UK. September's always busy. Whole Foods Market can help. Their September stock-up event makes it easy to load your pantry and freezer with flavorful, nourishing food. Even better, there are hundreds of sales. Get dinner going with canned soups and veggies. Lean on frozen pizzas, pastas, and seafood everyone loves. They're built your own family meals feeds for for just $35. Stock up at Whole Foods Market. Get more with BBC Podcasts, wherever you listen. Be the first to listen to your favorite shows, like Evil Genius, Good Bad Billionaire, and Your Dead To Me, with a subscription to BBC Podcasts Premium on Apple Podcasts. You can also enjoy a range of our podcasts, Add Free, with an Amazon Music subscription. There's an ingenious predator lurking in the South American continent. Imagine we're there deep in the Amazonian rainforest. Above us is a vast canopy of overlapping branches and leaves through which the sunlight strains to penetrate with its glistening rays. All around us are the buzzing, chirping, howling sounds of the forest. Let's play the role of a small fish, swimming along a slow-moving stream that feeds into the mighty Amazon River. There's almost no visibility in the murky water, which is clogged with decaying vegetation. But it's okay, because we have the ability to move with speed, weaving our way around objects, our senses are tingling. There's danger nearby, and then suddenly it happens, Zap! Within the blink of an eye, in fact, faster than that. A mere 2,000th of a second, we have been stunned! How muscles twitch and contract uncontrollably. And then suddenly, we're numb, powerless, and unable to escape. But before we've even had a chance to regain our senses, we're in the dark cavern of a very large mouth. We have become prey to an electric eel. For me, the electric eel is one of the most intriguing and powerful predators to inhabit the great river basins of South America. This is an animal with an incredible superpower, the ability to create electricity within its own body, capable of delivering the high-voltage jolt that just immobilized our small fish. The electric eel uses its power to hunt not only for fish, but also amphibians, birds, and even small mammals. This ability to shock also comes in handy as a defense mechanism. Electric eels have even been known to leap out of the water to deliver warning zaps to much bigger land-based predators. In doing this, scientists believe eels are working in a highly sophisticated way. By leaping into the air, the eels are able to deliver a much stronger shock because they lose less power to the surrounding water. This is because water is much better at conducting electricity away from the eel than air. This is easily up there as one of my top 10 animal abilities. What's even cooler about these electromagniacs, if you will, is that electric eels also emit low-voltage electric pulses while swimming, which allows them to communicate with other electric eels and even join together to hunt in a coordinated swarm. The pulses also act as a sort of radar to help navigate and find prey. Seeing as the eel's eyesight isn't that great, it's a pretty useful tool. Perhaps the most important thing you need to know about this amazing creature is that it is in fact not an eel. The electric eel is actually classed as part of the South American Knife Fish family, a relative of the catfish. Although with its slender grey-brown slippery body, long tail and wavy fin that helps propel it through the water, for all intents and purposes, it does look like an eel. Electric eels are big fish that can grow up to two and a half metres in length and can weigh in at more than 20 kilograms. They live mainly on the muddy bottom of slow-moving rivers and streams preferring inconspicuous shaded areas of the forest. But often these waters are choked with decomposing vegetation which strips them of vital oxygen. So, the electric eel has developed a clever adaptation. Although it does have gills, it gets most of its oxygen by breathing at the surface, a bit like the Arapheimer fish, which we also hear about in this season of 30 animals. But unlike the Arapheimer which has developed a modified lung from its swim bladder, the electric eel absorbs oxygen through large blood vessels in its mouth. Although this is one animal that we're quite familiar with, it turns out that we're still learning about these cracking creatures. As recently as 2019, scientists discovered that there are in fact two additional species of electric eel native to South America. Of the three in total, it's one called Electroforest Voltae that has earned itself a top spot in the record books. It has the ability to deliver a devastating electric shock of over 800 volts, the strongest of any known animal. In fact, it's enough to cause an adult human to have a full blown heart attack. Humans have also been known to drown in shallow water after unfortunate encounters with electric eels. But scientists are now putting this deadly power to use for us humans. The electric eel is inspiring the creation of a new type of power source, a soft flesh-like battery that might be used on our bodies and even inside them to power implants. This means they could be used for devices like pacemakers which stimulate the heart and help it to beat regularly and correctly. So, you could say that this powerful zapping predator is being transformed from a heart stopper to a heart saver. Hello, I'm Patrick I and this is Season 2 of 30 Animals that made us smarter, an original podcast from the BBC World Service which explores how animals have helped us solve human problems and inspired some amazing inventions along the way. If you've enjoyed our podcast so far, please spread the word and share it with everyone you know, they will love it. If they've never listened to a podcast before, be a good friend and show them how to find a podcast app and search for this podcast. But don't stop there, while you're at it, show them how to subscribe, it's quick and easy. It also means they'll get all the episodes automatically. Now, if you're feeling generous, please go ahead and leave us a comment on what you think of the show or even perhaps a suggestion for other inspiring animals. The hashtag on social media is 30 Animals. Okay, fun fact time. Did you know the invention of the electric battery was inspired by the electric eel? In the 18th century, electric eels were captured by naturalists and displayed in European theatres. People paid huge amounts to see them and understand how they could generate electricity. One of those fascinated by the eel was the Italian physicist Alessandro Volta, who in 1799, based the design of his electric battery, the world's first, only eels anatomy. In fact, you might recognize his name. The pressure which pushes a current through a circuit, a.k.a. voltage, was named after him. So, how does this electrifying ability work? Well, it all comes down to a particular type of cell within the electric eel's body known as an electrolyte. These cells are thin and disc-like in shape and the electric eel has thousands of