The legendary ability of geckos to cling to walls and ceilings may rely on electrical forces, according to researchers who dragged geckos across several surfaces.
Until now, geckos were thought to be able to stick to surfaces using van der Waals forces. These result from the temporary movement of charged particles within a molecule, which creates a polarised, magnet-like state. As a result, attractions can form between molecules in the animals’ feet and the surfaces they cling to.
Alexander Penlidis at the University of Waterloo in Ontario, Canada, and his colleagues wondered if electrical forces, which result from the movement of electrons from one surface to another, might play a role, in the same way that a balloon rubbed on clothing sticks to a wall. To find out, the team measured the electric charge on geckos’ feet as they gently dragged them across Teflon or a silicone rubber called PDMS.
Penlidis’s team discovered that as soon as a gecko’s toe pad touched a surface, the pad became positively charged while the surface became negatively charged, creating an electrostatic attraction.
When the team compared the strength of the electrostatic force with the strength of the adhesion between the gecko’s foot and the surface, it found that the forces were of a similar strength. This suggests that the electrostatic force is the dominant attractive force responsible for a gecko’s sticky feet, says Penlidis.
“This is an important discovery, and suggests electrostatic forces could contribute to adhesion in geckos on some surfaces such as Teflon,” says Kellar Autumn of Lewis & Clark College in Portland, Oregon. But Autumn argues that the other previously established forces still play the dominant roles, especially when geckos climb surfaces that are submerged in water, where electrostatic charges cannot develop.
Journal reference: Journal of the Royal Society Interface, DOI: 10.1098/rsif.2014.0371