Giant spiders and the quest for bio-steel -- part 2

Credit: V&A

Spider sex may interest some specialists, but knowledge of spiders in the wider public mostly reduces down to two basic facts. They are scary, and they make webs. We've covered scary. Now it's time to look at their silk. Hong Kong's nephilas represent the most awesome web spinners in the spider world. Any footpath that falls out of use in spring will be festooned with golden orb webs very quickly, as I discovered on a hike on Lantau when I fell off the beaten path. As I followed the trail deeper into the hill side, the spider webs were cast closer to the ground, forcing me to duck lower. Each one inhabited by a dangling nephila, ready to sink her fangs into anything vaguely edible, like a human ear or a blindly placed finger. When webs hung too low I had to bash them with sticks, and I felt the surprising drag of the silk. 

    A nephila has six spinnerets at the end of its abdomen, which work to spin one of the strongest materials in the natural world. Protein molecules in liquid form are physically rearranged into a line of silk and squeezed out through tiny tubes. Seven different types of spider silk have been identified, each with a different quality to serve specific functions. These include strong radial spokes to support the main frame of the web, sticky orb lines to trap prey, draglines used during construction of the web, silk to entrap and wrap around struggling prey, soft lining material for egg sacks. 

    This versatile material is pound for pound five times stronger than steel, and three times stronger than Kevlar, the stuff of body armour and spaceships, according to online journal Chemical and Engineering News. Spiders spin it out in fine lines a tenth of the width of human hair, but a single strand can stop a speeding bee in mid flight.  A typical hiker is probably several thousand times bigger than a golden orb web spider but anyone who has bashed through a web can testify to the power of those microscopic spindles.  

    I once jumped through a web on a run. I took a short cut on a path that had been unused for some time because large bin bags obstructed the end of it. I accelerated to get a run-up to launch over the bags, only to fly face first into an enormous web. There was a large ripping sound, like wrenching fresh Velcro. Then a yell from me, followed by loud swearing. My first thought was to make sure the animal that wove the net was nowhere near my body. 

    I accelerated like Usain Bolt out of the starting block, and slapped myself raw. I never met the artisan but her silk wrapped me with an unnerving power, I was still peeling it off a mile down the road. 

    Spider silk clearly is something special and people around the world have made use of its properties for generations. It has been woven into nets to snare birds or clumped together into sticky balls to catch jumping fish. People have used it for bandages, stuffed into wounds to stem bleeding. A friend who grew up in Guangdong province told me how in childhood he would create a loop from reedy wood and scoop up a web into a ready made net. He used these to catch cicadas, which he would stuff with corn kernals, bake and eat. 

Spider inspired securitybot: reuters

    Today's materials scientists have said that finding a reliable source of the stuff is the “holy grail” of the textiles industry. It's not just the strength that is sought, it's also the flexibility of the line, being able to stretch to 40 percent of its length. On top of that, made from water and proteins, the stuff is a completely biodegradable natural material, a huge advantage over its polluting artificial rival, Kevlar, synthesized from nasty sulphuric acid. 

    Among the products lined up are lightweight body armour, parachutes, airbags, surgical sutures, artificial tendons, and even braking cables for fighter jets landing on aircraft carriers. But so far the quest to mass produce this wonder material to its full strength has remained elusive.

    The most obvious approach would be farming. Silk worm farming has gone on for centuries, making a huge cultural impact across the world. A quick count of nephilas on a Hong Kong hike would tell you that these awesome spiders are thriving. So how hard would it be to farm them? The answer so far is impossible. 

    The root of the problem lies in the very nature of spiders. They are cannibals and they do not cohabit. They instinctively know this from the moment they are born, their first task in life being to get away from their siblings as quickly as possible, before they get eaten, or they have to eat a brother or sister.  

    I had a demonstration of this one night when a huntsman egg sack burst open on my ceiling. I first noticed it when I switched on the light and looked up to see tiny specks spreading above me in all directions. Some spread horizontally while others were absailing downwards on tiny thread, like minute secret service assassins. There was a neat geometric pattern as the hundreds of spiderlings kept up a radiating equidistance from each other. My girlfriend was not amused, and I’m afraid that generation didn’t make it past nature’s first line of selective pressures, though I secretly hoped that one or two might have escaped to live well in a more welcoming home. 

    Farming requires cohabitation, and that doesn’t work for species that have a tendency to eat each other. But this didn’t stop an inspired French missionary in Madagascar from reviving a traditional nephila silk spinning machine in the 1880s. Father Jacob Paul Camboue, apparently turned to local folklore to create a device that could harness 24 spiders side-by-side in separate match-box pens. Their silk was "milked" by a hand driven winding crank, and woven into a workable thread. There is a record of a “complete set of bed hangings” made from spider silk, exhibited at the Paris Expo in 1898, although it isn’t known what happened to the sample set. 

