Engineered fibres are stronger than steel and spider silk
Image credit: Washington University in St. Louis/Jingyao Li
Researchers at Washington University in St. Louis have developed a microbially produced fibre which has gigapascal strength, outperforming steel, Kevlar, and some spider silks.
Spider silk is recognised as one of the strongest, toughest materials on Earth. Now, engineers at Washington University have developed fibres stronger and tougher than some natural spider silks which are produced by engineered bacteria.
The amyloid-silk hybrid proteins were developed in the laboratory of Professor Fuzhong Zhang, who has worked extensively with spider silk. In 2018, his lab engineered bacteria to produce a recombinant spider silk on par with its natural counterparts regarding all important mechanical properties.
“After our previous work, I wondered if we could create something better than spider silk using our synthetic biology platform,” said Zhang.
Zhang and his team modified the amino acid sequence of spider silk proteins to introduce new properties, while maintaining the most attractive features of spider silk.
A problem associated with recombinant spider silk fibre is the need to create β-nanocrystals, a critical component of natural spider silk which contributes to its incredible strength. Zhang explained: “Spiders have figured out how to spin fibres with a desirable amount of nanocrystals. But when humans use artificial spinning processes, the amount of nanocrystals in a synthetic silk fibre 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 fewer repetitive amino acid sequences than spider silk, thus making them easier for the engineered bacteria to produce. Ultimately, the bacteria produced a hybrid polymeric amyloid protein with 128 repeating units; production of artificial spider silk protein with similar repeating units has been a challenge.
The longer the protein, the stronger and tougher the fibre. The 128-repeat proteins resulted in fibre with gigapascal strength – stronger than common steel – while its toughness (a measure of how much energy is needed to break a fibre) is higher than Kevlar and all previous artificial silk fibres. Its strength and toughness are even higher than some natural spider silks.
Zhang collaborated with chemical engineers to confirm that the impressive mechanical properties of the fibre came from the enhanced quantity of β-nanocrystals.
Having demonstrated that it is possible to engineer bacteria to produce superlative materials, Zhang and his colleagues hope to develop more high-performance fibres. This project explored just three of thousands of possible amyloid sequences that could enhance spider silk properties.
Jingyao Li, a PhD candidate who worked on the project, explained: “There seem to be unlimited possibilities in engineering high-performance materials using our platform. It's likely that you can use other sequences, put them into our design and also get a performance-enhanced fibre.”
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