Spider Silk

An NC biotech company is using spider DNA to transform silkworms to produce spider silk: a fiber tougher, lighter and more flexible than most fibers.

CHARLOTTE — The building is rather plain: metal-sided, metal-roofed and industrial. Which is appropriate, as it sits on the edge of an industrial park in Charlotte. The sign on the door indicates that the building belongs to a company called Entogenetics. And what’s happening inside could signal the end of the search for the ultimate textile target.

“This is a cocoon and in fact these are all cocoons for silk worms,” says David Brigham, founder and CEO of Entogenetics as he reaches into a box filled with white, oval shaped objects that are smaller than eggs.  They are also fuzzy. He pulls a tiny thread off of one of the cocoons.

“As you can see, this is smaller than the hair on your head, but this is a one mile long, continuous strand of fiber,” he adds.

Silk has been collected from the cocoon of the silk worm for thousands of years. The material is prized for its beauty and texture. But these are not the cocoons of typical silk worms.

Brigham opens the door of a small room built from plastic sheets draped over a metal structure, which stands in the middle of the building. Inside the room, is a series of metal shelves lining each side. On the shelves sit plastic dishes containing large mulberry leaves. Taking a closer look, you can see tiny worms crawling on the leaves in one of the dishes.

“This one right here—one of the parents tested out at full strength spider silk,” Brigham says as he points to the dish excitedly. “So I have high hopes for these little guys and they just hatched this morning."

Read that last sentence again. Spider silk, from silk worms?

“I know, it sounds unusual," offers Brigham, "but we’re taking the black widow gene, and putting it in place of the silk worm silk gene,” he explains. “So when they go to make cocoons, they read it and make it, and instead of making regular silk they make spider silk.”

The spider Brigham and his company are using in their experiments is the black widow spider. Yes, this spider has somewhat of a creepy association, and its bite can be deadly, but the black widow produces a silk that is stronger and stiffer than most spiders. Brigham implants the gene that controls the production of that stronger and stiffer black widow spider silk, into the silkworm.

It doesn’t appear that the silkworm knows the difference. The tiny worms hatch; they eat mulberry leaves and grow up to be big and fat. As they begin the process of turning into a moth, they spin a cocoon and turn into a pupa. But at that point the process is interrupted because the cocoons are harvested to make yarn and fabric.

You could call it agricultural alchemy. Since silk is a natural protein fiber, putting the spider gene into the silk worm transforms the worm into a kind of protein factory for spider silk. The silkworm doesn’t change and as mentioned it behaves the same. But thanks to genetic engineering it’s just making a different silk. Mother nature should take care of the rest.

“The engineered silk worms have been tested to see if they have the spider gene and they do,” explains Brigham. “However right now it is only one copy, so we’re breeding transformed silkworms together and they should have two copies, which will mean they will produce full strength spider silk.”

But for all of the high-tech genetics involved in creating spider silk this way, the irony is that the silk is still harvested in essentially the same way the cocoons of silk worms have been harvested for thousands of years.

The cocoons are dunked into hot water to loosen up the protein glue that holds the fibers together. After a minute or so has passed, Brigham takes a brush and begins to swirl it around in the water.

“So we should have loosened up the glue enough that we can swirl this around get one of the fibers,” Brigham says, as he snags a fiber with the brush and then grabs hold of it and starts to pull. “And so now we are unreeling the silk.”

But because the individual fibers are so thin, it is impossible to run each fiber through a textile mill. That means multiple fibers are combined and loaded onto the mill at the same time. The number of fibers depends on how fine a fabric you are making.

The cocoons, with the ends of the fibers now exposed, are brought to a textile mill reeler. The tiny fibers are then combined, one by one, by one, and loaded onto the mill. The machine will automatically unwind that one-mile long strand of silk from each cocoon. By now you’re probably asking, why exactly make spider silk? Well, because it’s so strong.

“Spider silk is five times tougher than Kevlar,” explains Brigham. “There is not as much strength, but there is plenty of stretch and that’s the key.”

Brigham uses the analogy involving a plate glass window, a trampoline and Hall of Fame pitcher Nolan Ryan.

“If you put Nolan Ryan in front of a plate glass window and ask him to throw a ball at it, you’ll be ok for a while, but eventually he’ll throw a ball through the window,” says Brigham. “But nobody, not even Nolan Ryan, throws a ball through a trampoline. Kevlar is the window and spider silk is the trampoline.”

The military is searching for a material that is not only strong but also more elastic and lightweight. The spider silk would be added to body armor. Brigham’s creation has already undergone ballistic testing. It passed until the most extreme of tests when experimenters increased the caliber of shells targeting the material until it was finally defeated. The military wanted to see what it would take to fail, and they were happy with what they found.

The fiber could also be used in a host of medical applications such as sutures, implant coatings or even as artificial tendons. That’s because the human body doesn’t reject spider silk.

There’s still much more testing to go. But as he watches the reel of spider silk grow on the milling machine, Brigham smiles, knowing he could be on the brink of an amazing discovery.

“It works every time," he says, tracing the path of the silk from the cocoon to the reel. “I’m not a farmer, but I’m taking leaves, turning them into big silk works, and turning the product of my agricultural labor into super strong yarn, that is going to save lives. It works every time!”



Related Resources: