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Sci-Tech

Bone yarn brings new meaning to 'knitted skullcap'

Researchers at ETH Zurich have developed a way to spin good quality yarn from slaughterhouse waste.

Mittens knitted from gelatine yarn. Philipp Stössel/ETH Zürich

There are a number of materials from which to spin yarn. Animal fibres, such as wool or silk; plant fibres such as cotton and bamboo; and synthetic fibres such as rayon and polyester. Now, researches have shown it can be spun from slaughterhouse waste, such as bone.

More specifically, it can be made from gelatine, a product derived from the collagen in skin, connective tissue, bones and cartilage left over once an animal has been slaughtered for its meat.

The yarn, developed by 28-year-old Ph.D. student Philipp Stössel, of professor Wendelin Stark's Functional Materials Laboratory at ETH Zurich, has qualities similar to merino wool, and could, the laboratory hopes, provide a natural, environmentally friendly alternative to synthetic fibres.

A paper on the three-year project has been published in the journal Biomacromolecules.

Stössel got the idea for the yarn when he noticed that adding organic solvent isopropyl to a solution of heated liquid gelatine caused the protein to separate and fall to the bottom in a mass. Removing this with a pipette, Stössel was able to press the material into an elastic thread.

To spin the gelatine into yarn, the protein is fed through an array of parallel syringe nozzles to produce fine filaments with a diameter of just 25 micrometers, half the thickness of a human hair. These are guided over Teflon-coated rollers, which are kept damp with ethanol to prevent the filaments from sticking together and to accelerate the hardening process.

Cross section of the gelatine fibres showing porosity. Philipp Stössel/ETH Zürich

This process produces 200 metres of filaments per minute. These are then twisted together to form yarn using a spindle, much like wool or cotton fibres are twisted together, to form a strong thread. Stössel twisted 1,000 individual filaments into his yarn.

While Stössel's fibre has been successfully used to knit a mitten for demonstration purposes, there is still some work to be done before the yarn is viable. Gelatine dissolves and expands in water, which makes it fabulous for cooking purposes, but this makes it not so great for clothing.

So that any garments knitted from gelatine yarn don't dissolve in the rain, Stössel has been working on water resistance by treating it with chemicals. First, he used an epoxy to better bond the gelatine fibres together, then formaldehyde for hardening and finally, lanolin, a natural wool grease, to make the fibres more supple.

The next step in the research is to find ways to improve the water resistance of the yarn. Although it is comparable to sheep's wool in other ways, such as its porosity, which makes it an excellent insulator, the gelatine yarn cannot yet match the water resistance of sheep's wool.

It does, Stössel said, have quite a pleasing appearance, however. The gelatine fibres are smooth, unlike wool, which is covered in tiny scales. This gives the yarn an "attractive luster," he said.