For the first time, scientists have successfully produced full-length spider silk fibers using genetically modified silkworms. The silk's high strength and toughness promise to be a scalable, sustainable and better alternative to existing synthetic fibers such as nylon. First author Mi Junpeng, a researcher at the School of Bioscience and Medical Engineering at Donghua University in China, said: "Silk silk is currently the only animal silk fiber that is commercialized on a large scale and has perfect breeding technology. Therefore, using genetically modified silkworms to produce spider silk fiber can achieve low-cost, large-scale commercialization."

The fiber that silkworms use to spin their cocoons has been cultivated for thousands of years, but although this fiber is abundant, it has a reputation for being brittle. Spiders, meanwhile, produce enviably tough silk, but cultivating it on a large scale has always been out of reach. The researchers pointed out that "the carnivorous nature of spiders makes it impossible for spiders to live together, otherwise almost all individuals will fight to the death."

This latest research offers the best of both worlds, changing the way this elusive natural material is produced sustainably. Scientists have been trying to perfect this bionic "recipe" for more than a decade.

To engineer silkworms with unique spider senses, Mi and colleagues focused on a small silk protein from the East Asian orbiting spider Araneus ventricosus. Using CRISPR-Cas9 technology, the MiSp protein was inserted into the DNA of silkworms, replacing the gene encoding the main silk protein of silkworms.

The scientists also achieved "targeting" and successfully activated genes in the silkworm's DNA without interfering with any other aspect of the silkworm's natural silk production.

"The 'positioning' concept proposed in this paper, as well as the minimal structural model proposed, is a major breakthrough from previous research," Mi said. "We believe that large-scale commercialization is just around the corner."

The resulting fibers exceeded the researchers' expectations, exhibiting high tensile strength (1,299 MPa) and toughness (319 MJ/m3). Not only that, but the fiber was far more flexible than expected; MiSp protein is known for producing silk that is strong but not stretchy.

"Spider silk is a strategic resource that is in urgent need of development. The fiber produced in this study has extremely high mechanical properties and has great potential in this field. This fiber can be used as surgical sutures to meet the needs of more than 300 million surgeries worldwide every year."

The new fibers have broad commercial potential, including smart materials for the military, aerospace technology, biomedical engineering and clothing. The resulting silk is six times stronger than the Kevlar used in bulletproof vests.

The researchers now plan to develop genetically modified silkworms that use natural and engineered amino acids to produce spider silk fibers. Mi said: "The introduction of more than one hundred engineered amino acids has brought unlimited potential to engineered spider silk fibers."

The research was published in the journal Matter.