Snapshot Issue 47 September 2008
Nothing seems more fragile than the silk thread woven by a spider. It quivers in the slightest of morning breezes and breaks with the smallest of pressures. Yet a cable of dragline silk – the thread spiders use to make the scaffolding of their webs and that from which they hang – as thick as a garden hose could support a fully-loaded Airbus without giving way! Such a material must conceal extraordinary properties.
Spidroin is the structural protein of dragline silk which is both a strong and extensible fibre. In other words: it is tough. Dragline silk is not only capable of stretching almost half its length but it can also absorb a hundred times as much energy as steel without breaking! It is indeed one of the toughest materials known to date.
Made up of different regions or modules, spidroin consists of crystalline beta sheets and amorphous regions. The crystals impart robustness to the proteins while the amorphous regions bestow extensibility. Different spider silks have different concentrations of crystals and thus different mechanical properties. And if spiders can weave threads with such extraordinary properties, can humans too?
Much research has been carried out on dragline silk with an aim to synthesize robust biomaterials. The idea is to have a deep understanding of each module in order to produce a custom-made silk fibre. Such fibres could be used to make artificial tendons or to tether satellites in space for instance. This said spiders have been spinning silk for as much as 380 million years…
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