Bacteria that produce synthetic spider silk developed

Scientists have engineered a bacteria that produce a biosynthetic spider silk which mimics most of the natural counterpart's important traits, paving the way for many applications ranging from super thin surgical sutures to stronger fabrics.

The research, published in the journal Biomacromolecules, shows that the tensile strength and toughness of spider silk remains positively correlated with its molecular weight -- the bigger the molecule, the stronger the silk -- even in synthetic silk with a weight nearly twice that of the previous record-holder.

"People already knew about this correlation, but only with smaller-sized proteins. We found that even at this large size, there is still a very good correlation," said Fuzhong Zhang, associate professor at Washington University in the US.

Spider silk is among the strongest and toughest materials in the natural world, as strong as some steel alloys with a toughness even greater than bulletproof Kevlar.

Spider silk's unmatched combination of strength and toughness have made this protein-based material desirable for many applications.

Unfortunately, due to spiders' territorial and cannibalistic nature, their silk has been impossible to mass produce, so practical applications have yet to materialise.

One of the biggest challenges creating a biosynthetic spider silk has been creating a large enough protein. The challenge was so big, in fact, it required a whole new approach.

"We started with what others had done, making a genetically repeated sequence," said Christopher Bowen, a PhD student in Zhang's lab.

The DNA sequence was modelled after the sequence in spiders that is responsible for creating the silk protein. In theory, the more repetitions of the sequence, the bigger the resulting protein.

After the DNA sequence reaches a certain size, however, "the bacteria can't handle it, they chop the sequence into smaller pieces," Bowen said.

To get around this obstacle, researchers added a short genetic sequence to the silk DNA that promotes a chemical reaction between the resulting proteins, fusing them together to form an even bigger protein, bigger than has ever been produced and purified before.

"We made proteins basically twice as large as anyone's been able to make before," Bowen said.

They subsequently spun their exceptionally large biosynthetic silk proteins into fibres about a tenth the diameter of a human hair and tested their mechanical properties.

This biosynthetic silk is the first to replicate natural spider silk in terms of tensile strength, toughness, as well as other mechanical parameters such as elastic modulus and extensibility.

The team is now looking to work toward positioning biosynthetic silk fibres to replace some of the myriad of petroleum-based synthetic fibres used across industry.