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Spinning Synthetic Spider Silk

A California company may have figured out how to use genetic engineering to make extremely versatile fibers the way spiders can.

Materials scientists have spent decades trying to mimic spider silk. Not only are some of these silks stronger than steel, but they have combinations of properties not found in synthetic fibers like the Kevlar used for bulletproof vests or the petroleum-based polyester found in clothes.

Top: Dan Widmaier
Bottom: David Breslauer

But while several companies have produced artificial silk for small-scale applications, it can’t be widely used to create new kinds of tough, durable, lightweight, petroleum-free materials unless it can be made in very large volumes. A startup called Bolt Threads, in Emeryville, California, might have found a way.

Two of its founders are Dan Widmaier and David Breslauer, who have been working on the problem since they were grad students at the University of California, San Francisco, and UC Berkeley in 2007. They use synthetic-­biology techniques to engineer proteins that can be spun into fibers with properties they can alter depending on their customers’ needs.

That versatility is crucial. While synthetic fibers made from petroleum tend to be good at one thing, silk can be reëngineered to suit diverse applications. Spiders themselves do this, fine-tuning their silk to make strong structural struts for their webs, sticky spots to capture prey, and a tough line to hang from.

At Bolt Threads, genetically engineered yeast brew silk proteins that can be spun into fibers. The properties of those fibers can be altered by tinkering with the protein concentration and the temperature, tension, and other aspects of the spinning process.

1. Inside this fermenting tank, genetically engineered yeast produce spider-silk proteins.
2. The yeast feed on sugary feedstocks such as this dextrose.
3. In a research-scale fermenter within a glass beaker, different growing conditions or proteins are tested.
4-5. Bolt’s ultimate goal is to make fibers to customers’ specifications. The first step is designing a new silk protein and engineering yeast that can produce it, like these experimental yeast inside an incubator and on petri dishes.

6. Purified spider-silk proteins are ready to be made into fibers.
7. Part of the fiber-making apparatus. During the spinning process, fibers are extruded from a solution of protein, run through baths, and dried.
8. This machine is used to test the mechanical strength of experimental fibers.

9. After being spun and treated, the silk fibers are spooled.
10. Breslauer holds threads of artificial spider silk, ready to be woven into textiles.

The company says its first products will be in consumer apparel in 2016. Its fibers, which are much finer than natural materials like cotton and stronger than nylon, could lend clothes the best qualities of both natural and artificial fibers: they would be soft and light, while durable enough to toss in the wash repeatedly. However, the company won’t specify which properties it aims to achieve in its early products.

Widmaier and Breslauer do say, however, that clothes are only the beginning—an application that proves the company can manufacture at large volumes. “If we can get it to that scale,” Widmaier says, “we can do anything.”

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