A gecko's foot is nature's greatest adhesive. These tiny lizards belonging to the family Gekkonidae can stick to virtually any surface without glue, Velcro-like interlock, suction, friction, or even electrostatic attraction.
The secret lies in the gecko's feet. Microscopes have shown that one foot alone has about one million keratinous hairs, called setae (pronounced "see-tee"), which are tipped with spatula-like structures, called spatulae. These hairs get so close to the surface, that an intermolecular bond, the Van der Waals force, (which is a weak attractive force between molecules and atoms because of the positioning of the electrons within the interacting particles) which would normally be insignificant compared to other natural forces, becomes strong because of the closeness of the seta and the surface, and because there are so many places where they come in contact.
A gecko running across the ceiling will attach and detach it's feet to and from the surface about fifteen times per second. This is possible because of the "rolling," curling motion a gecko's toes will perform when it's walking, a gecko's toes will curl up to remove itself, and uncurl to attach. The uncurling motion performs the parallel pull against the surface, which strengthens the bond 600-fold, and the technique to the curling motion when the gecko lifts it's foot is at roughly a 30 degree angle, determined to be the "only" angle to easily detach a seta from the surface, so there is no difficulty in walking.Measurements have proven that each seta is about ten times more effective at adhesion than estimated the entire animal would be.
Geckos seem to only use a fraction of the hairs when walking on a vertical surface, although they have been known to be able to hang from a ceiling by only one toe. The force of a hair engaged with a surface is so strong, that a single hair could lift an ant, while the million or so hairs on a Tokay gecko's foot (an area about the size of a dime) could lift a child of about 20.5 kilograms (45 pounds).Even though the setae work extremely well adhering to a surface smooth like glass, it's possible that in the natural world, waxy coatings on leaves may hinder adhesion by resisting intermolecular interactions (Autumn, 2000). In the laboratory, a gecko may not need more than ten percent of their setae to stick to glass, they may need to use more to move around on vegetation.In conclusion, this natural adhesive is compact, dry, powerful, and even self-cleaning: Unlike any other known adhesive.
REFERENCES
AUTUMN, Keller; Chan, Wal pang; Fearing, Ronald; Full, Robert J.; Hsieh, S. Tonia; Kenny, Thomas W.; Llang, Yiching A.; Zesch, Wolfgang. "Adhesive force of a single gecko foot hair", Nature. 8 June, 2000. http://www.nature.com
SANDERS, Robert. "It's not glue, suction, or static electricity that keep geckos from falling...", University of California Berkeley Campus News. Berkeley, California. 2000.
