New synthetic spider silk almost like the real thing

A new way of making artificial spider silk can produce a kilometre of thread from 10 rice grains’ weight protein – and it’s almost as strong as the natural fibre.

Researchers from China, Spain, Sweden and the UK drew inspiration from spider anatomy to build a spinning device which makes synthetic silk cheaper and easier than harvesting the real stuff. The work, unveiled in Nature Chemical Biology, might ramp up production of large quantities of silk for manufacturing.

Spider silk is made of protein molecules called spidroins. These molecules start in the silk glands, where they’re kept in highly concentrated solution.

When it’s time to spin a web, this concentrated solution is squeezed through a narrow duct. Along the duct, the environment becomes more acidic, with the pH gradually lowered from 7.6 to around 5.7, and pressure increases.

This acidity and pressure force the spidroins to link together in what’s known as a “lock-and-trigger mechanism” and form long silk fibres which are stronger than steel on a per weight basis.

Strength plus low density means spider silk could be used in settings such as aviation or protective gear.

But making it on a commercial scale has proved tricky. While synthesising spidroin molecules is easy enough – bacteria and yeast, for instance, can be genetically programmed to produce it – spinning the thread is easier said than done.

So Marlene Andersson from the Swedish University of Agricultural Sciences, Qiupin Jia from Donghua University in China and colleagues built their own duct from a glass capillary tube. The tube’s tip – only 10 to 30 microns wide – was dipped in an acidic solution.

They enlisted Escherichia coli bacteria to produce spidroins. A litre of bacterial culture yielded around 125 milligrams of pure spidroin protein.

As the spidroins were pumped through the capillary tube, the combination of pressure and acidity forced the proteins to link into fibres, which were wound onto a spool.

They managed to wind around a kilometre of silk from a litre of bacterial culture. And when they tested the fibre, it was more elastic and stronger than any other artificial spider silk they knew of – albeit less well than real silk.

The technique is not only cheap and simple, the researchers write, but the spidroin solution could easily be stored at 4 °C for weeks and at −20 °C for months without losing its ability to form fibres.

It could also be improved by, “the introduction of gradual changes of pH and ion composition” rather than the abrupt change produced by dipping the tube tip in acidic solution.