Web-slinging technology inspired by Spider-Man is now a reality thanks to innovative work by researchers at Tufts University.
This remarkable advancement uses silk-based materials to shoot a fluid through a fine needle, where it instantly solidifies into a strong, sticky string.
The string is capable of adhering to surfaces and lifting objects with surprising strength and precision.
Wonders of web-slinging technology
The web-slinging technology involves the creation of sticky fibers sourced from silk moth cocoons.
The cocoons, found within the Silklab of Tufts University, are processed in a solution until they break down into fibroin – the base proteins of the silk.
Once extruded through fine bore needles, the silk fibroin solution transforms into a stream. Add the right ingredients, and this stream becomes a string the moment it hits open air.
The natural marvel of silk
Nature has always been a primary source of inspiration for the creation and utilization of silk fibers. Several creatures, from spiders and ants to butterflies and beetles, produce silk at some stage in their life cycle.
The Silklab at Tufts University has been inspired by this natural marvel, leading to a series of remarkable developments.
The researchers have created strong adhesives that function underwater, printable sensors, edible coatings to increase the life of produce, and eco-friendly microchip manufacturing methods.
Inspiration strikes unexpectedly
Despite their progress with silk-based materials, the researchers faced challenges in emulating the prowess of spiders, precisely controlling the stiffness, elasticity, and adhesive properties of the spun threads. However, a revelation arrived through a serendipitous event.
“I was working on a project making extremely strong adhesives using silk fibroin, and while I was cleaning my glassware with acetone, I noticed a web-like material forming on the bottom of the glass,” said Marco Lo Presti, research assistant professor at Tufts.
This accidental discovery facilitated the overcoming of several engineering hurdles in replicating spider threads.
The magic of chemistry
The researchers realized that silk fibroin solutions could form a semi-solid hydrogel over several hours when exposed to organic solvents like ethanol or acetone.
The addition of dopamine, an element used in making adhesives, allowed the solidification process to occur almost instantly.
The composition featuring dopamine and its polymers is similar to the chemistry that barnacles use to create fibers that adhere tenaciously to surfaces.
In order to spin these fibers in the air, the researchers added dopamine to the silk fibroin solution. In the presence of dopamine, the transition from liquid to solid was accelerated by drawing water away from the silk.
When launched through a coaxial needle, a thin stream of the silk solution gets enveloped by a layer of acetone, triggering the solidification.
Real-life web-slinging technology
The acetone evaporates mid-air, leaving behind a fiber attached to any object it comes in contact with.
The researchers bolstered the silk fibroin-dopamine solution with chitosan, a derivative of insect exoskeletons, and borate buffer, which increased the adhesiveness and tensile strength of the fibers significantly.
The device can shoot fibers capable of lifting objects over 80 times their own weight, and the diameter of the fibers can be varied depending on the needle’s bore.
The researchers demonstrated this by accurately lifting various objects, including a cocoon, a steel bolt, a lab tube floating on water, a scalpel partially buried in sand, and a wood block – all from a distance of about 12 centimeters.
Material inspired by a superhero
“If you look at nature, you will find that spiders cannot shoot their web. They usually spin the silk out of their gland, physically contact a surface, and draw out the lines to construct their webs,” said Lo Presti.
“We are demonstrating a way to shoot a fiber from a device, then adhere to and pick up an object from a distance. Rather than presenting this work as a bio-inspired material, it’s really a superhero-inspired material.”
While natural spider silk is still markedly stronger than the human-made fibers, continual innovation promises to bridge this gap, opening up an array of possible technological applications.
“As scientists and engineers, we navigate the boundary between imagination and practice. That’s where all the magic happens,” said Professor Fiorenzo Omenetto, director of the Silklab.
“In this case, we wanted to reverse engineer our silk material to behave the way nature originally designed it, and comic book writers imagined it.”
The study is published in the journal Advanced Functional Materials.
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