Worms with spider genes spin silk tougher than bulletproof Kevlar

Spider silk is stretchy, strong, and tough. But genetically engineering a more cooperative organism to produce it has proved elusive. Now, researchers have used gene editing to make silkworms that can spin spider fibers tougher than the Kevlar used in bulletproof vests.

The material, described today in Matter, is “a really high-performance fiber,” says Justin Jones, a biologist who engineers spider silks at Utah State University but who was not involved with the research. It could be used to make lightweight but tough structural materials for fuel-efficient planes and cars, he says, wound dressings for faster healing, and superthin but tough sutures for eye surgeries.

People have been cultivating silkworms for thousands of years, unwinding their cocoons to provide material for textiles. But their silk breaks easily. Spiders have the opposite problem: They make incredible silks, but the arachnids are hard to cultivate. One hundred silkworms can hang around peaceably in a small space, whereas 100 confined spiders will attack one another, until only one or two are left alive.

In an attempt to harness the best of both animals, researchers have tried for years to genetically engineer silkworms to make spider fibers. But spider silk proteins are large, and the correspondingly large genes have been difficult to insert in the genomes of other animals.

So in the new study, Junpeng Mi, a biotechnologist at Donghua University, and colleagues chose to work with a relatively small spider silk protein. Called MiSp, it’s found in Araneus ventricosus, an orb-weaving spider found in East Asia. The scientists used CRISPR to insert MiSp in place of the gene in silkworms that codes for their primary silk protein. But the scientists retained some silkworm sequences in their MiSp gene construct, Mi says, in order to ensure the worm’s internal machinery could still work with the spider protein.

The transgenic silkworms produce fibers with high strength—a measure of how much stress a material can take without deforming—and high toughness—a measure of how much energy it can absorb through stretching before rupturing. The fibers were almost as tough as the strongest natural spider silk, and about six times tougher than Kevlar.

Jones says it’s surprising that the MiSp-based fibers were so flexible. This protein typically makes for strong, but not stretchy, fibers, he says. “But it does make a flexible fiber when you put it in a silkworm.”

To commercially produce the spider silk fibers, Mi says he and his colleagues will need to cross-breed their research-grade silkworms with commercial strains that are used for large-scale silk cultivation. He says the fibers, which are biodegradable, might find first use in surgical sutures.

Jones notes it could be challenging to protect intellectual property rights when commercializing the spider silk because it would likely entail distributing transgenic silkworm eggs to many farmers. It also remains to be seen, he says, whether the inserted genes will persist when the silkworms are bred.

Next, Mi wants to see whether he can engineer silkworms to make spider silks that are even stronger and stretchier. Mi is thinking about designing silk proteins that incorporate nonnatural amino acids, which he says has “boundless potential” to enable silks with totally new properties—perhaps one not only tougher than Kevlar, but stronger, too.