This shows a silkworm 'pulling' silk from its body. Photo: University of Sheffield.
This shows a silkworm 'pulling' silk from its body. Photo: University of Sheffield.

New insights into how animals spin silk could lead to new, greener ways of producing synthetic fibers, according to academics at the University of Sheffield in the UK.

In a paper in Nature Communications, researchers from the University of Sheffield's Department of Material Science and Engineering report that animals spin silk by pulling rather than pushing it out of their bodies. They suggest that if this process can be copied in an industrial setting, it could improve how synthetic materials are processed and offer more environmentally-friendly alternatives.

Conventional synthetic textiles are made by extrusion, which involves pushing a liquid feedstock through a dye and then exposing it to harsh chemicals and large changes in temperature to induce solidification. However, silk can solidify into a fiber at room temperature, leaving behind just water – therefore causing less environmental damage.

"Silk is one of the most promising green biomaterials, and could be the perfect replacement for nylon and polyester based clothing," said lead author Jamie Sparkes, a PhD student in the University of Sheffield's Natural Materials Group. "Traditional production process for silk is both arduous and time-consuming, but if we can bypass that by mimicking nature in an industrial setting, we could improve not only silk, but also how we process our synthetic materials."

The researchers examined how animals, including silkworms and spiders, push materials like silk out of their bodies.

"While it is easy to assume that silk is propelled out of the body like we see in comic books, we wanted to put that to the test," said Chris Holland, head of the Natural Materials Group. "By combining computer models with experimental data and practical measurements, we determined the forces needed to squeeze unspun silk down the animals' silk gland and spin a fiber."

"We found that to spin silk by extrusion (pushing), means a silkworm would have to squeeze itself hard enough to generate more pressure than a firing diesel engine," said Sparkes. "This isn't possible as the animal's body would be unable to contain that pressure. It seems that you can't squeeze silk like a tube of toothpaste."

However, by measuring the forces required to pull silk from the animal's body, the researchers found that it was well within the capability of the silkworm to pull a fiber, a process they refer to as pultrusion. This involved adapting a rheometer, a machine normally used to measure the viscosity of liquids, into a highly sensitive spinning wheel, capable of measuring the forces needed to spin.

"If I gave you a piece of chewing gum and asked you to make me a fiber, you wouldn't push it through your teeth as it's too stiff. You'd grab one end and pull it out – and that's what the silkworm and spider do," explained Holland.

This story is adapted from material from the University of Sheffield, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.