Gecko are well-known for their incredible ability to climb vertical walls, cross ceilings and hang on the underside of tree branches. Their feet have been well-studied in the past, and have led to some interesting bio-mimicry technology, such as ways to seal wounds and sticky hand-held paddles to help soldiers scale walls. Yet ongoing research is showing just how complex the geckos’ adhesion system really is. 

Geckos stick to surfaces because their toes are covered in millions of microscopic hairs called setae. Each seta splits off into hundreds of even smaller bristles called spatulae. These spatulae get so close to the contours of the wall or tree that they tap into a special kind of electromagnetic force called van der Waals force. Van der Waals forces involve the creation of a physical bond between the electrons from the gecko hair molecules and the electrons from the wall molecules. As the electrons interact with each other they create an electromagnetic attraction.

Scientists have discovered how the balance of forces acting on the gecko, and the angle of its toe hairs, contribute to the creation of its successful stickiness. The setae on the gecko’s feet don’t stand up straight at a 90-degree angle, but instead branch off at oblique angles. Researchers have developed a mathematical model that shows that as the hairs bend at angles closer to horizontal, the surface area that the geckos stick to increases, and the geckos can support more weight. This system makes it possible for geckos to stick and unstick their feet so rapidly that they can race across surfaces at 20 body lengths per second. If, however, the surface is covered in too much moisture, the sticking powers are reduced. 

They have also discovered that setae are ultraflexible. When a gecko changes direction quickly or leaps to another surface, the setae and spatulae have to absorb huge amounts of energy and redirect it. The flexibility and stretchiness of the setae make this possible.