A non-invasive laser light-scattering technique has been used to further the understanding of spider silk — an advance that could lead to materials for bulletproof vests and artificial tendons.
The scientists at Arizona State University (ASU) used the technique to obtain a variety of elastic properties of silk from several intact spiders’ webs.
‘Spider silk has a unique combination of mechanical strength and elasticity that makes it one of the toughest materials we know,’ said Prof Jeffery Yarger of ASU’s Department of Chemistry and Biochemistry, and lead researcher of the study. ‘This work represents the most complete understanding we have of the underlying mechanical properties of spider silks.’
Spider silk is a biological polymer related to collagen but is more complex in its structure. The ASU team of chemists is studying its molecular structure in an effort to produce a range of materials.
The array of elastic and mechanical properties of spider silks in situ, obtained by the ASU team, is believed to be the first of its kind, and is claimed to ‘greatly facilitate’ future modelling efforts aimed at understanding the interplay of the mechanical properties and the molecular structure of silk used to produce spider webs.
The team published the results of its study — entitled ‘Non-invasive determination of the complete elastic moduli of spider silks’ — in Nature Materials.
‘This information should help provide a blueprint for the structural engineering of an abundant array of bio-inspired materials, such as the precise materials engineering of synthetic fibres to create stronger, stretchier and more elastic materials,’ Yarger said in a statement.
Other members of Yarger’s team, in ASU’s College of Liberal Arts and Sciences, included Kristie Koski, at the time a postdoctoral researcher and currently a postdoctoral fellow at Stanford University, and ASU undergraduate students Paul Akhenblit and Keri McKiernan.
The Brillouin light-scattering technique used a low-power laser of less than 3.5 milliwatts. Recording what happened to this laser beam as it passed through the intact spider webs enabled the researchers to spatially map the elastic stiffnesses of each web without deforming or disrupting it. This non-invasive, non-contact measurement produced findings showing variations among discrete fibres, junctions and glue spots.
Four different types of spiders’ webs were studied. They included Nephila clavipes, A. aurantia, L. Hesperus and P. viridans, the green lynx spider, the only spider included that does not build a web for catching prey but has major silk elastic properties similar to those of the other species studied.
The group also investigated one of the most studied aspects of orb-weaving dragline spider silk, namely supercontraction, a property unique to silk.
Spider silk takes up water when exposed to high humidity. Absorbed water leads to shrinkage in an unrestrained fibre of up to 50 per cent shrinkage with 100 per cent humidity in N. clavipes silk.
The results are said to be consistent with the hypothesis that supercontraction helps the spider tailor the properties of the silk during spinning. This type of behaviour, specifically adjusting mechanical properties by simply adjusting water content, is inspirational from a bio-inspired mechanical structure perspective.
‘This study is unique in that we can extract all the elastic properties of spider silk that cannot and have not been measured with conventional testing,’ said Yarger.