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[♪ Intro] Spider silk is one of the world’s toughest materials. It is stretchy and incredibly strong, a combination that can outperform virtually any material that humans have made. And that is just the start of silk’s many remarkable properties.
To take advantage of them, scientists and engineers will need to figure out how to mass-produce something that can normally only come out of the body of a tiny organism. But if we can figure out how to reproduce it efficiently and sustainably, spider silk might just become one of the most important materials around. From replacing plastics to fending off plant pests, here are six amazing ways spider silk may one day be used to improve on existing human innovations.
Spiders have been using silk for around 380 million years, and have evolved at least eight kinds of silk for various uses. Such as dragline silk strands. They’re the ones that spiders use to rappel themselves from your ceiling while you lie in bed.
They’re not actually very sticky, unlike the strands used to ensnare prey. Drgline silk is made by the majority of spider species, beginning from when they are tiny spiderlings. They make and release this silk constantly, and it trails behind them as they go about their days.
Spiders attach it to surfaces as they travel along, and it acts as a continuous safety line in case they fall. One of the reasons it’s so strong is thanks to its semi-crystalline properties. As the silk is produced, some components of its proteins are crystallized, creating a hardened, strong fiber.
Scientists can use these super strong strands as inspiration to improve on and replace the synthetic materials we currently use, such as those in bulletproof vests or the cables supporting suspension bridges. That is, as long as we can figure out a way to practically reproduce it. And scientists getting close.
They’ve created genetically engineered bacteria to produce proteins like those found in spider silk. Unfortunately, the bacteria have a tendency to chop up the silk DNA sequence into smaller pieces. And those shorter strands of DNA result in smaller proteins.
Bigger proteins mean stronger silk, so recreating large enough silk proteins is key. But, more recently, a biosynthetic silk was created by adding a new sequence into the silk DNA, causing a chemical reaction that fuses the smaller proteins into larger ones. And, in 2021, this was improved even further, adding new properties into the already impressive silk-like material.
The result was even stronger and tougher than natural silk, while still maintaining its amazing stretching abilities. This is getting us one step closer to replacing a lot of our strongest materials, from steel to Kevlar. Now if you don’t associate spider silk with strength, you might think of it first and foremost as sticky.
Making it into a glue could really up the ante on current adhesives. For instance, spider silk could help better secure things to damp surfaces. After all, spiders don’t have the luxury of waiting around for a nice sunny day to catch a meal.
Roughly 3,000 species of spiders make orb webs like the one that you’re seeing right now. Within the web, different kinds of silk perform different roles. Much like dragline silk, stiff and tough silk strands absorb energy when something hits the web, while spirals made up of much more sticky silk are used to actually trap their prey.
These special strands are sticky thanks to a layer of glue along the silk that look like beaded droplets under a microscope. Each droplet has a liquid coating with a glycoprotein core, a unique combination of proteins that anchors the glue to the thread. And a key feature is that each strand has a lot of stretch in it, which forms a suspension bridge-like connection between captured prey and the silk thread.
This gluey stickiness, combined with the stiffness and strength of the silk strand, gives spiders an unparalleled adhesion that we could greatly benefit from. And while we have some pretty great glues out there already, spider silk is special because it stays sticky under wet conditions. Under humid or wet conditions, water permeates most materials, forming a non-adhesive layer between the sticky substance and the surface it’s supposed to be sticking to.
But it seems that certain proteins in spider silk have hygroscopic properties, meaning that they absorb moisture. Absorbing water into the strand itself stops droplets from forming as a layer between the silk and the spider’s prey, so the stick stays strong. Spider silk adhesion has also been found to work under super cold temperatures, which means we could depend on it to function in extreme environments.
Engineers are already working on powerful adhesives inspired by spiders, using water-soluble plastic polymers to create a hygroscopic sheath to mimic the absorbing properties of their silk. This lab-made, silk-mimicking glue keeps its stick at -196°C. Plus, it holds up even after violent shaking, splashing, and additional pressure from weight loading!
So, soon enough, you may finally be able to stick a label to a wet surface with success, even at -196°C! Many people have a fear of spiders, but humanity’s true animal enemies are the pests that eat our crops. This has led to the widespread use of insecticides to help keep crops healthy.
But while insecticides are effective, they come with significant risks, including the accidental death of beneficial invertebrates like pollinators, and even our friendly neighborhood spiders. So we might be better finding new ways to protect our crops. Rather than blithely killing pests, what if farmers could simply scare them away?
That’s a tactic taken by some plants, which use thread-like hairs to mimic spider webs! And, in a study focused on two common agricultural pests in North America, Japanese beetles and Mexican bean beetles, strands of silk were carefully placed along the leaves of snap beans. That alone acted as an insect deterrent.
