Hold on tight!

Dock Beetle forces
The diagram of the forces shown here above also brings a solution to another problem: It is clear that the liquid is not found everywhere on the pad but mainly in a small wedge, while part of the contact is practically dry. Up to the present, scientists could not reconcile the fact that there was a liquid meniscus and that friction forces could be observed. The model designed by the researchers from Liege shows that these two types of forces actually co-exist. The formula developed by the insect is optimal since the capillary forces and the liquid enable it to adapt much better to the unevenness of surfaces than if there were only solid to solid friction forces.  “The gecko also uses fibrillar structures in the form of hairs”, explains Tristan Gilet. “But there is a fundamental difference hidden obscured by the sensationalism of the research done on it: the structures of the gecko are arranged in hierarchical form, the smallest ones are as small as a nanometre. The nanohairs of the gecko indeed need to be small enough to come into very close contact with even the slightest bump on the surface. The fact that there is no liquid to “fill in the gaps” has forced the gecko to develop extremely fine surfaces. The insect, on the other hand, has a much more promising strategy from the engineer's point of view because manufacturing hierarchical structures such as those of the gecko is complicated and they are fragile”.


This is the whole point of the research in addition to gaining an understanding of the phenomenon: being able to design a mechanism which can adhere strongly as well as detach rapidly (the insect takes dozens of steps per second and can support up to ten times its own weight!). The goal would be to use such a robotic tool in the field of micromanipulation. Currently the smallest manufactured electronic components are about 200-400 microns in size, not due to a fabrication limitation, but because smaller objects would be impossible to handle. On the other hand insects daily attach and detach structures that are only 5 microns wide (their hairs). What enables them to do so is amongst other? the presence of liquid and precise leg movements that the researchers would like to reproduce with a bio-inspired tool. 

This will be the focus of future research in the Liege and Brussels laboratories. A joined project supported by the FNRS aims to study how the liquid is secreted and channelled towards the hairs and how this is optimized by the animal. Indeed, as the insect loses liquid at each step it has to renew it . This represents a lot of energy so it must be used frugally. The researchers therefore suspect that the dock beetle has developed movements aimed at energy saving and moves in such a way that it loses? a minimal amount of liquid!

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