Imma Perfetto
Cosmos science journalist
US scientists have created their own version of Peter Parker’s iconic web fluid.
The silk fibre liquid can be shot out of device and immediately solidifies once exposed to air. It forms a string that can stick to and lift objects more than 80 times their weight.
“If you look at nature, you will find that spiders cannot shoot their web,” says Marco Lo Presti of Silklab at Tufts University in the US, first author of a paper describing the research in the journal Advanced Functional Materials.
“They usually spin the silk out of their gland, physically contact a surface, and draw out the lines to construct their webs. We are demonstrating a way to shoot a fibre 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.”
Liquid stream of silk solidifies to a fibre, adheres to and lifts glass laboratory beaker. Credit: Marco Lo Presti, Tufts University
The building blocks of the web fluid come from the cocoons of the Bombyx mori silkworm, which are boiled in a special solution to break down and extract the main component – a fibrous protein called silk fibroin.
“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,” says Lo Presti.
The acetone caused the silk fibroin to form a semi-solid hydrogel over hours. But a web-slinging vigilante like Spider-Man needs to create his webs instantly, so the researchers added another ingredient to the mix: dopamine.
As well as being an important molecule in the brain, dopamine is also used in making adhesives. It’s addition to the silk mix accelerated the solidification process to near instantaneous, by appearing to pull water away from the silk.
Liquid stream of silk solution solidifies to a fibre, adheres to and lifts several steel bolts from a petri dish filled with sand. Credit: Marco Lo Presti, Tufts University
Now, for the web-shooter component used to spin the fibres in the air, the researchers used a coaxial needle with 2 concentric holes. They shot the silk fibroin-dopamine solution through the inner hole and the acetone through the outer one.
This resulted in a thin stream of the silk solution surrounded by a layer of acetone, which triggered its solidification. The acetone then evaporated mid-air, leaving behind a fibre attached to whichever object it was initially aimed at.
The diameter of the fibres could be varied from that of a human hair to about half a millimetre, depending on the size of the needle’s bore.
The researchers enhanced the silk fibroin-dopamine solution even further with chitosan (derived from insect exoskeletons) which gave the fibres up to 200 times greater tensile strength, and a borate buffer, which increased the stickiness about 18-fold.
While far from being able to support a costumed man swinging from building to building, or stop a runaway train in its tracks, the web-shooter can pick up smaller objects – such as a cocoon, a steel bolt, a laboratory tube floating on water, a scalpel partially buried in sand, and a 5g wood block from about 12cm away.
