Spiders’ silk is one of the most amazing materials we know of; five times stronger than steel and pound for pound even stronger than Kevlar. Last week, a post-doc scholar from Stanford used a new technique to examine silk fibre and discovered some surprising new properties of this incredible biomaterial.
Normally only parts of the fibre can be studied, but Kristie Koski used a century-old-technique to examine the elastic nature of the entire spider’s web. This previously-overlooked technique is called Brillouin spectroscopy and involves shining laser light onto the silks, producing sound waves. This reflects some light back to the spectrometer. Koski describes it as “a bit like plucking the string of a violin, only we never have to physically touch the string to play it.” Since this is non-destructive, it can be used to find subtle variations in tension across specific parts of the fibre.
This shed light on some previously unknown properties of spiders’ silk. Firstly, the stiffness of the web varies between different fibres and areas instead of being uniform, which could help protect the web from damage. Another property of spiders’ silk is supercontraction. This occurs in high humidity (when it rains, or simply in morning dew) when the silk absorbs water causing some fibres to shrink, in some cases to half their size. This seems inconvenient, and there are several hypotheses as to why this would occur. One of them is that supercontraction tightens the web when wet, so it does not sag from the weight of the water droplets. This couldn’t previously be tested because there was no way to examine whole webs. But with this ‘new’ technique Koski showed that the silk does stiffen with increased humidity, supporting this tightening hypothesis. This could also aid the spiders when spinning the web because by adjusting the water content they could adjust the properties of the silk.
Koski hopes that learning more about spiders’ silk could help us engineer materials with similar properties to create new strong materials that mimic, and perhaps even improve on, nature.
Kristie J. Koski,Paul Akhenblit, Keri McKiernan & Jeffery L. Yarger (2013), Non-invasive determination of the complete elastic moduli of spider silks, Nature Materials
