Frankly, this is not the easiest subject I had to talk about.. 'cause I have a real phobia of these small animals. But since I've been wondering many times why they can stick to a wide variety of surfaces without falling down, I thought it would be interesting to share with you what I've discovered. Here we go!
First, what is a gecko (for those who don't know)?
Geckos are reptiles, and more precisely squamates. They are part of the group of animals known as "lizards" in common language. As a family of reptiles, they are very adaptable, and we find these animals in many countries, such as those of equatorial, tropical and temperate zones, as well as in deserts, bush, rainforests, mountainous areas.
Geckos, like all reptiles, are poikilothermic, meaning that their body temperature varies according to the external conditions. That's why depending on their species, they will adopt a behavior aiming at maintaining their temperature in an adequate range, by exposing themselves to the sun or, on the contrary, by protecting themselves from it.(Wikipedia).
How geckos defy gravity?
Geckos have fascinated people for thousands of years. In ancient Greece, the philosopher Aristotle wondered how the reptiles could walk upside down. But at that time, no one had an appropriate answer for him. Even when scientists got into the act in the last 150 years, they still had trouble cracking the gecko’s secret. Step by step, however, they narrowed down the possibilities. They finally discovered that this ability was because of their toes. So let's first get familiar with it :
The b picture (meso-structure) shows geckos toes lamellar structure.
These lamellar structures are divided as we can see in the pictures below, c (micro-structure) and e (nano-structure). The toes (fractals) of the gecko are covered with setules or setae (hair-like) which branch out into spatulae. The size of the setae and spatulae are tiny. A setula is 110 micrometers long and 4.2 micrometers wide. Each setula contains several hundred to thousands of spatulae measuring 200 nanometers long and wide. The surface of a gecko's leg is about 220 mm2. There are 14,400 setulae per mm2, which makes about 6.5 million setulae for the whole gecko. This particular anatomy allows a gecko of 50 grams to be able to support 20 N (over 2 kg) that is to say over 40 times its weight! As a comparison, it is as if someone weighing 60 kg (132 pounds) could support a mass of 2.4 tons.Scientists have discovered that the angle of gecko toe hairs also contributes to this stickiness, making it possible for them to stick and unstuck their feet and sprint 20 body lengths per second.
Geckos' inspired technologies :
It is thus by being inspired by the model of the gecko that, in 2007, Nicola Pugno, an Italian scientist at the polytechnic institute of Turin, emitted for the first time the idea of developing a completely adhesive combination. But, to realize this project, the scientists also had to count with the so-called Van Der Waals forces which are weak interactions, or bonds, that are created between molecules under the effect of their own electric fields because under the gecko's legs, the billions of hairs are attracted to each other and thus create an adhesive force. Instead of the capillary system of the lizard, Nicola Pugnoa used a carbon nanotube. But there was the problem of dirt because the dust can weaken the intensity of the Van Der Waals forces and thus the whole adhesive system. In addition, there was the problem of muscular fatigue, because even when suspended from a ceiling, the muscles continue to work.
Since then, several innovations have seen the light of day, such as Geckskin™ which is composed of stiff fabrics—such as carbon fiber or Kevlar—with soft elastomers, such as polyurethane or polydimethylsiloxane (PDMS). The key innovation of Geckskin™ was the integration of a soft elastomer (the pad) with a stiff fabric (the skin), allowing the pad to drape over a surface to maximize contact. Further, as in natural gecko feet, the skin is woven into a synthetic tendon, yielding a design that plays a key role in maintaining stiffness and rotational freedom. The last result is an adhesive device that is powerful, easily removed, and leaves no residue.
In the field of adhesive nanotechnology, man-made materials have been designed to imitate the gecko's super adhesive ability. But artificial versions are not strong as geckos toes quite yet, but they're good enough to allow a full-grown man to 25 feet up a glass wall.
Sources:
Geckos are not only fascinating but also they can also be important allies, as they actively contribute to the control of many other health pests such as cockroaches, flies, moths, mosquitoes! I hope you found this interesting and have learned something new. Meanwhile, take care and may God bless you. See you next week!
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