Scientists have found amazing uses for the humble spider silk, but it's really hard to procure.
Image: Peter Hartl/Flickr
Most people's knowledge of spider silk is limited to that moment when you accidentally walk right into a spiderweb and flip out trying to wipe that sticky, invisible mess off your face.
But it actually has some pretty incredible properties that researchers are trying to capture in order to build a better world, from superglues to medical implants.
"It's spun. It's not grown. That sets silks apart from all other natural materials," said Fritz Vollrath, a researcher at Oxford who is considered a pioneer in spider science. "Weight for weight, it's a lot stronger than even high-density steel and it's five times tougher than Kevlar."
Aside from being super-strong, spider silk is also remarkably flexible—it can stretch to 40 percent of its normal length before it snaps—and very lightweight. It's also biodegradable and biocompatible, which means it can interact seamlessly with living tissue (think medical procedures like artificial skin). It's pretty insane. So if spider silk so tough, flexible, and light, why aren't we making everything out of this wonder material?
Well, there are a few problems. For one, the silk itself, while very strong, flexible, and lightweight, isn't great for every application.
"You can't make a bulletproof vest out of it even though it's tougher than Kevlar. It would stop the bullet, but it would first go through your body because it's stretchy as well," Vollrath told me.
Also spiders only produce so much silk and they spin it themselves. It starts out as a protein in the spider's stomach which it spins into silk as it comes out of the body, so it's not like you can just crack 'em open and take out a spool of silky spider thread. It is possible to harvest the thread, but it's not easy. In 2009 a 11-foot by 4-foot gold cape made entirely of spider silk was completed. It was the largest textile ever created using only spider silk, but it took 82 people, four years, and more than 1 million spiders to make it. So, yeah, not a very practical process for mass production.
Instead of collecting spider silk straight from the source, scientists are studying ways of capturing the silk protein in order to produce the silk in other ways. Vollrath's team studies spider silk and finds ways to chemically manipulate silkworm silk (which is much easier to collect) to mimic the spider silk's best qualities. That silk can then be used to make strong, durable, and biocompatible medical applications like artificial skin and muscle grafts, Vollrath said.
"In those applications the toughness is no longer the issue, the biocompatibility is the issue," Vollrath said. "You find silks from a silkworm that has a good molecular composition. Then you modify it chemically to allow the functions you want it to do. For example, if you want to make bone you put hydroxyapatite [a naturally occurring form of calcium] against it and then start working with that."
Vollrath is using this process to develop ways of helping the body regenerate itself—the process for "making bone" he described could be used to help heal damaged joints and bones by giving the human cells a starting point to build off of. The same could be used for muscle or skin, all by tinkering with silkworm silk to make it more spidery.
Another option is to try to recreate the spider silk synthetically, which is what a team at Utah State University is working on. In February, UTU opened its new biomanufacturing institute where, among other things, it will be able to mass produce spider silk.
Researchers there have developed a process where they take a synthetic version of the spider gene that causes the spider to produce the silk protein and inject it into E. coli. The E. coli then produce the protein, which is more easily extracted from the bacterium than it is from the spider.
"We wash it off, precipitate it, freeze dry it and then it's ready to be dissolved to make fibers, gels, spray coatings, or whatever else you want to use it for," Randy Lewis, a biology professor at UTU, told me.
The process can be done on a large scale and Lewis and his team are aiming to find a path to the most practical way of capturing the unique properties of spider silks. The silk proteins they collect can be used to make a wide range of products, like hard-coatings and glues.
"Our adhesives are stronger than Gorilla Glue and Elmer's Glue and part of that is that they flex just a little bit before they rip loose. If you put it on wood, you'll actually rip the wood apart before you rip the glue apart," Lewis said.
But silk produced using this process still doesn't quite stack up to the spider's natural silk. Lewis said they are able to create fibers that are strong, but still only half to two-thirds as strong as a natural spider silk. They're investigating ways to improve the strength, but spiders have had a lot more time than humans to perfect the process.
"Spiders' systems have evolved over the course of the last 400 million years," Lewis said. Spiders are able to store the protein inside their bodies without it turning into a solid until the spider begins to spin the silk, for example, a process that is really hard to replicate in a lab.
"We don't know how they do it," Lewis said. "Nobody really knows how to make the solution that the protein is stored in. We make our own but it's clearly not exactly the same."
Lewis said in the future, synthetic spider silk will be used in everything from safety equipment to sporting goods to stitches, and we're getting close on a lot of those fronts. But when it comes to making amazingly tough silk exactly like the spider does, we just can't beat Charlotte.
This story is part of The Building Blocks of Everything, a series of science and technology stories on the theme of materials. Check out more here.