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Genetically Modified Silkworms Produce Spider Silk Six Times Tougher Than Kevlar

A spider web, covered in morning dew, hangs below a handrail post at sunrise.
Credit: Kuaileqie RE / Unsplash.
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For the first time, researchers have genetically modified common silkworms to produce full-length spider silk proteins. Such proteins can be used to produce fibers that are six times tougher than the Kevlar fiber used in bulletproof vests.

Published in the journal Matter, the researchers say these findings could help to pave the way for spider silk’s commercialization, ending the current reliance on less sustainable synthetic fibers. With spider silk’s favorable tensile strength and toughness, they also believe this could lead to the development of super materials.

Finding an alternative to synthetic fabrics

The textile industry has a bit of a sustainability problem. While cotton, jute, hemp and other natural fibers can be worked into textiles for clothing and other applications, synthetic fabrics remain hugely popular.

Recent estimates suggest that around 60% of clothing is made from synthetic fiber, including polyester, acrylic and other plastic-based materials. The unique physical properties of these synthetic fabrics have led to them being adopted more widely for specialist applications, such as Kevlar fiber in bulletproof vests and synthetic rubber for neoprene sportswear.

Such commercial synthetic fabrics are notoriously bad for the environment. The European Parliament estimates that the laundering of clothes made from synthetic fabrics accounts for roughly 35% of the primary microplastics that are released into the environment. Just one single laundry load of polyester clothes could result in 700,000 microplastic fibers, they say. The energy costs to produce synthetic fiber has also been spotlighted by various environmental groups as a major source of greenhouse gas emissions.

Spider silk has previously been suggested as a possible natural replacement for these high-performance synthetic fibers. Not only is spider silk animal-derived, and therefore sidesteps these sustainability concerns, it also possesses extremely favorable physical properties.

Unfortunately, harvesting spider silk is a tough job – and not just if you are scared of spiders. Large-scale harvesting operations routinely fail because spiders are very territorial creatures, who also tend to become cannibalistic under these conditions.

But what if there was a usable way to harvest spider silk, sans cannibalism?

Modified silkworms produce bionic spider silk

Animal-derived silks are already produced commercially. But rather than coming from spiders, these silks are made by silkworms. So what if these animals could be nudged towards producing a more spider-like silk instead?

“Silkworm silk is presently the only animal silk fiber commercialized on a large scale, with well-established rearing techniques,” said Junpeng Mi, a PhD candidate at the College of Biological Science and Medical Engineering at Donghua University and the first author of the study. “Consequently, employing genetically modified silkworms to produce spider silk fiber enables low-cost, large-scale commercialization.”

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To get silkworms to produce spider silk, Mi and colleagues used CRISPR-Cas9 gene editing to add genes from Araneus ventricosus, an East Asian orb-weaving spider, that code for stronger silk proteins into silkworms while they were still in their eggs. Genes for more than 100 amino acids were needed for this, requiring hundreds of thousands of microinjections to accomplish.

After clearing this microinjection hurdle, which Mi says was “one of the most significant challenges” in the study, the researchers were keen to know whether their modifications had been successful. To verify this, they also added a gene that would make the silkworms’ eyes glow red under fluorescent light. To Mi’s delight, he saw little red eyes staring back at him when he looked at the hatched silkworms through a fluorescence microscope.

“I danced and practically ran to Professor Meng Qing’s office to share this result,” Mi recalled. “I remember that night vividly, as the excitement kept me awake.”

The researchers also performed what they call “localization” modifications on the transgenic spider silk proteins, to ensure that they would interact correctly with the proteins in the silkworm glands to form spinnable fibers. To guide this process, they also constructed a “minimal basic structure model” of silkworm silk.

The result was a cohort of genetically modified silkworms capable of spinning whole full-length spider silk fiber.

“This concept of ‘localization,’ introduced in this thesis, along with the proposed minimal structural model, represents a significant departure from previous research,” said Mi. “We are confident that large-scale commercialization is on the horizon.”

Towards new and improved “super materials”

To verify the usefulness of the bionic spider silk produced by these silkworms, the researchers tested the tensile strength and toughness of the fiber. Its extremely high tensile strength (1,299 Mpa) and toughness (319 MJ/m3) verify that the silkworm’s new silk is comparable to the properties of regular orb-weaving spider silk.

“Spider silk stands as a strategic resource in urgent need of exploration,” Mi said. “The exceptionally high mechanical performance of the fibers produced in this study holds significant promise in this field. This type of fiber can be utilized as surgical sutures, addressing a global demand exceeding 300 million procedures annually.”

Mi’s team believes that the commercial production of spider-like silk from genetically modified silkworms could also boost textile research for biomedical applications, aerospace technology, military capabilities and other smart materials.

In light of these successful experiments, Mi says that he plans to continue studying the use of these silkworms. Specifically, he wants to use the insights on the toughness and strength of this silk fiber to develop genetically modified silkworms that can produce spider silk fibers from both natural and engineered amino acids.

“The introduction of over one hundred engineered amino acids holds boundless potential for engineered spider silk fibers,” Mi said.

Reference: Mi J, Zhou Y, Ma S, et al. High-strength and ultra-tough whole spider silk fibers spun from transgenic silkworms. Matter. 2023. doi: 10.1016/j.matt.2023.08.013

This article is a rework of a press release issued by Cell Press. Material has been edited for length and content.