Why Spider Silk is Stronger Than Steel

This vibrant cape and shawl are the largest pieces of cloth to ever be made from spider silk. Over the course of three years, it took a team of about 100 people in the highlands of Madagascar to collect the silk, spin the threads, weave the fibers, and embroider the details. In the end, 1.2 million golden orb weaver spiders, each producing 30 to 50 meters of yellow thread, were used to create this masterpiece before being released back into the wild. But why would anyone go to this amount of trouble to make something out of such a strange and difficult to obtain material? Because spider silk has what seems to be almost magical properties. For thousands of years, humans have been fascinated by this material. The ancient Greeks used cobwebs to treat wounds, and traditional hunters in the South Pacific used spider silk to catch fish, where the spider silk fibers get stuck in the fish's serrated teeth and they are unable to tear through due to the silk's strength. To be able to withstand impact forces from flying insects without breaking, spider silk has evolved to be even more flexible than man-made nylon. It's biocompatible and biodegradable, and on a per-weight basis, spider silk is even stronger than steel. And now, spider silk is attracting the attention of geneticists, biochemists, and material scientists who are working to unravel the mystery of its incredible properties. What is it about spider silk that makes it so flexible, so durable, and so strong? Just how strong is it? And will we ever be able to harness this power for ourselves? For spiders, making such a material is just part of their biology. The earliest known proto-spider lived about 380 million years ago, during the Devonian period, and were among the first creatures to live on land. This spider had the classic thin waist and abdominal segmentation of the modern spider. These early spiders also had spinnerets, which is the organ that produces silk. However, their spinnerets were located in the middle of the abdomen instead of at the end of the abdomen, like in modern spiders. This means that instead of weaving webs, they most likely used their silk in sheets to cover their eggs or line their burrows. It wasn't until about 250 million years ago that spiders with spinnerets at the end of their abdomen appeared, allowing for more elaborate silk creations. Not all spiders are able to make intricately patterned webs like these, but the ones that can do so masterfully. Of the 45,000 or so species of spiders, about 12,500 species are orb weavers. The builders of the spiral, wheel-shaped webs often found in gardens, fields, and forests. The creation of the silk begins in the spider's silk glands and the spinnerets located on the posterior end of their abdomen. Inside the glands, the silk starts out as liquid. As it travels down the cavity to the spigots, a combination of water extraction, acid, and tension turns it into its final solid silk form. This silk then travels through the spinnerets, where it's spun into a fiber. Orb weavers produce at least seven different kinds of silk. Silk from the major ampullate is the structural silk, like the bridge line and the radial spokes. Then there's silk from the flagelliform gland, which makes the spiral. Then there's the aggregate silk, which creates the But of the many types, the most extensively studied is dragline silk, aka the spider's lifeline. Dragline silk enables the spider to hang from ceilings and serves as a constant connection to the web, allowing it to drop away if it's in danger. And this particular silk is perhaps the most remarkable material from the natural world. When it comes to its strength, many comparisons are made between spider silk and steel, and for good reason. Dragline silk combines toughness, strength, and elasticity to an extraordinary degree. It's a composite material composed of two different proteins, spidroin 1 and spidroin 2. Each protein contains an amorphous, non-crystalline matrix. This is the stretchable part of the silk that gives it its elasticity. Then, embedded in the amorphous portions are crystalline regions that link together and toughen the silk. It's certainly an impressive material, but do the steel comparisons really hold up? Can this delicate, natural material really have a similar strength to the material we build bridges and skyscrapers out of? To get to the bottom of this claim, we first need to understand what the meaning of the word strength even is. There are different types of material properties that define how a material will respond to different types of stress. There's things like toughness, a material's ability to resist damage from impacts. Glass, for example, has low toughness and shatters when smashed with a hammer. Rubber, on the other hand, can completely withstand a similar blow. Then there's compressive strength, the ability to withstand being pushed together before being compressed, crushed, or buckling. And stiffness, a material's ability to resist being deformed. For properties like stiffness, spider silk is nowhere close to steel. But there