Engineered E. coli spin fibers 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 silkMovie Camera 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.

After the bacteria produced the protein, the researchers allowed the silk to self-assemble in a bath of water and alcohol before stretching the fibers to six times their original length. This process of “wet spinning” mimics a spider drawing the silk out of its body with its hind legs, which improves the alignment of the proteins as well as the fiber’s toughness. The researchers found the recombinant fibers were more elastic but weaker than real silk. However, because toughness is a combination of elasticity and strength, the artificial fibers were deemed as tough as the natural product.

Using a self-assembly of recombinant spidroins, biomimetic spinning dopes are produced and wet-spun into fibers. Upon varying the molecular design of the underlying recombinant spidroins, the influence of the amino- and carboxy-terminal domains, as well as the size of the repetitive core domain on fiber mechanics, is determined. Fiber toughness upon biomimetic processing equals and even slightly exceeds that of natural ones.

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.

6 pages of supplemental material

SOURCES – Advanced Materials, New Scientist

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