In the field of bionics, the gecko is regarded as a true master of adhesion. This reptile can attach itself to almost any surface and walk around on the ceiling upside down – it can even “stick” to polished glass without difficulty.

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Did You Know…

…that Gecko Feet Stick Better than Any Glue?

In the field of bionics, the gecko is regarded as a true master of adhesion. This reptile can attach itself to almost any surface and walk around on the ceiling upside down – it can even “stick” to polished glass without difficulty. The gecko owes this ability to the millions of fine hairs on its feet, all of which are forked like tree branches. The tip of each hair splits into a thousand even finer adhesive hairs just 100 micrometers long that, at a width of six micrometers, have a diameter one tenth of that of a human hair. These are tipped with even finer filaments a mere 200 nanometers in diameter.

Visualizing these fine hairs through a microscope presents quite a challenge – since the hairs do not conduct any electrical current at all, it is all but impossible to view them through an electron microscope. In order to find out why they stick so well, researchers at Lewis & Clark College in Portland, Oregon, collected specimens of feet from geckos and spiders with similarly remarkable properties and examined them using a Carl Zeiss helium-ion microscope that scans its subject with a helium-ion beam. This process generates images at a resolution and contrast that have set new standards for microscopy.

The secret of gecko feet lies in what are known as “van der Waals forces.” These occur between atoms or molecules whose electrical charge is asymmetrically divided – the negative charge dominates at one end of the molecule, the positive at the other. These occur between atoms or molecules whose electrical charge is asymmetrically divided – the negative charge dominates at one end of the molecule, the positive at the other. Researchers found that the force of the whole toe as well as the individual microscopic hairs was practically identical on water-repellent and water-absorbent surfaces. Therefore, the gecko’s secret is primarily based on the minute structure of the tiny adhesive hairs on the soles of its feet. In addition, the fineness and density of the structures increase proportionately to the weight of the animal’s body, meaning that it can still stick to the ceiling even when it is fully grown.

16 November 2011

 

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