is one area where spider silk particularly excels, and it's tensile strength, the resistance to breaking under tension. Tensile strength is measured in pascals, the pressure of one newton per square meter. And for a material that seems rather delicate, it surprisingly has a similar or sometimes even better tensile strength than steel. There are many different types of steel, and thus tensile strength of steel can wildly vary, up to 2.5 gigapascals for certain specialized steel composites. But let's look at the most common type of steel used in construction, mild steel or plain carbon steel. On average, mild steel has a tensile strength of 0.4 gigapascals. And while spider silk's tensile strength can also vary, one of the strongest spider silks comes from the golden orb spider, which has a tensile strength of up to 1.6 gigapascals. When measuring tensile strength, the diameter of the material is accounted for, which means a hair-like strand, a pencil-width strand, or a thick beam of the same material will have the exact same tensile strength. This means a single strand of spider silk can outperform many types of steel of the same diameter. This is impressive enough, but when you consider the densities of each material, it's even more so. Spider silk is about one-sixth as dense as steel. This means a strand of silk is much stronger for its weight than steel is. Another area where spider silk excels is its ductility, its ability to be stretched and deformed without breaking. Therefore, its toughness, the area under the stress-strain curve, is remarkably high, higher than even Kevlar. And for spiders, this level of strength and flexibility is essential to their survival. When an insect strikes their web, the stretching of the matrix enables the web to withstand the impact of the flying prey. Over hundreds of millions of years, these properties were favored during the process of natural selection, giving us the extraordinary material we know today. Its potential uses in textiles, medicine, and even aviation are boundless. And so it's no surprise that now scientists are working tirelessly to recreate it. If spider silk is so incredible, why don't we have ropes, cables, parachutes, or nets made from this super strong, super lightweight material? Because the mass production of spider silk is incredibly challenging. Trying to farm them at scale has been attempted and proven to be basically impossible. Spiders are carnivorous animals that don't like to live in groups, as it results in large-scale cannibalism. But collecting, milking, and then releasing wild spiders is also a huge challenge. Collecting the amount of silk needed to make anything of significance takes a very long time, such as the three years it took to make one cape and shawl. So for these reasons, scientists are looking to recreate it themselves. One common method is to genetically modify a different host organism to produce spider silk proteins. This is a great idea, but historically, there has been one major problem with recreating spider silk. It has been very difficult to find a way to produce large enough proteins. And large proteins are important. The tensile strength and toughness of spider silk are positively correlated with its molecular weight. The bigger the molecule, the stronger the silk. So because of this, scientists turned to plants. Plants already have the genetic capacity to make large proteins. And since agriculture is easy to scale up, silk, in theory, could be produced and harvested in mass quantities. However, the proteins plants make are not as large as what spiders produce, meaning the silk spun from them will have a less repetitive protein structure and won't be as high quality. So scientists set their sights on a different host, something that can easily create high amounts of spider silk, but is perhaps a bit unexpected. Goats. Domesticated mammals already naturally produce large volumes of protein-rich milk. By targeting the gene for milk protein, genetically modified spider goats can produce spider silk proteins in their milk. First attempts at this method were promising. The milk contained significant quantities of spider silk proteins. However, the size of the proteins was still too small, just 65 kilodaltons, compared to spider silk's 350. So scientists turned to silkworms. They offer a great advantage. Since they already have the necessary spinning apparatus needed to turn silk proteins into silk, inefficient artificial spinning methods aren't needed. Studies have found that modified silkworms can produce large amounts of spider silk, with their resulting silk content consisting of 35% spider silk protein. But spider silk made from modified silkworms isn't perfect. The protein is still smaller than natural spider silk proteins, resulting in mechanical properties that fall behind natural spider silk. But perhaps the most promising method yet, a method capable of making the biggest proteins, comes from something much smaller. Genetically modified bacteria can be used to create large amounts of a desired protein. Because the bacteria E. coli replicates itself