Spider silk: The toughest material on this planet

Debarati Basu, Makaut WB

Genetically engineered bacteria produce a new fiber known as spider silk which is stronger than normal silk and tougher than Kevlar.

Spider silk is considered to be the toughest material on this planet. According to the research work published in the journal ACS Nano, engineers at Washington University in St. Louis have used genetically engineered bacteria to outline amyloid silk hybrid protein and in turn, produce them in these bacteria. The produced fiber which is silk fiber is tougher than many of the spider silks.

What is Spider silk?

Spider silk is artificial silk that was rendered by genetically modified bacteria in the lab of Fuzhong Zhang, a professor in the Department of Energy, Environmental & Chemical Engineering in the McKelvey School of Engineering. The artificial silk label “polymeric amyloid” and the silk produced is one of the toughest materials than other fibers.

Professor Zhang had worked with spider silk previously in 2018 in his lab. He had genetically modified bacteria by splicing silk-producing genes into the bacteria thus producing a recombinant fiber that is at par with the artificial spider silk.

Zhang stated that they wanted to engineer something better than spider silk by utilizing synthetic biology platform. Zhang’s research team also consists of Jingyao Li, a Ph.D. student in Zhang’s lab who further redesigned the amino acid sequence of spider silks to acquaint new properties while maintaining some of the features of spider silk.

Features of Spider silk:

The main component of spider silk is β-nanocrystals which are microscopic particles that contribute to its increased strength and durability. Thus spider silk is tougher than other fibers. Zhang said spiders know how to spin fibers by using a desirable amount of nanocrystals. In the case of humans, they use artificial spinning processes and the amount of nanocrystals is comparatively lower in a synthetic silk fiber than the natural silk fibers.

One of the problems associated with such genetically modified silk fibers is how to create β-nanocrystals. The team solved this problem by redesigning the silk sequence by introducing amyloid sequences which tend to form β-nanocrystals.

Significance of the genetically modified silk:

The team further develop different polymeric amyloid proteins. The resulting proteins consist of less repetitive amino acid sequences as compared to spider silk. Thus they can be easily produced by genetically modified bacteria. A hybrid of polymeric amyloid protein with 128 repeating units is generated by genetically engineered bacteria. The greater the length of the proteins the stronger and tougher the resulting fiber. The 128-repeating proteins emerge in fiber with gigapascal strength which is usually stronger than steel. The gigapascal strength is a measure that determines the amount of force required to break a fiber of fixed diameter. The toughness of fiber is a measure of the amount of energy required to break a fiber. The fibers’ toughness is greater than all recombinant silk fibers as well as that of Kevlar.

The team further stated that the polymeric amyloid fibers’ mechanical properties are obtained from the enhanced amount of β-nanocrystals.

The beginning story for high-performance synthetic fibers in the Zhang lab is the resulting fibers and the new proteins. Zhang said that biology can be engineered for the production of materials that can be the better version of their natural counterparts. Li stated that they have innumerable possibilities to produce high-performance materials. He further said that they will use other sequences in their design to get better-performing fiber.

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References: Li, J., Zhu, Y., Yu, H., Dai, B., Jun, Y.-S., & Zhang, F. (2021). Microbially synthesized polymeric amyloid fiber promotes the β-nanocrystal formation and displays gigapascal tensile strength. ACS Nano, acsnano.1c02944. https://doi.org/10.1021/acsnano.1c–02944

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