Nanogirl Michelle Dickinson: A coat of many strong and super-stretchy cobwebs

Female spiders tailor their silks depending on whether they are used for hunting, hanging from or cocooning eggs. Photo / Mike Scott

A coat made of cobwebs might not sound like the next fashion statement but spider silk holds a genetic secret that could be a key solution to plastics in the clothing industry.

Producing up to seven different types of silk, female spiders can tailor their silks depending on whether they are used for hunting, hanging from or cocooning eggs. By varying the composition of the proteins within the silk, spiders produce a material that is incredibly strong and also super stretchy.

This flexibility combined with strength makes spider silk one of the toughest materials in the world and one envied by materials scientists keen to reproduce the natural wonder-material.

In addition to their mechanical properties, some spiders can also change the visual properties of their silks. By producing transparent silk that reflects UV, poorly spiders can make it difficult for insects to see so they are more likely to fly into their web. Other spiders are all about the bling and infuse their silks with carotenoids making them glisten like gold.

Although spiders don't seem to suffer from the cold, if they did their silk could help them out as woven spider silk has heat-trapping, down-like properties. This makes spider silk an interesting natural material that could be used for winter and outdoor clothing, which are often made from petroleum-based plastic fabrics like polypropylene and polyester.

Spider silk could be used for winter and outdoor clothing, which are often made from plastic fabrics like polypropylene and polyester. Photo / 123rf

Decades of dissecting the bodies of spiders to analyse their hundreds of silk glands and carefully using fine-tipped tweezers to slowly coerce the silk from the spiders' bodies have helped scientists to understand how spiders make so many kinds of silk and how their composition contributes to their different properties.

Making silk seems to be easy for a spider, however, replicating this process through man-made means has been challenging scientists for years.

While spider silk seems like a magical material, trying to coerce a spider to produce only a certain type of silk and then physically extracting it for spider silk farming is almost impossible. Even if you could "milk" a spider of its silk, spiders tend to be cannibals and wouldn't tolerate the close proximity needed in a spider-silk farm.

To try and solve this problem, scientists have combined genetic analysis with synthetic biology and transferred the genes responsible for producing silk in the spider to microbes that can do the hard work without the cannibalism.

The genetically modified microbes are fed on sugar, which can come from many different cost-effective sources including agricultural waste products. The microbes then convert the sugar into a light and fluffy protein mix, which is the base for the synthetic spider silk. Although the technique works with several different microbes, researchers have found that the genetically modified form of the fungus Trichoderma reesei has the added advantage of pushing out the spider-silk residue once it's ready. The excreted protein blob is then drawn through a long, narrow tube under a high voltage where it can be purified and spun into a delicate, lightweight thread, which can be woven into a fabric.

This novel spider-silk growing method has now been used by a Japanese biotech venture and a sports clothing company to produce a coat made from sustainable and biodegradable spider-microbe material. While the silk-making process is still in its infancy and can only make a few milligrams of the material at a time, work is being done to help increase the yields for scale-up so that mass-produced outerwear clothing can be made. Who knows, if the scale-up goes well you might be wearing a spider-sourced coat next winter.