Small Gecko lizards have the amazing ability to climb and run on vertical surfaces even when they are completely smooth like glass. The adhesion ability of their foot doesn't function like glue or a sticky tape, usually our first thought when we see them running upwards a wall. If they used a glue-like physiology not only they would accumulate dirt and thus become incapacitated but they would also need a huge effort in order to unstick their foot in every step. The amazing mechanism that natural selection have provided the gecko is the subject of study in order to form similar functions artificially.---



The image above is one of the examples of artificial gecko-like adhesion materials that the robotics lab of Berkeley's electrical engineering faculty is studying. The main difference between glue type adhesion and gecko-type is that the first is comprised from a homogeneous soft material that sticks completely to the surface where the gecko's feet use relatively hard but very small and pointy appendixes in order to bond in a very precise and local manner. The adhesion is anisotropic and the bond can break effortlessly when force is applied to another direction. Another great advantage is that because of the nature of the gecko-type adhesive its structure is self-cleaning. Dirt and other small particles that can easily saturate a sticky surface has a negligible effect on it.



The images above show a gecko-type surface with a lot of dust particles (left) and the self-cleaned action of the exact same surface from use (right).

The basis of the gecko-adhesion is the small fibers and end-plates that are made mostly from beta-keratin (a hard protein similar to fingernails or hair). When applied to a surface in a specific direction, even with minimal force they form tiny local bonds that can withstand great forces. If a -small- force is applied to a unfavorable direction those bonds break with ease. The whole process by nature removes any foreign object (ex dust particles) and these properties are stable even with frequent use.



A more approachable example is the toy car in the photo above that can stand in a highly reclined glass surface because of the artificial gecko tape in its wheels.

For much more detailed and highly technical information you can visit the Gecko project website of BerkeleyRobotics lab here: Biologically Inspired Synthetic Gecko Adhesives
I highly recommend to read the FAQ first: Gecko FAQ

(in the first image, a Mediterranean house gecko I scanned myself some years ago, other images from eecs.berkeley.edu)