Seeing as spiders are one of Earth’s most ubiquitous predators, it makes sense that other arthropods have evolved some ways to help detect one of their greatest enemies. Now, there’s plenty of work to do to make this practical; after all, it probably is not economical to individually place strands of silk on the leaves of every bean plant on Earth. But it points the way towards a potential strategy to deter agricultural pests in the future.
Another area spider silk might prove handy is in tackling humanity’s plastic problem. Plastic is an increasingly diverse and handy material, but we need to keep looking for more sustainable options. Combining spider silk with plant pulp might just be the answer the world needs.
Cellulose is the basic structure of the cell walls of plants. Grind up a plant, and you end up with nanofibrils, cellulose chains that are only a few nanometers in diameter. This nanocellulose is super versatile and fairly easy to obtain, but on its own it has limitations as a building material.
For instance, it can be quite brittle, so, a big no-no for a plastic replacement. To solve the brittleness problem, researchers in 2019 engineered protein sequences originally derived from dragline silk to make even better cellulose-based materials. Much like other studies, this was done by copying the structure of spider silk DNA, and using bacteria to reproduce it.
Then, these structurally-modified spider silk protein blocks were combined with cellulose blocks to make a structure that showcased the best of both worlds. A tough, stiff, and break-resistant material. Slightly different building blocks could be used to meet distinct requirements, kind of like how different types of plastics have such a wide range of properties and uses.
And unlike plastics, these materials will biodegrade, which means they don’t have the same detrimental long term effects of our current petrol-based products. It's not just silk’s strength and ability to biodegrade that makes it a desirable substance. Silk might actually improve how we see the world.
Literally. In truth, you are unlikely to directly experience spider silk inspired superlenses, since we’re not talking about binoculars or eyeglasses here. But improvements in nano-scale lenses would help advance fields where scientists need to make observations at a minute scale, like in microbial biology.
We have come a long way since the invention of the microscope, and we already have incredible nanoscopes that achieve extremely high resolution. But how clear an image they produce is limited by how well they focus light. Spider silk might be able to solve that problem.
The non-sticky web silk strands from both the Australian golden orb weaving spider and the long-bodied cellar spider have been shown to function like optical superlenses. The silk’s cylindrical shape helps it act as a tiny, transparent lens to concentrate an incoming beam of light very narrowly. .
Place a small section directly on top of a substrate, and voila, you have a magnifier. Since silk has powerful liquid collecting abilities, this can be harnessed to produce not only a cylindrical lens, but also a hemispherical magnifier called a dome microlens, which makes for an even clearer image. Resin dropped onto a strand of silk forms a teeny dome-shaped droplet, which is then coated in a gold nanolayer to further amplify the light.
This could really change the future of lenses, creating powerful and flexible imaging techniques for a wide range of applications. And in this case, it doesn’t appear that a synthetic equivalent would necessarily need to be created. Engineers just need to perfect the setup for using strands of extracted silk for this purpose.
Maybe nanotech labs will just purposefully house helpful spiders in the future to act as the ultimate lab assistants. While nanoscopes require extreme imaging precision, robots need to be designed with precise control over their motion, to ensure they can accomplish the task at hand. Robotic muscles need to produce enough force to carry out the required movement, like opening a valve, but also do it very precisely.
And a strange property of spider silk might help do just that. It turns out that spider silk supercontracts, meaning that it can rapidly shrink when moisture levels change. A study published in the journal Science Advances in 2019 described this accidental discovery.
Researchers learned that not only do the silk threads contract, but they also simultaneously twist. It appears that, under high humidity, water molecules disrupt molecular interactions between protein fibers in the silk strand, creating an asymmetry that triggers the twisting motion in one specific direction. And, as far as they can tell, other materials don’t do this, so it’s a really special discovery.
While the team wasn’t totally sure why exactly spider silk evolved this twisting, shrinking ability, they suspect it might have something to do with morning dew. This early morning moisture could trigger the web to be pulled tighter, ensuring it stays taut even as heavy droplets of dew weigh it down. This supercontraction characteristic could be used in robot design, where a specific motion would be very carefully controlled through changes in humidity.
But, of course, we’re a ways out from seeing this applied to machines, since the underlying mechanism is still not fully understood. First, scientists must unlock the secrets of this moisture-triggered reaction before engineers can even attempt to mimic it. While it is no easy task to create materials from spider silk, research on its incredible properties is so promising that it’s definitely worth the effort to figure out how to make these innovative ideas a reality.
The potential applications are so broad, spider silk might just become one of the most useful materials in our engineering toolkit. It highlights the importance of biomimicry, in which complex problems are solved by looking to nature for inspiration. Why reinvent the wheel when we can borrow spider technology to solve all our problems?
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