Have you ever wondered why a spider's web does not droop in the wind or fling back like a trampoline? According to a new study by an international group of scientists, the answer to this lies in the physics of a 'hybrid' material produced by spiders.
Pulling on a sticky strand in the orb web of a garden spider and allowing it to snap back reveals that the strand never droops but always remains rigid – even when stretched to multiple times its actual length. This happens because any wobbly thread is instantly wound within the small droplets of wet glue that surround and cover the main gossamer fibers of the capture spiral of the web. Researchers from the University of Oxford, UK and the Université Pierre et Marie Curie, Paris, France have illustrated this occurrence in the PNAS journal.
The team studied the particulars of this 'liquid wire' method in spiders' webs and used it to form compound fibers in the laboratory which, similar to the spider's capture silk, compress like liquids and spread like solids. These unique insights may result in innovative bio-inspired technology.
The thousands of tiny droplets of glue that cover the capture spiral of the spider's orb web do much more than make the silk sticky and catch the fly. Surprisingly, each drop packs enough punch in its watery skins to reel in loose bits of thread. And this winching behavior is used to excellent effect to keep the threads tight at all times, as we can all observe and test in the webs in our gardens.
Professor Fritz Vollrath, Department of Zoology, Oxford University
The unique properties witnessed and investigated by the researchers depend on a slight balance between droplet surface tension and fiber elasticity. Essentially, the group were also able to reconstruct this method in the lab, using droplets of oil on a plastic filament. Additionally, this synthetic system acted similar to the spider’s natural winch silk, with reels of filament winding and unwinding within the oil droplets as the strand stretched and contracted.
Spider silk has been known to be an extraordinary material for around 40 years, but it continues to amaze us. While the web is simply a high-tech trap from the spider's point of view, its properties have a huge amount to offer the worlds of materials, engineering and medicine. Our bio-inspired hybrid threads could be manufactured from virtually any components. These new insights could lead to a wide range of applications, such as microfabrication of complex structures, reversible micro-motors, or self-tensioned stretchable systems.
Dr Hervé Elettro, Doctoral Researcher at the Institute Jean Le Rond D'Alembert, Université Pierre et Marie Curie