    Some years back a group of textile experts fascinated by the qualities of spider silk built a replica of Comboue’s invention. Their painstaking work over four years produced an11ft by 4ft golden tapestry, manufactured from an estimated 1 million golden orb web spiders caught in the wild by 70 collectors.  The project leaders having thus demonstrated the impracticality of extracting silk at the rate of one ounce per 14,000 spiders bestowed the exquisite cloth to the American Museum of Natural History in New York in 2009     

     Now there is one major avenue of hope for those seeking the “holy grail” of spider silk, and that is in genetics. 

    Canadian start-up Nexia Biotechnologies, with an initial investment of $2.5 million, took up the quest for “biosteel” during the 1990s. Silk wasn’t the first product the firm focused on, but soon after spider DNA had been isolated, the enterprising laboratory turned its attention on the promise of manufacturing the world’s strongest natural material. They had strong backing from both the US and the Canadian defence agencies, keen to find a reliable source for future lightweight body armour, amongst other potential military uses.

    The big excitement came in 2000 when the company presented the world's first goats genetically modified with spider genes, irresistibly nicknamed the spider-goats. Goats may seem a strange choice, but they have the advantage of being compatible for farming, fast breeding and cheap. The technical reason for making spider-goats was that the mammary glands of goats are remarkably similar in structure to the silk producing glands in spiders, according to the scientists involved. 

    But in addition, the spider-goat was a marketing dream. It had to be, the juxtaposition of the dark mysterious arachnid with the thoroughly domesticated and humble goat had both comic and sinister overtones.  It already had a superhero precedent in spider man, which only fueled the incredible claims being made for the end product such as the inch thick cable that could suspend a jumbo jet. When the company floated on the stock market in December of the same year, the initial public offering fetched $42.4 million, one of the biggest hauls for a Canadian biotech IPO.

    The initial transgenic pair were, surprisingly, both males. But that worked, as they were able to successfully pass on their designer genes to new generations. The future looked good, too good to be true, and indeed there was a hitch.

A goat

    Three or four years down the line mass production still hadn’t started.  Despite the promise offered by similar mammary and silk producing glands, the spider goats didn't actually spin webs from their teats. Instead the silk proteins needed to be filtered out of the milk and purified into a white powder before being spun into thread. What is more goat silk was found to be only one-third of the strength of spider silk.

    A couple of years later, side-by-side with the the US Army, Nexia announced a welcome breakthrough in silk production, although cows had taken the place of goats, by providing the cells that became the source material for the production of artificial silk. With or without goats, there was, once again, great excitement about medical sutures, biodegradable fishing lines and soft body armour. It looked like commercial viability was on the horizon.

    But the next big announcement from Nexia came in 2004 and it went in a surprisingly different direction. It had nothing to do with spider goats or biosteel. Instead, working with the US Army’s Institute for Chemical Defense the company announced that transgenic goats had been successfully involved in experiments to protect animals from the effects of nerve gas. There were no super tough lightweight materials, no biodegradable suspension bridge cables, or even environmentally friendly fishing lines. Just a mysterious product called protexia, that could one day help soldiers withstand a chemical attack. 

    Two years later, Nexia had gone bust, and a herd of 40 unemployed “Franken-goats” were left on a farm in Canada. 

    Nexia failed, but the quest for artificial spider-silk is far from over. The University of Wyoming bought the goats in 2007, brought them to the United States, and continued to research ways of making spider silk a commercial viability.  The academic institution entered into a commercial deal with another biotech firm with a big idea, Kraig Labs. 

    Kraig announced in September 2010 that they had successfully engineered silk worms to carry spider genes. A product that doesn’t quite have the intrigue value of spider-goats, yet seems so inherently commonsensical that you can’t help but wonder why it took ten years to get from goats to silk worms. Initial results were promising with the relatively farmable silk worms producing spider enhanced high-grade silk. But the thread whilst doubling on the strength of un-tampered silk, hadn’t attained the power of spider thread. 

    The company has tinkered away at the quest over the years and continues to make promising announcements. To date it has created about 20 different types of spider silk fibers, with its lead product known as “monster silk,” a combination of spider and silkworm proteins and “significantly stronger and more flexible than commercial grade silk.” 

    But still that is not the elusive spider-strength threads of tomorrow’s body armor, bionic tendons and and suspension-bridge cables. 

    And so while humans may have invented nuclear power, genetic engineering and brain surgery, we still haven’t worked out how to mass-produce spider thread, a material so desirable that the strongest armies in the world have invested millions to crack its code. The holy grail remains unclaimed, for now.

Spider spinnerets. Credit: MicroAngela