A new fiber, made by genetically engineered bacteria, is stronger than steel and tougher than Kevlar.
From: Washington University in Saint
Louis
July
20, 2021 -- Spider silk is said to be one of the strongest, toughest materials
on the Earth. Now engineers at Washington University in St. Louis have designed
amyloid silk hybrid proteins and produced them in engineered bacteria. The
resulting fibers are stronger and tougher than some natural spider silks.
Their research was published in the
journal ACS Nano.
To be precise, the artificial silk --
dubbed "polymeric amyloid" fiber -- was not technically produced by
researchers, but by bacteria that were genetically engineered in the lab of
Fuzhong Zhang, a professor in the Department of Energy, Environmental & Chemical
Engineering in the McKelvey School of Engineering.
Zhang has worked with spider silk
before. In 2018, his lab engineered bacteria that produced a recombinant spider
silk with performance on par with its natural counterparts in all of the
important mechanical properties.
"After our previous work, I
wondered if we could create something better than spider silk using our
synthetic biology platform," Zhang said.
The research team, which includes first
author Jingyao Li, a PhD student in Zhang's lab, modified the amino acid
sequence of spider silk proteins to introduce new properties, while keeping
some of the attractive features of spider silk.
A problem associated with recombinant
spider silk fiber -- without significant modification from natural spider silk
sequence -- is the need to create β-nanocrystals, a main component of natural
spider silk, which contributes to its strength. "Spiders have figured out
how to spin fibers with a desirable amount of nanocrystals," Zhang said.
"But when humans use artificial spinning processes, the amount of
nanocrystals in a synthetic silk fiber is often lower than its natural
counterpart."
To solve this problem, the team
redesigned the silk sequence by introducing amyloid sequences that have high
tendency to form β-nanocrystals. They created different polymeric amyloid
proteins using three well-studied amyloid sequences as representatives. The
resulting proteins had less repetitive amino acid sequences than spider silk,
making them easier to be produced by engineered bacteria. Ultimately, the
bacteria produced a hybrid polymeric amyloid protein with 128 repeating units.
Recombinant expression of spider silk protein with similar repeating units has
proven to be difficult.
The longer the protein, the stronger and
tougher the resulting fiber. The 128-repeat proteins resulted in a fiber with
gigapascal strength (a measure of how much force is needed to break a fiber of
fixed diameter), which is stronger than common steel. The fibers' toughness (a
measure of how much energy is needed to break a fiber) is higher than Kevlar
and all previous recombinant silk fibers. Its strength and toughness are even
higher than some reported natural spider silk fibers.
In collaboration with Young- Shin Jun,
professor in the Department of Energy, Environmental & Chemical
Engineering, and her PhD student Yaguang Zhu, the team confirmed that the high
mechanical properties of the polymeric amyloid fibers indeed come from the
enhanced amount of β-nanocrystals.
These new proteins and the resulting fibers
are not the end of the story for high-performance synthetic fibers in the Zhang
lab. They are just getting started. "This demonstrates that we can
engineer biology to produce materials that beat the best material in
nature," Zhang said.
This work explored just three of
thousands of different amyloid sequences that could potentially enhance the
properties of natural spider silk. "There seem to be unlimited
possibilities in engineering high-performance materials using our
platform," Li said. "It's likely that you can use other sequences,
put them into our design and also get a performance-enhanced fiber."
https://www.sciencedaily.com/releases/2021/07/210720185821.htm
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