Spider silk has been an active area for biomimetics research for several years. Spinoff companies have been launched in anticipation of commercial gains. However, despite the enthusiasm and commitment of research staff, the prizes are still elusive. Whilst the main goal is to produce fibres that are as strong and as flexible as spider silk, there are other aspects of the natural material that have attracted the interest of researchers. One of these concerns the ability of webs to be a site for dew collection.
“When Lei Jiang first observed the phenomenon, he was intrigued. “How does that happen?” he wondered. After all, he says, “if you took a human hair, water would not stick to it like that”. His initial curiosity led to an almost five-year-long study. The findings could have implications for the design of materials for water collection and for the efficiency of chemical reactions.”
Not only do webs attract dew, the droplets are able to hang stably on the silk fibres. This suggests the presence of a microstructural mechanism. All polymeric fibres have a microstructure and spider silk is no exception. SEM images reveal a series of amorphous regions (called puffs) and crystalline regions (called joints). The nanofibrils are highly hydrophilic: enhancing wettability and favourable for condensing dew. The puffs have a very open structure and are semi-transparent in images. However, when water starts to condense, the puffs shrink – first to “opaque bumps” and then to “spindle-knots”. As they shrink, tiny water droplets coalesce to form larger drops with movement from joints to spindle-knots.
“Further work revealed that movement of the droplets towards the knots is directed by two forces acting together: the force generated by a gradient of surface energy on the fibrils and the one produced by the spindle shape of the knots. “This is quite different from other reported surfaces, on which drops are driven just by individual forces,” says Jiang.”
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Is there an ID perspective on this? Wherever researchers recognise “design principles” in the natural world, the answer is, of course, ‘yes’. The presumption with ID is that design features imply functionality, whether or not we know the details. Dew gathering is a unique and remarkable feature of spider silk simply because other fibres do not display such behaviour. The authors comment:
“We observed such directional water collection behaviour only with wetted silk fibres (that is, wet-rebuilt silk) from the cribellate spider Uloborus walckenaerius; in contrast, silkworm silk and nylon fibres with a uniform structure did not exhibit the directional water collection phenomenon.”
Whether evolutionists can explain ‘how the spider came to gather dew’ is more uncertain. Even with functionality identified, perfecting this highly engineered system makes it most reasonable to infer intelligent, rather than natural, causation.
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