Researchers have seriously considered the imaginary scenarios depicted in Spider-Man and created an innovative web-slinging technology. This new technology allows a fluid material to be ejected from a needle, solidifying instantly into a strong string that can both stick to and lift objects.
Every child who has delved into a comic book or seen a Spider-Man film has fantasized about shooting webs from their wrists, soaring over city blocks, and capturing villains. At Tufts University, researchers have taken those dreams seriously, developing the first web-slinging technology that enables a fluid to shoot from a needle, rapidly solidifying into a string capable of lifting and sticking to various objects.
The adhesive fibers were developed at the Tufts University Silklab using silk harvested from silk moth cocoons. These cocoons are boiled in a solution that breaks down into proteins known as fibroin. By using narrow bore needles, the silk fibroin solution can be extruded, forming a stream that solidifies into fibers upon contact with air when specific additives are introduced.
Nature served as the initial source of inspiration for creating silk fibers used in tethers, webs, and cocoons. Various creatures, including spiders, ants, wasps, bees, butterflies, moths, beetles, and even flies, can produce silk at different life stages. The Silklab also draws inspiration from nature to pioneer innovative uses for silk fibroin, including the development of powerful glues that function underwater, printable sensors applicable on nearly any surface, edible coatings that prolong the freshness of fruits and vegetables, a material that enhances solar cell efficiency, and more environmentally friendly methods for microchip production.
Despite notable advancements with silk-based materials, the researchers faced difficulties in imitating the exceptional skills of spiders, which manipulate stiffness, elasticity, and stickiness in the threads they produce.
A significant breakthrough occurred unexpectedly. Marco Lo Presti, a research assistant professor at Tufts, recounted, “While I was working on creating extremely strong adhesives using silk fibroin, I noticed a web-like substance forming at the bottom of my glass while cleaning my lab equipment with acetone.”
This accidental finding addressed several engineering hurdles related to mimicking spider threads. When exposed to organic solvents like ethanol or acetone, silk fibroin solutions can gradually transform into a semi-solid hydrogel over several hours. However, the introduction of dopamine, used in crafting the adhesives, enabled the solidification process to happen almost instantaneously. By quickly mixing the organic solvent, the silk solution rapidly formed strong, sticky fibers. The chemistry of dopamine and its polymers resembles that utilized by barnacles to create their strongly adhering fibers.
The subsequent step involved spinning the fibers in air. By adding dopamine to the silk fibroin solution, it appeared to hasten the shift from liquid to solid by removing water from the silk. When injected through a coaxial needle, a fine stream of the silk solution was enveloped in a layer of acetone that triggered solidification. The acetone evaporated mid-air, leaving a fiber that could adhere to any surfaces it encountered. To further improve their capabilities, the researchers enhanced the silk fibroin-dopamine mixture with chitosan, a by-product of insect exoskeletons that increased the fibers’ tensile strength by up to 200 times, and borate buffer, which improved their adhesiveness roughly 18-fold.
The fibers can be engineered to have diameters that range from human hair thickness to about half a millimeter, depending on the needle bore used.
The device can generate fibers capable of lifting objects more than 80 times their own weight across diverse conditions. The research team demonstrated this ability by picking up a cocoon, a steel bolt, a lab tube floating on water, a scalpel partially buried in sand, and a wood block from a distance of around 12 centimeters.
Lo Presti explained, “If you observe nature, you’ll find that spiders do not shoot their webs. They typically produce silk from their glands, make contact with a surface, and then draw out lines to construct their webs. We are showcasing a method to shoot a fiber from a device, which can then cling to and lift an object from a distance. This work doesn’t just represent bio-inspired material; it’s truly material inspired by superheroes.”
While natural spider silk continues to be about 1000 times stronger than the fibers produced in this study, with some creativity and engineering, advancements will keep emerging, opening doors to numerous technological possibilities.
“As scientists and engineers, we explore the space between imagination and reality. That’s where real innovation happens,” stated Fiorenzo Omenetto, Frank C. Doble Professor of Engineering at Tufts University and head of the Silklab. “Nature and even comics and science fiction inspire us. Here, our aim was to redesign our silk material to function like how nature intended it, along with the dreams imagined by comic book creators.”