pretty quickly, a large modified colony could be made in no time. However, E. coli too has some limitations. This small bacteria did not evolve to make proteins as large as spider silk proteins. In spiders, the genetic sequence that codes for long chains of proteins has many repeating sections. The more repetitions of the sequence, the bigger the resulting protein. So using that logic, researchers inserted a similarly long repeating sequence into their bacterial host. But there's one problem. After the DNA sequence reaches a certain size, the bacteria can't handle it. They chop the sequence into smaller pieces so that the resulting protein doesn't get too large. But in 2018, scientists found a workaround. They added a short genetic sequence to the silk DNA that promotes a chemical reaction between the resulting proteins, fusing them together to form a bigger protein. This method was so effective that the resulting proteins were larger than anyone's ever been able to make. In fact, they were larger than most natural spider proteins at 556 kilodaltons. Once the proteins are collected, they can be spun into fibers with properties similar to natural spider silk. But the process still has some drawbacks. Mostly that the spinning process is hard to replicate. The transformation from a liquid state inside the silk glands to a solid state outside of the spigots is pretty complicated. But scientists have figured out that a sudden drop in pH, a particular salt concentration, and shear forces allow the spider silk to materialize. By mimicking these conditions, scientists are getting close to an artificial spinning process that's as good as the real thing. So far, every group that's attempted to produce enough spider silk to bring it to the mass market has failed. But with these recent advances, spider silk may very well soon replace petroleum-based synthetic fibers used in many industries. In 2016, AmSilk collaborated with Adidas to develop a concept sneaker, and Omega recently created a special edition spider silk watch strap. Airbus is also exploring how it can be used in aviation. It soon could take on a role much like carbon fiber in today's world. It's one of the best examples of innovation inspired by nature. By looking closely at nature's best ideas, we start to see that the answers to our toughest problems are all around us. Spiders are not exactly everyone's favorite animal, which is understandable. But it's easy to put aside the heebie-jeebie factor when you think of their remarkable evolution and their place in the intricate web of life. Spiders, ants, termites. These bugs that we may overlook or downright despise are actually some of nature's best engineers. Researchers are looking to termites now, for example, to understand how they build massive structures using a process called biocementation, where grains of soil are fused together into small balls with moisture, saliva, and excretion. Basically a process of construction using their own type of bricks. These structures also maintain a constant temperature and humidity inside while still ventilating the underground nests. It's an absolute wonder of nature. And human engineers are now trying to replicate this type of architecture. To see firsthand how the termites build their mounds, and to understand the surprising difficulty with studying these insects, you should watch Termites the Inner Sanctum on CuriosityStream. It's a 45 minute in-depth film that takes you from Borneo to Africa to inside the deepest, hardest to reach chambers of their nests. It's one of many detailed and beautiful nature films on CuriosityStream that will teach you about a corner of evolution that you might not have considered before. Alone, CuriosityStream is a fantastic educational streaming platform. But now, CuriosityStream has partnered with us to offer an even better package. By signing up to CuriosityStream, you now also get a subscription to Nebula. Nebula is a streaming platform made by me and several other educational YouTube content creators. It's a place where we can upload our videos ad-free, and a place where we can experiment with new, original content. We have so much new, exclusive content planned for Nebula in the new year, like a real science series on human evolution, and Real Engineering's upcoming new series, The Battle of Britain. And right now, the bundled deal is at a hugely discounted price. For just $11.59, you get access to both CuriosityStream and Nebula for the entire year. That's 42% off the usual price, and means you're getting both services for less than a dollar per month. This deal will only last for a few more days, so don't hesitate for too long. Signing up is also the single best way you can support this channel. It helps us to keep growing, and helps us to bring you more and more new content. So go to curiositystream.com slash real science to get in on this incredible deal. And if you're looking for something else to watch right now, you can watch our previous video, The Insane Biology of the Orca, or watch Real Engineering's latest video about the engineering of the James Webb Telescope.