Everybody knows that geckos can climb straight up vertical surfaces, hanging upside down with ease. This ability is possible thanks to an intermolecular phenomenon experienced by the geckos’ toes, a force known as van der Waals’ force. It was unknown however, exactly how geckos can adhere so strongly to a surface, yet dash away in an instant. Researchers have used mathematical modelling to understand this apparent paradox, publishing their findings in the Journal of Applied Physics.
A study published over a decade ago provided evidence that geckos utilise molecular forces to ‘stick’ to walls. Instead of being smooth or scaled, the bottoms of geckos’ toes are heavily bristled. This fuzzy surface is composed of an ocean of hair-like projections known as ‘setae’, a Latin word meaning ‘bristles’. Though these setae are small (microscopic in fact), they split into yet finer structures called ‘spatulae’, derived from the Latin word for ‘broadswords’.
These toe-tipping spatulae are flexible and dynamic structures which are extremely small. They are so small, that as the gecko walks on a wall, the spatulae integrate with the physical structure of the surface. Since the spatulae and wall are in such close proximity, the molecules composing both structures begin to interact. Positive and negative charges within the spatulae and wall form electromagnetic bonds, thus providing the gecko with ‘dry adhesion’. Utilising these intermolecular van der Waals’ forces, a gecko can even suspend its entire body weight on just a single toe attached to a surface – pretty, pretty convenient.
The mystery explained by the current study however, was how the geckos disable these bonds in order to rapidly run across the surface. The answer came in the form of mathematical modelling, which revealed the secrets of the setae. The setae (which bear the spatulae), grow out from the toe pads and connect with the wall or surface on a slant, as opposed to parallel or right-angled contact. And since the setae are so flexible, as the gecko applies weight to its toes, this weight further presses the setae onto the surface and maximises their sticky contact points. The oblique angle of the setae/wall contact points also makes it easier for the setae to quickly detach. When a gecko runs (sometimes at 1 m/second) and lifts its toes from the wall, pressure is redistributed, pulling the setae from the wall at an oblique angle, somewhat like removing a Band-Aid.
Apart from being extremely cool and interesting, this research helps to further refine human biomimetic technology by incorporating the fine-scale properties of setae and spatulae into future designs.
Originally published on Thinkinc.org.au
Original article from: http://livescience.com/47307-how-geckos-stick-and-unstick-feet.html
Research paper from:http://scitation.aip.org/content/aip/journal/jap/116/7/10.1063/1.4892628