Nanotechnology Mimics Nature's Adhesive

A Glue Which Uses the Gecko's Remarkable Feet as its Inspiration

Oct 9, 2008

Scientists in recent weeks have begun to pave the way toward using nanotechnology for very practical purpose: Keeping things from falling off walls.

For decades, the remarkable ability of the Gecko lizard to climb effortlessly across any vertical surface (or even upside-down), no matter how smooth (or rough), has both baffled and intrigued scientists. If only humans could harness such adhesive powers, could there finally be an alternative to duct tape and superglue?

Believe it or not, scientists have finally achieved success in this area after several failed attempts.

By microscopically analyzing the feet of geckos, scientists have come to understand that this lizard's remarkable abilities comes from an unlikely source - tiny (microscopically tiny, in fact) elastic hairs (from 3 to 130 nanometers in length) which split at the ends into even tinier "hooks." Because these hairs are so small, they behave in a manner not dissimilar to Velcro, but on a microscopic level, which allows them to stick to even the smoothest, slickest of surfaces.

It is as a result of these hairs that geckos have the remarkable ability to hang upside from the adhesion of just a single one of their toes!

Recent advances in nanotechnology (the manipulation of microscopic entities and the creation of structures and materials using nano particles) have allowed a new possibility in this regard. In particular, the answer which has been found by scientists lies in a particular type of nanosctructure called a "carbon nanotube."

The name of this structure is really rather self-explanatory - a carbon nanotube is merely a tube made up of carbon atoms. Carbon has proven itself to be perhaps the most resilient and simple atom to use in nanotechnology because its electron structure is uniquely designed to allow ready and strong bonding with other carbon atoms, which can be used to create large, complex, and useful carbons structures... like tubes.

These nanotubes have now been manipulated in such a way that they essentially mimic the peculiar features of gecko feet, extending microscopically from a surface and then curving into a microscopic "hook."

Using these carbon tubes - which by themselves are considerably stronger than the hairs on gecko feet - scientists have created a dry adhesive (that is, a non-chemical adhesive, like Velcro) which is actually superior to the foot of the gecko, while retaining the features which make it unique: high shear adhesion and low normal adhesion.

There is an important difference between these two types of adhesion when discussing sticky stuff. One of the qualities which clearly makes gecko feet unique is that while they are clearly very sticky and work incredibly well at keeping the creature stuck to any surface, they also somehow allow the animal to lift their feet back off the wall and walk along easily.

One can imagine that a lizard foot without this quality would be rather useless. Geckos would simply get stuck to the walls forever, unable to move.

The key here is the difference between shear adhesion and normal adhesion. Once again, velcro is a great example of this. When a velcro strap adheres to itself, it provides very strong adhesion indeed, especially when pulled against itself in a way which demonstrates its "shear" strength, but when it is pulled in the right way, such as when pulling apart the velcro on shoes, it actually comes apart rather easily. This is the same sort of phenomenon which is exemplified in gecko feet and, consequently, in the human-created nano adhesive.

The nanotube adhesive created by scientists has proven to maintain incredibly high strength under shear conditions (such as when hanging objects from a wall), but is also very easily removed on such diverse surfaces as PTFE (teflon), rough sandpaper, and glass. It is this fact which makes this product remarkable, and which provides obvious potential for future uses in residential, commercial and industrial uses.

Who knows? Within the next few years carbon nano-tube driven adhesives may become the wave of the future. Look out duct tape!

The copyright of the article Nanotechnology Mimics Nature's Adhesive in Physics is owned by Isaac M. McPhee. Permission to republish Nanotechnology Mimics Nature's Adhesive in print or online must be granted by the author in writing.