It’s possible that I shall make an ass of myself. But in that case one can always get out of it with a little dialectic. I have, of course, so worded my proposition as to be right either way (K.Marx, Letter to F.Engels on the Indian Mutiny)
Friday, March 07, 2025
ARACHNOLOGY
Stretching spider silk makes it stronger
New study finds the amount of stretching determines the fibers’ properties
Scanning electron microscopy images of fibers from engineered spider silk. To validate their computational findings, the Northwestern team used spectroscopy techniques to examine how the protein chains stretched and aligned in real fibers from engineered spider silk.
When spiders spin their webs, they use their hind legs to pull silk threads from their spinnerets. This pulling action doesn’t just help the spider release the silk, it’s also a crucial step in strengthening the silk fibers for a more durable web.
In a new study, Northwestern University researchers have discovered why the role of stretching is so important. By simulating spider silk in a computational model, the team discovered the stretching process aligns the protein chains within the fibers and increases the number of bonds between those chains. Both factors lead to stronger, tougher fibers.
The team then validated these computational predictions through laboratory experiments using engineered spider silk. These insights could help researchers design engineered silk-inspired proteins and spinning processes for various applications, including strong, biodegradable sutures and tough, high-performance, blast-proof body armor.
The study will be published on Friday (March 7) in the journal Science Advances.
“Researchers already knew this stretching, or drawing, is necessary for making really strong fibers,” said Northwestern’s Sinan Keten, the study’s senior author. “But no one necessarily knew why. With our computational method, we were able to probe what’s happening at the nanoscale to gain insights that cannot be seen experimentally. We could examine how drawing relates to the silk’s mechanical properties.”
“Spiders perform the drawing process naturally,” said Northwestern Jacob Graham, the study’s first author. “When they spin silk out of their silk gland, spiders use their hind legs to grab the fiber and pull it out. That stretches the fiber as it’s being formed. It makes the fiber very strong and very elastic. We found that you can modify the fiber’s mechanical properties simply through modifying the amount of stretching.”
An expert in bioinspired materials, Keten is the Jerome B. Cohen Professor of Engineering, professor and associate chair of mechanical engineering and professor of civil and environmental engineering at Northwestern’s McCormick School of Engineering. Graham is a Ph.D. student in Keten’s research group.
Stronger than steel, tougher than Kevlar
Researchers long have been interested in spider silk because of its remarkable properties. It’s stronger than steel, tougher than Kevlar and stretchy like rubber. But farming spiders for their natural silk is expensive, energy-intensive and difficult. So, scientists instead want to recreate silk-like materials in the lab.
“Spider silk is the strongest organic fiber,” Graham said. “It also has the advantage of being biodegradable. So, it’s an ideal material for medical applications. It could be used for surgical sutures and adhesive gels for wound-closure because it would naturally, harmlessly degrade in the body.”
Study coauthor Fuzhong Zhang, the Francis F. Ahmann Professor at Washington University (WashU) in St. Louis, has been engineering microbes to produce spider-silk materials for several years. By extruding engineered spider silk proteins and then stretching them by hand, the team has developed artificial fibers similar to threads from the golden silk orb weaver, a large spider with a spectacularly strong web.
Simulating stretchiness
Despite developing this “recipe” for spider silk, researchers still don’t fully understand how the spinning process changes fiber structure and strength. To tackle this open-ended question, Keten and Graham developed a computational model to simulate the molecular dynamics within Zhang’s artificial silk.
Through these simulations, the Northwestern team explored how stretching effects the proteins’ arrangement within the fibers. Specifically, they looked at how stretching changes the order of proteins, the connection of proteins to one another and the movement of molecules within the fibers.
Keten and Graham found that stretching caused the proteins to “line up,” which increased the fiber’s overall strength. They also found that stretching increased the number of hydrogen bonds, which act like bridges between the protein chains to make up the fiber. The increase in hydrogen bonds contributes to the fiber’s overall strength, toughness and elasticity, the researchers found.
“Once a fiber is extruded, its mechanical properties are actually quite weak,” Graham said. “But when it’s stretch up to six times its initial length, it becomes very strong.”
Experimental validation
To validate their computational findings, the team used spectroscopy techniques to examine how the protein chains stretched and aligned in real fibers from the WashU team. They also used tensile testing to see how much stretching the fibers could tolerate before breaking. The experimental results agreed with the simulation’s predictions.
