Nav: Home

Bigger proteins, stronger threads: Synthetic spider silk

August 20, 2018

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 ranging from super thin surgical sutures to projectile resistant clothing. Unfortunately, due to spiders' territorial and cannibalistic nature, their silk has been impossible to mass produce, so practical applications have yet to materialize.

Scientists have been able to create some forms of synthetic spider silk, but have been unable to engineer a material that included most if not all of the natural silk's traits.

Until now.

Researchers in the School of Engineering & Applied Science at Washington University in St. Louis have engineered bacteria that produce a biosynthetic spider silk with performance on par with its natural counterparts in all of the important measures. And they've discovered something exciting about the possibilities ahead.

The new research, published Monday, Aug. 20 in Biomacromolecules, reveals 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 in the School of Engineering & Applied Science.

One of the biggest historical 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 modeled 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. It's a problem has been encountered many times in previous efforts. To get around this long-standing obstacle, Bowen and co-authors 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. Their silk protein chains are 556 kDa. Previously, the largest biosynthetic spider silk protein was 285 kDa. Even natural dragline silk proteins tend be around 370 kDa, although there are a few, bigger outliers.

Bowen and co-authors subsequently spun their exceptionally large biosynthetic silk proteins into fibers 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 (the maximum stress needed to break the fiber), toughness (the total energy absorbed by the fiber before breaking), as well as other mechanical parameters such as elastic modulus and extensibility.

Going forward, Zhang's lab is looking to work toward positioning biosynthetic silk fibers to replace some of the myriad of petroleum-based synthetic fibers used across industry.

"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," Zhang said.

And the Zhang group also plans to further explore the limits of their new approach. In addition to producing the first biosynthetic silk fibers to fully replicate the performance of natural spider silk, their work strongly suggests that the strength and toughness of these fibers will continue to increase if even larger proteins can be produced.
-end-
The School of Engineering & Applied Science at Washington University in St. Louis focuses intellectual efforts through a new convergence paradigm and builds on strengths, particularly as applied to medicine and health, energy and environment, entrepreneurship and security. With 96.5 tenured/tenure-track and 28 additional full-time faculty, 1,300 undergraduate students, 1,200 graduate students and 20,000 alumni, we are working to leverage our partnerships with academic and industry partners -- across disciplines and across the world -- to contribute to solving the greatest global challenges of the 21st century.

This work was supported by a Young Investigator Program from the Air Force Office of Scientific Research, grant no. FA95501510174 to FZ; an Early Career Faculty grant from NASA's Space Technology Research Grants Program, grant no. NNX15AU45G to FZ; and the National Institutes of Health, grant no. P41EB002520.

Washington University in St. Louis

Related Bacteria Articles:

Bacteria might help other bacteria to tolerate antibiotics better
A new paper by the Dynamical Systems Biology lab at UPF shows that the response by bacteria to antibiotics may depend on other species of bacteria they live with, in such a way that some bacteria may make others more tolerant to antibiotics.
Two-faced bacteria
The gut microbiome, which is a collection of numerous beneficial bacteria species, is key to our overall well-being and good health.
Microcensus in bacteria
Bacillus subtilis can determine proportions of different groups within a mixed population.
Right beneath the skin we all have the same bacteria
In the dermis skin layer, the same bacteria are found across age and gender.
Bacteria must be 'stressed out' to divide
Bacterial cell division is controlled by both enzymatic activity and mechanical forces, which work together to control its timing and location, a new study from EPFL finds.
How bees live with bacteria
More than 90 percent of all bee species are not organized in colonies, but fight their way through life alone.
The bacteria building your baby
Australian researchers have laid to rest a longstanding controversy: is the womb sterile?
Hopping bacteria
Scientists have long known that key models of bacterial movement in real-world conditions are flawed.
Bacteria uses viral weapon against other bacteria
Bacterial cells use both a virus -- traditionally thought to be an enemy -- and a prehistoric viral protein to kill other bacteria that competes with it for food according to an international team of researchers who believe this has potential implications for future infectious disease treatment.
Drug diversity in bacteria
Bacteria produce a cocktail of various bioactive natural products in order to survive in hostile environments with competing (micro)organisms.
More Bacteria News and Bacteria Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Listen Again: Reinvention
Change is hard, but it's also an opportunity to discover and reimagine what you thought you knew. From our economy, to music, to even ourselves–this hour TED speakers explore the power of reinvention. Guests include OK Go lead singer Damian Kulash Jr., former college gymnastics coach Valorie Kondos Field, Stockton Mayor Michael Tubbs, and entrepreneur Nick Hanauer.
Now Playing: Science for the People

#562 Superbug to Bedside
By now we're all good and scared about antibiotic resistance, one of the many things coming to get us all. But there's good news, sort of. News antibiotics are coming out! How do they get tested? What does that kind of a trial look like and how does it happen? Host Bethany Brookeshire talks with Matt McCarthy, author of "Superbugs: The Race to Stop an Epidemic", about the ins and outs of testing a new antibiotic in the hospital.
Now Playing: Radiolab

Dispatch 6: Strange Times
Covid has disrupted the most basic routines of our days and nights. But in the middle of a conversation about how to fight the virus, we find a place impervious to the stalled plans and frenetic demands of the outside world. It's a very different kind of front line, where urgent work means moving slow, and time is marked out in tiny pre-planned steps. Then, on a walk through the woods, we consider how the tempo of our lives affects our minds and discover how the beats of biology shape our bodies. This episode was produced with help from Molly Webster and Tracie Hunte. Support Radiolab today at Radiolab.org/donate.