Geckos have an uncanny ability to crawl cling to just about any surface. They can even hang upside down from polished glass with no great effort.
The secret to this ability lies in the structure of millions of microscopic hairs that line the skin of a gecko's footpads, called setae. A secret that scientists have unlocked and are now well on the way to being able to duplicate.
These tiny setae are covered with equally tiny mushroom-shaped caps to maximize the surface area each hair comes in contact with. These hairs take advantage of electrostatic Van Der Waals forces, which are responsible for a great deal of intermolecular attraction. Articles with more detailed explanations of Van Der Waals forces can be found below under the "Further Information" section.
Though the forces exerted by the individual hairs are tiny, spread out over the millions of setae they add up to a substantial adhesive power. If a typical 2.5 oz gecko has every single setae in its toes in contact with a surface, it could support nearly 300 lbs of weight. A square meter of the same material could hold up a typical family car.
After the mystery of the gecko’s stickiness was unraveled in 2000, numerous attempts were made to replicate it in the laboratory. These early efforts concentrated mostly on using artificial polymer-based setae, and only replicated about a third of the gecko’s adhesive force. More recent efforts in 2008 by a US team led by Zhong Lin Wang of Georgia Institute of Technology have met with much more success using carbon nanotube setae with spiraling ends. This new carbon nanotube adhesive is able even able to do the gecko one better, doubling its effective sticking power.
The setae stick tight when force is applied laterally to them. In other words, if you press the synthetic gecko material against a surface and push in any direction parallel or at an agle to the surface—up, down, sideways—it will stick fast. Hence, anything placed on a wall would stick, because gravity will exert this force in a desired direction.
However, If pulled away directly perpendicular to the surface, the individual setae pop away one by one, and the material can be pulled off fairly easily. This is very similar to what the gecko itself does, and is one of the properties that allow it to scurry about despite having super-sticky feet.
Another advantage of the gecko’s biology is that though the setae as a group sticks to large surfaces very well, they exerts much less force on smaller particles, and dirt and other contaminants will fall away from the hairs after a few steps, the vertical motions shaking them loose. Synthetic gecko skin can also use the same techniques to be self-cleaning, with just a few vertical taps on a surface to clean them of any major contaminants. Carbon nanotube setae are also naturally hydrophobic and would shed any water-based material, and most kinds of dirt along with it.
Because of this, tape and adhesives based on gecko skin can be used over and over again repeatedly. Also, one could run a finger over the surface of gecko tape without getting stuck; only when pressure is applied will its adhesive properties take hold.
However, synthetic gecko skin has only limited success on wet surfaces, and its adhesive effectiveness is greatly diminished. Gecko tape already applied to a dry surface would be able to be immersed in water with little effect, but forming any new bonds underwater would be only a fraction as strong of what it would be capable of otherwise. Real life geckos are also unable to stick to teflon, so we can assume synthetic gecko skin would have the same limitation with similar materials.
The earlier polymer versions of synthetic gecko skin has already been put to use in products such as gecko glue and geckel tape (which combine synthetic gecko skin with an adhesive based on sea mussel proteins, so that it works equally well on both dry and wet materials.) The much stronger and more resilient carbon nanotube version is in development, but so far would be too expensive for commercial production; a single post-it-note sized piece of carbon nanotube gecko tape would cost roughly $1000. However, as techniques for synthesizing carbon nanotubes become more widespread and more efficient, the cost may come down drastically.
Some near future applications for synthetic gecko skin materials include:
-- Reusable, waterproof bandages
-- Stronger bandages and sutures
-- Multiple-use, super-strong tape
-- Quick armor patches on fighting vehicles (carbon nanotube version)
-- Emergency patches for spacesuits and spaceships (carbon nanotube version)
-- Adhesive astronaut boots (to replace the need for magnetic boots)
-- No-slip interlocking mechanical joints
-- High-grip vehicle tires
-- No-slip work boots and shoes
-- No-slip climbing gear, gloves, and boots
Also called climber bots, stickybots, or geckobots. These are basically small robots equipped with one or more climbing surfaces coated with synthetic gecko skin, allowing them to adhere to just about any surface.
For now, these are envisioned to be small maintenance drones designed to skim over the surface of aircraft and spacecraft to check for faults and defects. In the future, as robotic technology progresses, they may be used to perform actual maintenance themselves, either independently or at the direction of a human operator.
This could also lead to true go-everywhere bots that could traverse any terrain or obstacle, even vertical walls. Such automatons could prove very useful for exploration, rescue operations, espionage, and combat.
When one describes the capabilities of synthetic gecko skin to someone, one fictional character always seems to come foremost to mind: Spider-man. Is it possible, using this technology, to allow someone to climb up vertical surfaces like the Marvel Comics super-hero?
In a word, yes. Perhaps not quite with as much speed, precision, or style, but it can be done.
Some have suggested producing gloves and boots coated with synthetic gecko skin to be able to perform this feat, but it may actually be better to build them into a full-body suit or harness in order to better redistribute the weight and to avoid slippage (the outside of the gloves are super-adhesive, but the insides aren’t.) It might also prove prudent to have auxiliary contact points at the knees, elbows or even along the shins and forearms, to ensure a comprehensive grip. The gecko skin material may be super strong, but the material its gripping might not be well anchored and the weight of the climber may make it give way. Hence, having multiple potential contact points would prove beneficial.
Any user of such a climbing harness would have to be trained in its use beforehand. Climbing would require a good deal of skilled coordination, as a user would need to make sure he or she is ‘planted’ on the surface securely before detaching a limb and moving it forward. It would probably also be a somewhat slow process for safety’s sake. Unlike Spider-man, a climber doesn’t have inhumanly-fast reaction speed nor miraculous webbing he can shoot at a nearby building should he miscoordinate his climb and find himself falling.
However, combined with other climbing equipment and a decent amount of skill and experience, such harnesses can make climbing a much more potentially safe experience. The only downside is that a gecko skin climbing harness would likely be quite expensive.
Van Der Waals Force:
Gecko Skin Materials