them. They're lined up and stacked inside three special organs that can produce both high and low voltage charges. But more about these later. First, let's concentrate on how these special electrocytes cells work. And to make things really simple, let's go back to the basics of how electricity is created. Everything around us, including ourselves, is made up of tiny particles, comprised of of ions, atoms, and molecules. Now, each of these particles can have a positive or negative charge. Electricity is the result of this charge moving from one particle to another. So, back to the electric eel. Once it pinpoints its prey, its brain sends a signal through its nervous system to these special electrolyte cells. These cells are stacked in long rows with fluid-filled spaces between them. To help you picture this, imagine a huge stack of circular pancakes. I'm talking 10, even 20. Each one covered in delicious syrup. Now, turn this stack onto its side so that the pancakes are resting on their edges, and this gives you a good idea of what the electrolyte cells look like along with the fluid inside them. When the eel is at rest, each electrolyte pumps out positively charged particles or ions through the membrane walls on the front and back sides of the cell. When these positive ions meet in the fluid-filled spaces, well, they cancel each other out and nothing happens. But when the eel sends a signal to the electrolyte cells to act, something amazing takes place. The backside of the cell flips direction and lets positively charged particles rush back in. With positive ions now flowing through the cell from back to front, an electrical current is created. Now, back to those three special electricity-producing organs inside the electric eel, the ones that produce those high and low-voltage charges. The located in the tail section, which incredibly makes up a whopping 80% of its body. Inside are thousands of electrolyte cells all lined up such that the ions can flow through them. The effectiveness of this arrangement is enhanced by having multiple rows stacked up on top of one another, which increases the overall voltage that can be delivered at any one time. Think of how sometimes a handheld torch will only turn on when there's lots of batteries lined up inside. It's kind of the same idea. The first of these organs is called the main organ and it's located on the upper side of the eel, stretching from just behind the head to the middle of the tail. Lying directly beneath this but running the full length is the hunter's organ. Between them, they produce the high-voltage pulses that the eel uses to stun its prey and deter predators. These organs are the eel's weapons HQ. From here, they can deliver hundreds of powerful jolts in a single attack. Finally, we have the third organ, which sits just behind the other two and this is known as the sax organ. This produces the lower-voltage pulses, which helps the eel find its prey by creating an electric field around the eel's body, which acts like a bubble of electric current. When another animal enters that space, the eel can sense that its electric field has become distorted. This is a really neat way of helping it to figure out the other animal's position and even what type of animal it might be. All of this in the dark, murky waters. So, how do you get from organs full of electrocytes to soft, fleshy batteries that can work inside our bodies? Well, this is something that's being looked at by a team of scientists at the University of Freeberg in Switzerland. Michael Mayer, Thomas Schroder and Anna Van Guha decided to build their own human-made electric organs stacked full of manufactured electrocytes. However, they quickly discovered this was a bigger challenge than they'd first anticipated. Mainly because the synthetic electrocytes they created were exceptionally delicate. And if one broke, then the entire artificial organ would fail because the current could no longer pass through it. So they decided to simplify the process and did this by using lumps of gel arranged on a sheet. Some of these gels contained highly salted water, whereas others contained water without salt. They were arranged alternatively, in other words, one salt water, one fresh water, another salt water, and another fresh water, and so on. This continued in rows with spaces in between. Left in this state, the gels did nothing. But if they were connected in some way, the different concentrations of salt would mean the particles or ions would now have the ability to flow out of the salt water gel and into the fresh water one. And this, just like the ions flowing in the electric eels' electrocytes cells would create a small electric charge. Okay, we're making progress. But how to connect these lumps? The scientists solve this problem by making another sheet on which they placed more lumps of gel, also arranged in these rows. If this sheet was pressed face down on the first sheet, the new lumps would fill the spaces connecting all the lumps together and allow the ions to flow. This, our scientists discovered, resulted in an electric charge of up to 110 volts of power. All good so far. But in order to get this result, the team had to use an incredibly large sheet of gel. And this was a bit of an issue because they wanted to create batteries small enough to fit inside our bodies. So, they enlisted the help of Magstein and Aaron Lamarou from the University of Michigan who came up with an ingenious solution, origami. I know, I bet you weren't expecting to hear that were you. But yes, that's right. It was origami, the Japanese art of folding paper, which held the key. By devising a special folding pattern for the sheet, which allowed the right gels to come into contact with each other in the right order, the scientists were able to make the battery much smaller without losing any power. We're talking about something small enough to fit into some snazzy, body compatible piece of tech, like an augmented contact lens, you know, the sort of thing you see in futuristic spy movies where crucial data is beamed directly into the eyes of our heroin or hero. Not only that, this battery would also be small enough to be used all over the body for devices like pacemakers, as I mentioned earlier. At the moment, this fleshy gel-powered battery can only work for around an hour before the levels of ions across all the gels equalize and the battery goes flat. But in the future, scientists believe there may be a way of harnessing the chemicals that naturally occur in our bodies to recharge the batteries. And if we could do this, well, just like electric eels, we'd be capable of generating our own electricity. And that would be a pretty shocking achievement. Head on over to the BBC World Service website now for more information on this episode. You can find it at BBCWorldService.com/30Animals. And in the next episode of 30 animals that made us smarter, I'll be hearing how the hairs of a polar bear are inspiring a new form of insulation. Don't forget to spread the word, it's #30Animals. Thanks for listening. (dramatic music)