Modified E. coli spin fibres as tough as spider silk

Spider silk is stronger than steel and tougher than Kevlar, but efforts to spin our own have so far failed to match the real thing. Now a German research group has come up with artificial fibres that equal its toughness, which could lead to safer airbags.

Previous attempts to mimic spider silk have focused on two molecules that provide its material properties. One creates a tough, crystalline material, and the other builds a more gel-like substance. The crystal is suspended in the gel to form a large protein.

But Thomas Scheibel at the University of Bayreuth in Germany and his colleagues realised that this neglected two smaller molecules that help align the strands.

"They do not contribute to the final structure and performance," he says, which is why they had been left out. "But we found out they are actually important in getting the molecules aligned."

His team spliced spider genes into E. coli, which enabled the bacteria to produce all four molecules in a bath of alcohol and water. The team then used a method called wet spinning to draw out the fibres, creating the artificial silk.

Stretch it out

The fibres were toughest when the team stretched them just after they formed, much like a spider pulls out webbing with its hind legs, to elongate and align the molecules.

The resulting material is not as strong as real spider silk, but is more elastic, meaning it can't take as much force without breaking but can stretch further. Toughness, a measure of how much energy a material can absorb per unit volume, is determined by both of these properties, which is why the artificial silk is as tough as the real thing.

That's not surprising, says Scheibel, because real spider silk is made of three proteins with different properties, and his team only used the set of genes for the most elastic protein. They are now working on a more advanced version of the artificial silk that uses all three, to better match the real properties.

In the meantime, the current fibre's toughness could be put to good use in making car airbags. "An airbag should have exactly the properties that a spider web has," says Scheibel – strong and elastic. Current airbags, made from materials like Kevlar, are strong but not elastic, so they can reflect energy from a crash back into the driver and cause injuries. The artificial silk could solve this, provided the team can scale up production, which might be difficult, says Scheibel.

Journal reference: Advanced Materials, DOI: 10.1002/adma.201404234

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