Silk – with spider strength

N.C. biotech firm puts arachnid genes in silkworm eggs to create super spinners

CorrespondentApril 2, 2012 

Stumble into a sticky spider web and your first thought probably isn’t, “Someone should make cloth out of this.”

But David Brigham has made spider-silk fabric, and to hear him describe it, the stuff is close to magical. Spider silk, he says, has the potential to replace human tendons, help regrow organs and stop bullets.

Brigham is the scientist behind the Charlotte-based company EntoGenetics, which developing spider silk into a commercial product for medical, industrial and military customers. EntoGenetics last week announced the production of their first woven fabric that appears to be at least partly made of spider silk, and Brigham says he and company president Gary Lesley are talking with potential commercial partners. Lesley and Brigham have a vision of ex-tobacco fields being used one day to farm mulberry leaves to feed silkworms whose fiber is woven in North Carolina textile mills.

Spider silk’s great strength is well-known. Spider silk is five times as strong as steel, pound for pound.

But spiders aren’t exactly the most farm-friendly of creatures.

“First of all, they are cannibalistic,” Brigham says. “If you have five spiders in a cage, pretty soon you’ll have one fat spider. And they make tiny quantities of silk. And the other thing is – they bite.”

On the other hand, silkworms don’t bite people or devour each other and they are prodigious producers of silk. They’ve been bred for thousands of years to create fiber. And the domestic moths are flightless, so they can’t escape to become pests.

So Brigham has inserted part of a silk-making gene from a golden orb weaver spider into silkworms, so that the worms produce strands that appear to be part spider silk. The pale-ivory fabric woven from such silk, he says, is tough but “cloud-like.”

Challenge of size

But it was a long process from idea to fabric. First, Brigham, in conjunction with N.C. State University’s entomology lab, created a synthetic spider silk gene. “These are horrible genes to work with. They’re incredibly repetitive and the DNA makeup is different than anything we’ve worked with,” says Marce Lorenzen, an N.C. State assistant professor of entomology and principal investigator on the silkworm project. “What David has chosen to work with is the most challenging DNA of a spider to put into the most challenging part of a silkworm.”

Silkworm eggs are about the size of large poppy seeds, and Brigham had to use a needle that, at its tip, is the width of a human blood cell. Maneuvering it under a microscope, he slid the almost-invisible needle into each silkworm egg and deposited the new spider DNA. He did this hundreds of times. Yes, says Brigham, “it’s extremely tedious.” He’s working on a different method of gene insertion, which he won’t yet discuss, that he says will simplify the process.

After all the work, many of the resulting silkworms didn’t carry the new gene. And after those that did were bred together, just 25 percent of their offspring carried the necessary two copies of the spider gene in order to create a breeding population.

Finally, at EntoGenetics’ Polkton lab, enough spider-silk-spiked silkworms were alive and breeding to create the fuzzy cocoons Brigham needed to yield fiber. The N.C. State lab is testing the silkworms’ DNA to find out where in the worms’ chromosones the spider genes are located. But Brigham says the fiber that EntoGenetics’ silkworms made already is tougher than regular silk. It could be used for thinner, stronger medical sutures and textile applications, he says.

But his main goal is to beat Kevlar.

“We’re looking to be three to five times tougher – that’s how much energy the fiber absorbs – than Kevlar or Spectra,” Brigham says. Kevlar and Spectra are synthetics that currently are the gold standard for anti-ballistic fabrics. Brigham says pure spider silk can outperform both in terms of energy absorption, while also being lighter and more flexible.

The next step is inserting the complete strand of spider DNA into a silkworm – no easy task. “That is an immensely large gene,” Brigham says. “Imagine cooked spaghetti. If you have a one-inch piece of cooked spaghetti, you can push it around with your fork and make it do what you want. Very large pieces of DNA don’t work well, like full-length spaghetti.”

Brigham says spider silk’s potential is “breathtaking.”

“Somebody breaks an Achilles tendon on basketball court and they’re out for six months. You could replace that tendon with a spider-silk one and you could be walking as soon as staples are out,” he says. “You can use it for culturing organs. You can weave the silk into complex shapes then you can put stem cells in there and they can grow into ... whatever this thing I’ve woven is.”

Next: marketing

Gary Lesley, EntoGenetics’ newly hired president, says the company will need about $5 million in capital over the next three to five years.

“The funding strategy is to ideally find a strategic partner that’s already in the industry that would not only be a ready-made customer but a portal that is already connected with many, if not all, the potential market niches,” Lesley said. “There are a small number of entities like that not far from Charlotte. We’re in conversation with a small number of potential partners (and) later this spring we expect to announce the first major partner.”

EntoGenetics got some start-up funding from N.C. IDEA, a not-for-profit that gives seed money to new technology companies, and from Duke University and the N.C. Rural Development Center. More money came from the N.C. Biotechnology Center, Brigham’s friends and family and, as he put it, “a second mortgage on a house, cashing in a retirement fund and credit-card max-ing.”

EntoGenetics isn’t alone in the field. A Lansing, Mich.-based company, Kraig Biocraft Laboratories, also is pursuing spider-silk creation through genetically modified silkworms. Kraig Biocraft, which is publicly traded, also has yet to commercialize its product.

As for Brigham, he envisions turning former tobacco fields into mulberry tree plantations, with leaves being grown to feed to silkworms housed in abandoned textile plants whose fiber can be spun and woven in the state.

“That’s the goal – to not only eventually making it here, but reeling it and turning it into fabric here,” he says. “We may be able to pull off most of it, but I’m hoping for all of it.”

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