Gecko toe hair stickiness has been explained by scientists at Oregon State University, and this could lead to advances in adhesive technology. Essentially what was discovered was that gecko toe hairs have extensions that can turn the stickiness on and off very quickly and this is what allows geckos to run very fast up walls, on ceilings and everywhere else. A report on the study was published in the Journal of Applied Physics.
The stickiness of gecko toe hair has been studied for quite a while, but the new research has shown how the gecko toe hair works on the level of atoms. The research team, led by Alex Greaney, was able to model how van der Waals forces are at play to allow the stickiness to turn on and off very rapidly. The van der Waals force is a force of electromagnetic attraction. When the toe hairs are sticky, the electrons from the gecko toe hair molecules and electrons from the wall molecules interact and a physical bond forms. When the toe hair changes on this atomic level, the stickiness is gone.
The toes on a gecko’s feet are covered with hundreds of microscopic hairs, which are called setae. A seta is made up of smaller bristles, which are called spatula. The van der Waals force is at work in the molecules of the spatula. It is the balance of these van der Waals forces that allow the geckos to run up walls by sticking and unsticking their toes very quickly. Geckos can run at about 20 body lengths per second.
The setae sprout from the bottom of the feet of a gecko but do not stick out straight at a 90 degree angle. These setae stick out at oblique angles. The setae are also very flexible and stretchy, which allows the gecko to change angles when moving from one surface to another. The setae that cover the bottom of the gecko’s toes can create “intimate” contact with the minute variations in the surface the gecko is attaching to. Another important factor in the system is how the setae can stick or unstick without expending very much energy.
Greaney and colleagues used a mathematical model to study the toe hairs of geckos. The results from applying the mathematical model showed that geckos balance the force of gravity with their own force against a wall. This allows geckos to move their body and feet across surfaces without falling. A minimal amount of energy is used when geckos are running over a surface because the multitude of little toe hairs contact the surface and stick and unstick in a precisely integrated way.
The knowledge that has been gained about gecko toe hairs and stickiness can be applied to the development of new adhesives. There are many practical applications that could borrow the gecko mechanisms. Some have suggested that robots could apply a similar technology for moving on diverse types of surfaces. Military applications based on a gecko’s ability to run up walls and on ceilings have been suggested. Some type of paddle that has a similar adhesive quality that can be turned on and off may be developed that will allow a soldier to scramble up a wall or across a ceiling. The model for how a gecko runs along surfaces by sticking and unsticking toe hairs will certainly be considered in the development of new adhesive technology.
By Margaret Lutze