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Stronger Than Steel, Tougher Than Kevlar

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A high molecular weight amyloid fiber containing a protein that is repeated 128 times. Credit: Jingyao Li

The artificially designed amyloid-silk hybrid protein developed at Zhang Labs is superior to some spider silks.

Spider silk is said to be one of the strongest and toughest materials on the planet. Currently, engineers at Washington University in St. Louis are designing amyloid silk hybrid proteins and producing them with artificial bacteria. The resulting fiber is stronger and tougher than some natural spider silk.

Their study was published in the journal ACS Nano..

Spinning polymer amyloid fiber

The 128-repeat protein resulted in fibers with stronger gigapascal strength than ordinary steel. The toughness of the fiber is higher than that of Kevlar and all previous recombinant silk fibers. Its strength and toughness are even higher than some reported natural spider silk fibers.Credits: University of Washington, St. Louis / Jin Yaori

To be precise, artificial silks called “polymeric amyloid” fibers are not technically manufactured by researchers, but by genetically engineered bacteria in the laboratory of Fuzhong Zhang, a professor of the Department of Energy and Environmental Chemistry. I did. McKelby Faculty of Engineering.

Zhang has dealt with spider silk before. In 2018, his lab designed a bacterium that produces recombinant spider silk with performance comparable to its natural counterpart in all of its important mechanical properties.

“After previous work, I wondered if I could use a synthetic biology platform to create something better than Spider Silk,” Zhang said.

A research team, including lead author JingyaoLi, a PhD student in Zhang’s lab, has modified the amino acid sequence of spider silk proteins to introduce new properties while retaining some of the fascinating features of spider silk. Did.

The problem with recombinant spider silk fibers is the need to create β-nanocrystals, which are the main components of natural spider silk, without significantly changing the arrangement of natural spider silk. “Spider has come up with a way to spin fibers with the desired amount of nanocrystals,” Zhang said. “But when humans use artificial spinning processes, the amount of nanocrystals in synthetic silk fibers is often less than that of natural ones.”

To solve this problem, the team redesigned the silk sequence by introducing an amyloid sequence that is more likely to form β-nanocrystals. They used three well-studied amyloid sequences as representatives to create a variety of high molecular weight amyloid proteins. The resulting protein has fewer repetitive amino acid sequences than spider silk and is more susceptible to production by engineered bacteria. Ultimately, the bacterium produced a hybrid polymeric amyloid protein with 128 repeating units. Recombinant expression of spider silk proteins with similar repeating units has proven difficult.

Toughness and strength of various fibers

This chart compares the toughness and strength of various natural and recombinant silk fibers. Shown in red are high molecular weight amyloid fibers developed in Fuzhong Zhang’s laboratory.Credits: University of Washington, St. Louis / Jin Yaori

The longer the protein, the stronger and stronger the resulting fiber. The 128-fold repeating protein yielded fibers of gigapascal strength (a measure of the force required to break fixed-diameter fibers). It is stronger than ordinary steel. The toughness of the fiber (a measure of the amount of energy required to break the fiber) is higher than that of Kevlar and all previous recombinant silk fibers. Its strength and toughness are even higher than some reported natural spider silk fibers.

The team, in collaboration with Professor Yong Shin-jun of the Department of Energy and Environmental Chemistry and PhD student Yaguang Zhu, confirms that the high mechanical properties of high molecular weight amyloid fibers actually derive from the increased amount of β-nanocrystals. Did. ..

These new proteins and the resulting fibers are not the end of the story of Zhang Institute’s high-performance synthetic fibers. They are just getting started. “This shows that we can design biology to produce materials that beat the best materials in nature,” Zhang said.

This work investigated thousands of different amyloid sequences that could potentially enhance the properties of natural spider silk. “There seems to be endless possibilities in designing high-performance materials using our platform,” says Li. “You may be able to use other sequences to incorporate them into your design and obtain fibers with improved performance.”

Reference: “Microbial synthetic polymer amyloid fibrils promote β-nanocrystal formation and show gigapascal tensile strength”, Jingyao Li, Yaguang Zhu, Han Yu, Bin Dai, Young-Shin Jun, Fuzhong Zhang, 2021 7 12th of March ACS Nano..
DOI: 10.1021 / acsnano.1c02944

This study was published by the US Department of Agriculture, No. 20196702129943, and Navy Research Bureau, No. Supported by N000141912126.



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