Bacteria build stronger biosynthetic spider silk, protein by protein
Strong as steel and tougher than Kevlar, spider silk is one of nature's most impressive materials, but try as we might, we just haven't been able to harness it for our own use on a practical scale. Most synthetic versions aren't completely up to scratch, but researchers from Washington University in St. Louis have now engineered bacteria to produce biosynthetic spider silk that they say performs as well as the real stuff.
Farming spiders might seem like the obvious way to get spider silk, but the arachnids just aren't productive enough to make that viable. Synthetic versions have been spun in the past by splicing silk-producing genes from spiders into worms, goats and bacteria, but these have had issues matching nature's wonder material.
For the new study, the researchers have gone down the bacteria route, but on the way they've tried to make the silk stronger on a molecular level. The key, the team says, is in the proteins that fuse together to form the strands. This process is driven by a particular repeating sequence of DNA, and the more times that sequence repeats, the bigger the protein and the stronger the resulting silk turns out.
Sounds like a simple recipe, but the first hurdle the team had to overcome was the fact that the bacteria can't handle sequences that get too big and chop them into smaller pieces. To deal with that, the researchers added a new short sequence to the silk DNA. This triggers a chemical reaction between proteins, allowing them to fuse together to create a larger protein.
The silk protein chains created by the team measure 556 kiloDaltons (kDa, an atomic unit of measurement). That's longer than natural silk proteins that usually measure 370 kDa, and almost twice as long as other biosynthetic spider silk proteins that max out around 285 kDa.
To test the material, the team then spun these larger proteins into fibers that measured about one-tenth the diameter of a human hair. The researchers report that the material was able to match natural spider silk in terms of tensile strength, toughness, extensibility and resistance to deformation.
The researchers say that the study suggests that the key to making stronger silk fibers is figuring out how to make even larger proteins. Along with that goal, the team plans to investigate how to produce their silk on practical scales.
"We will continue to work on making the process more scalable and economical by making it easier to handle, reducing the amount of chemicals needed, and increasing the robustness and efficiency," says Fuzhong Zhang, an author of the study.
The research was published in the journal Biomacromolecules.