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Bolt Threads

Spinning synthetic spider silk into wearable textiles

by Alex Scott
November 2, 2015 | A version of this story appeared in Volume 93, Issue 43


Pilot fermentation facility.
Credit: Bolt Threads
Bolt Threads makes spider silk using genetically modified yeast in industrial fermenters such as the pilot-scale one shown here.

Imagine a fiber five times as strong as steel but softer than wool. It sounds like something a superhero would wear, but chemist Dan Widmaier is well on his way to making that fantastical fiber a reality. In 2010, Widmaier cofounded Bolt Threads with the left-field idea of developing an inexpensive way to produce synthetic spider silk.

Bolt Threads

Launched: 2010

Location: Emeryville, Calif.

Focus: Affordable synthetic spider silk

Technology: Yeast engineered to generate spider silk protein that can be spun into yarn

Founders: Dan Widmaier, David Breslauer, and Ethan Mirsky

Funding: $40 million from Foundation Capital and Formation 8

Widmaier’s idea isn’t novel. Scientists have spent the past two decades trying to figure out the chemistry and biology of making synthetic spider silk that can be spun into yarn. Bolt’s scientists may finally have cracked nature’s code: The company expects its spider silk process will be ready for commercial rollout next year. If successful in hitting that goal, it will likely be the first company to get a spider silk fabric onto the market.

Bolt’s scientists use recombinant technology to modify the genetic code of spider genes that make silk proteins and insert them into a strain of yeast. Fed with sugar and water and left to ferment, the yeast expresses the spider silk protein. The company can tune the properties of the silk—making it, for example, stretchier or stronger—based on the genes inserted into the yeast.

After some processing steps, the silk protein is converted into yarn through a wet-spinning system similar to what’s used to spin acrylic and rayon fibers.

Other firms are also racing to commercialize spider silk fiber. Ann Arbor, Mich.-based Kraig Biocraft Laboratories says it’s collaborating with textile companies to make woven products using its hybrid silkworm-spider silk fiber, which is produced by silkworms modified with spider DNA.

And Germany’s AMSilk has been producing spider silk protein for applications such as shampoos and cosmetics since early 2014. But so far it has failed to come up with a commercial process for making yarn with the right mechanical properties and the right price.

Credit: Bolt Threads
David Breslauer (left), Widmaier, and Ethan Mirsky.
Bolt threads team.
Credit: Bolt Threads
David Breslauer (left), Widmaier, and Ethan Mirsky.

Bolt isn’t daunted by the competition. The company says its process is ready for commercialization. A U.S.-based custom manufacturer will supply the protein, and the company is exploring both internal and external options for spinning.

Moreover, Bolt expects its spinning process to yield spider silk yarn at a price of less than $100 per kg—a level the company believes will allow it to compete with fine-quality natural fibers such as cashmere, silk, and mohair. “We’re very confident that our economics are significantly better than previous efforts to commercialize spider silk,” Widmaier says.

Investors share Bolt’s confidence. During its first few years, the company secured $40 million in funding from Foundation Capital and Formation 8—a sum that dwarfs the money raised by other spider silk firms. Bolt has used some of the cash to build a team of researchers; today the firm has 50 employees, almost all of whom are scientists.

Bolt plans to start spinning yarn commercially by 2016. If successful, we may soon be ditching our polyester, wool, or cotton garments for the novel experience of pulling on clothes made from spider silk.

Find out what Bolt Threads has been up to since it appeared on C&EN’s 2015 Top Start-ups List by clicking here.


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