Bacteria are helping to make engineered silk that rivals the strength and stretchiness of a spider’s stiff dragline silk, the type from which the arachnids dangle.
Pound for pound, dragline silk is stronger and tougher than steel. Engineers have tried for decades to create a synthetic mimic from genetically modified bacteria, yeast and even goat milk, but have always fallen short.
Part of the challenge is that the genetic information for dragline silk is a long string of repeating DNA. And those previously tested organisms’ cell machinery haphazardly alters or chops up such series.
To overcome this issue, researchers precisely separated the repeating DNA into bits and inserted each repeating piece into an E. coli microbe. These smaller pieces were less likely to be further altered within the bacteria, and each microbe then followed the genetic instructions to produce a short strand of silk. The researchers added to the end of each strand a chemical tag that glued the individual fibers together.
The resulting material behaved like dragline silk. Its tensile strength, or resistance to being pulled apart, was measured at 1.03 gigapascals, about the same as for naturally produced dragline silk. The engineered silk’s toughness measured 114 megajoules per cubic meter, compared with around 100 megajoules for silk made by spiders. And the engineered silk strands could stretch 18 percent before breaking, the same as natural dragline silk.
“We can now use bacteria to produce something as good as nature,” says synthetic biologist Fuzhong Zhang of Washington University in St. Louis who presented the research April 2 at the American Chemical Society’s annual meeting in Orlando, Fla.
The new silk was developed in part with NASA funding for applications such as giving astronauts a means of creating tough materials while on Mars. But the substance could be used in designing stronger materials for medical or textile applications, Zhang says, such as impact-resistant fabrics or surgical sutures.
The team is working to scale up the process by engineering bacteria able to produce full silk strands rather than just segments.