Spider silk is one of the strongest and most resistant materials known in nature. 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.
The artificial silk was actually produced by the bacteria, and not the researchers. The bacteria 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.
Previously, Zhang and his lab engineered bacteria that produced an artificial spider silk which performed equally with its natural counterparts in most 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 changed the amino acid sequence of spider silk proteins to introduce new properties, while some of the attractive features of spider silk remained. One of the challenges when producing recombinant spider silk fiber is the need to create β-nanocrystals, a key factor 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.”
The researchers modified the silk sequence by introducing amyloid sequences with a high tendency to form β-nanocrystals. The resulting proteins had less repetitive amino acid sequences than spider silk, making them easier to be produced by engineered bacteria. The bacteria made a hybrid polymeric amyloid protein with 128 repeating units, which makes the fiber stronger and tougher.
The proteins resulted in a fiber with gigapascal strength, which is stronger than common steel. Its strength and toughness are even higher than some reported natural spider silk fibers.
The study explored three sequences, but thousands of different amyloid sequences could 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.”
