Bridges made of spider silk? You can thank the goats for that.
Put simply, arachnids are amazing. For example, there are over 2,000 species of scorpions on Earth, and all of these species fluoresce under ultraviolet light (Why? Who knows?!?). Meanwhile, Harvestmen, also known as daddy long-legs, have scarcely changed at all during 305 million years of evolution, and they can detach their own legs to distract would-be predators. And besides being the primary vector for Lyme disease transmission to humans, black-legged ticks can live up to two years and eat just three times during their entire life cycle.
But perhaps the most amazing arachnids of all are spiders, who have managed to delegate the production of one of the strongest materials known to man, silk, to goats!
More precisely, these days, there are genetically modified goats that produce milk with spider silk in it. Spider silk is part of a class of materials known as biopolymers, which are protein-based materials of biological origin. Spider silk has attracted widespread interest from engineers in recent years, largely because of its impressive mechanical properties — stronger than steel yet thinner than a human hair. It’s not a new material, though. Fossil records indicate that spider silk has a history on Earth dating back to the Middle Devonion Period over 350 million years ago!
One possible application of spider silk is as a cost-effective alternative to Kevlar. Kevlar fibers, originally engineered by DuPont in 1965, can be up to 20 times stronger than steel and have been widely adopted in bullet-proof vests and underwater tethering cables. But its production is expensive. So why not instead use spider silk — the biological equivalent to Kevlar fibers — and let nature take care of the manufacturing? The problem is that spiders are small creatures, so gathering large amounts of silk from them is a time-consuming and tricky process. For instance, it took 70 people a total of four years and a million golden orb spiders from Madagascar to gather enough silk to spin an 11 x 4 ft tapestry, which is now hanging in the American Natural History Museum (reported in Wired; AMNH webpage here).
Which brings us back to goats. Silk-producing goats were originally engineered and owned by Canadian company Nexia Biotechnologies Ltd. The early half of the 2000s saw a lot of hopeful press coverage over Nexia’s famed BioSteel, a spider silk-based material. By 2009, however, the goats had all but disappeared from headlines. Nexia had failed to bring BioSteel to market, and the company disbanded and sold its assets, including its herd of silk-producing goats.
In the meantime, a competitor to silk-producing goats emerged: hagfish. Hagfish, it turns out, produce a similar protein to spider silk in terms of mechanical properties. In the late 2000s, researchers at Shoals Marine Lab reported that the hagfish protein, which the fish exude in their slime, is less biologically complex than spider silk, in principle making it cheaper for large-scale production.
Despite their competition, today, silk-producing goats are making a comeback — this time, without Nexia. Largely, this has been due to the work of Professor Randy Lewis at Utah State University, who has developed a particularly successful breed of so-called “spider goats” at a university-run farm. Watch a recent BBC video here to meet Freckles, Pudding, and Sweetie — part of Lewis’ herd of 30 spider goats. Lewis’ team is also pursuing spider silk production in transgenic bacteria.
Silk products, like other engineered materials or fiber-reinforced composites, have the potential to revolutionize materials for ultra-demanding applications like bridges, medical sutures, and car bodies. (I can also think of a certain crime-fighting vigilante who might be in the market for a new red and blue suit!) In the end, one thing is clear—scientists and engineers remain fascinated with the material and its potential applications. Then again, what self-respecting science geek wouldn’t be? So, keep your eyes peeled in the future for more spider silk news!