“If you don’t stretch the material, you have these spherical globs of proteins,” Graham said. “But stretching turns these globs into more of an interconnected network. The protein chains stack on top of one another, and the network becomes more and more interconnected. Bundled proteins have more potential to unravel and extend further before the fiber breaks, but initially extended proteins make for less extensible fibers that require more force to break.”
Although Graham used to think spiders were just creepy-crawlies, he now sees their potential to help solve real problems. He notes that engineered spider silk provides a stronger, biodegradable alternative to other synthetic materials, which are mostly petroleum-derived plastics.
“I definitely look at spiders in a new light,” Graham said. “I used to think they were nuisances. Now, I see them as a source of fascination.”
The study, “Charting the envelope of mechanical properties of synthetic silk fibers through predictive modeling of the drawing process,” was supported by the National Science Foundation (grant numbers OIA-2219142 and DMR-2207879).
Natural spider kiting silk, released fibre by fibre after being used up by spiders, spontaneously forms uniform surfaces between tree branches, inspiring our technological discovery. Additional video or photographic material is kindly provided by the Authors on request.
Credit: Those included in the manuscript are covered by by-nc-nd/4.0/ licence. Credit: All Authors' work.
Can robots be predesigned for unpredictability?
While today’s large language models adapt situationally on the fly, their bodies remain fixed. They are either optimized for a specific task or built into a one-size-fits-all principle that rarely excels. But what if a machine could develop any structure demanded by its situatedness, right when and where it’s needed?
Researchers at Tartu University’s Institute of Technology have unveiled a robotics concept that redefines adaptability by literally weaving its body on demand, much like spiders spin their webs. By extruding a heated polymer solution that cools into fine fibers, the robot creates custom components in situ. The result is a dynamic melding of machine and environment! A seamless transition that bypasses the rigid separation of traditional robotic design.
In a series of experiments, the team showcased the robot’s remarkable ability to operate in complex environments. In one demonstration, the machine spun a continuous, flexible fiber network across a simulated debris field, building its own bridge over obstacles indifferently whether the path was lined with razor-sharp glass shards or soft bird feathers. In another test, the robot spun itself a fibrous “limb” to gently retrieve a fragile flower, illustrating a level of dexterity that predesigned embodiments cannot match.
The team demonstrated indiscriminate adhesion and anchoring of in-situ spun webs on virtually any substrate, regardless of shape, material, or state of aggregation. Much like spiderwebs, the synthetic web leveraged both physical adhesion and mechanical entanglement to secure itself to a broad range of supports.
In experiments, the web successfully anchored on challenging surfaces such as Teflon, a sponge saturated with mineral oil, and a waxy plant leaf.
“Our approach takes a cue from spiders as nature’s ingenious engineers, yet we found a loophole that lets us sidestep the limitations and excessive complexity of directly imitating spiders,” said Marie Vihmar, lead author of the study published in npj Robotics.
With a background in design studies, Vihmar brings a fresh perspective on non-anthropocentric design and how the form and shape of materials create functionality, while the senior author Indrek Must, who is trained in material science, ensures the technological robustness of the innovation.
This interdisciplinary collaboration converges design thinking, material science, and robotics, yielding insights and solutions that remain elusive to conventional approaches within any single discipline.
By exploiting the self-assembling properties of polymer fibers, also observed in cast-off kiting silk of spiders in nature, the team has created a system that dynamically assembles itself to meet the immediate challenges of unpredictable environments. This not only broadens the scope of robotics in disaster relief but also rethinks how machines interact with the world.
This contribution paves the way for robots that don’t simply adapt to their surroundings, but actively transform them! From search-and-rescue operations in disaster zones to adaptive construction methods that seamlessly merge machines with landscapes, the technology challenges conventional industrial thinking. Instead of forcing the environment to accommodate rigid, predesigned systems, this innovative “forest thinking” approach empowers machines to grow and evolve on the spot.
Supported by the Estonian Research Council, this research marks a significant step forward in the convergence of biological inspiration and robotics. Introducing an era where machines are not static tools, but dynamic entities capable of reinventing themselves not only mentally, but also physically.
No comments:
Post a Comment