What does it take for spider man to have the ability to climb buildings and scale glass walls like spider man? It may seemed highly impossible for normal human beings like us to achieve such superpowers, but the world’s supreme climber, the gecko is able to attach and detach its adhesive toes in milliseconds while running around on ceilings and walls.
So how does the gecko do it? The science of its adhesive toes is actually very interesting. The gecko’s toes or feet are covered with millions of microscopic hairs called setae which works like pressure sensitive adhesives. Each setae, about one-tenth the size of a human hair further branched out to hundreds of tiny split ends of the nanoscale called spatula. These hair are formed from hydrophobic sulfur-rich protein, known as keratin. The large number of these tiny structures reduces the distance and increases the surface of contact between the toes of the gecko with molecules of surfaces the glass wall or ceiling. A type of intermolecular forces known as van der waals forces allowed the toes to stick onto the wall surface strongly.
What are Van der waals forces?
In Chemistry, Van der waals forces represent relatively weak interactions between molecules as compared to strong interactions such as ionic or covalent bonds. They differ in that they are caused by temporary dipoles on molecules which arises due to the building up of electrons on end of a molecule forming a negative pole, this will repel the electrons in other nearby molecules, making them slightly positive on one end. The negative pole of one molecule will form an electrostatic attraction with the positive pole of another molecule. This attractions is temporary because the electrons are always moving and hence such forces of attractions are weak. The strength of van der waals forces increased with surface area and number of electrons, and decreases with distance.
So molecules like Iodine with a large number of electrons at an appreciable distance from the nucleus will give rise to significant attractions to hold the molecules together, making it difficult to separate these molecules at room temperature and hence Iodine is a solid.
Keller Autumn, a biologist, has been conducting studies to obtain evidence about the mechanism on how the gecko manoeuvre itself on walls without falling off.
In June 2007, he found that when properly oriented, preloaded, and dragged, a single seta in a gecko’s toe can generate 200 μN in shear and 40 μN in adhesion, more than 3000 times greater than the force required to hold the animal’s body weight. All 6.5 million setae on the toes of one gecko attached simultaneously could lift 133 kg(Autumn, 2007). With such a strong force generated by the setae, it is amazing that the gecko is able to curl and peel its toes off with ease as it moved up walls and across ceilings.
So is it possible for spider man to exist? Recent research studies that in climbing animals like the geckos, the percentage of body surface covered by adhesive footpads’ increases with body size. For humans to be able to climb like the gecko, we need to cover at least 40 per cent of our total body surface with sticky footpads. In 2014, an engineering student from Stanford managed to develop a synthetic adhesion system which improve upon the uneven load distribution on the gecko’s toes. The result is area of adhesive no larger than that of a human hand which allowed a human to climb a vertical glass wall.
(Hawkes, Eason, Christensen, & Cutkosky, 2015)
Autumn, K. (2007). G ecko Adhesion :, 32(June), 473–478.
Hawkes, E. W., Eason, E. V, Christensen, D. L., & Cutkosky, M. R. (2015). Human climbing withefficiently scaled gecko-inspired dry adhesives. Journal of the Royal Society, Interface / the Royal Society, 12(102), 20140675. http://doi.org/10.1098/rsif.2014.0675