2009 Volume 3
Silks make not only interesting natural materials but also, in the context of their use by the animals that produce them, fascinating natural composites. Importantly, the material properties of a silk depend not only on the chemistry and subsequent folding pattern of the silk protein themselves but also on the hierarchical structure of the poly-protein ﬁbre. Both, in turn, depend to a large extend on the conditions under which a ﬁbre has been spun and thus depend on the animal’s spinning behaviour. Not surprisingly, this gives the animal a high degree of ﬂexibility in which to use its materials. And, if the materials (and typically silks are multi-faceted) are integrated into structures, then those too can have a range of ultimate properties, depending on the animal’s building behaviour. As both materials and structures have evolved over hundreds of millions of years, much can be gleaned and learned concerning highly adapted and often optimized structure-property-function relationships on the material level as well as on the composite level.
Individual silk ﬁbres can range in diameter from 20 to 7000 nm depending on species, animal size, silk type and spinning conditions. The hierarchical structure of a silk ﬁbre can range from very simple to complex i.e. a singular ﬁlament consisting of its molecular chains folded into regions with differing degrees of order to, respectively, bundles of ﬁlaments aggregated and layered into ﬁbre-ropes and covered with coatings of specialist compounds .
Presented here are two very different silk ﬁbre and composite types: the many silks and light-weight webs of spiders and the singular silk and solid cocoon of lepidopteran “silkworm” larvae.
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