Researchers from the University of California, Berkely and Nanjin University of Aeronautics and Astronautics studied gecko feet for inspiration for wall-climbing robots. They conducted experiments to study gecko feet and develop climbing robots that can adjust quickly to accommodate the shifting weight and slippery surfaces.

The spotted belly of a Tokay gecko used by UC Berkeley biologists to understand how the animal's five sticky toes help it climb on many types of surface. Source: Yi Song

The team observed geckos running horizontally along walls to learn how they use their toes to climb on a variety of surfaces. Gecko toes can stick to smooth surfaces because of intermolecular forces. They can uncurl and peel their toes in milliseconds. Gecko toes have up to 15,000 hairs per foot. Each hair has split ends for close surface contact. The toes only stick in one direction. They grab when pulled in one direction and release when pulled in the opposite direction.

During the experiments, the team ran geckos sideways along a vertical wall and made high-speed recordings to watch toe orientation. The sideways movement allowed the team to distinguish the downward gravity from forward running forces and test the idea of toe compensation. They also used a frustrated total internal reflection technique to measure the area of contact of each toe. This technique made the toes light up when they touched a surface.

Researchers found that geckos can run sideways just as fast as they could climb upwards. The toes easily and quickly realign to gravity in a given situation. The toes on the front and hind top feet shifted upwards during sideways wall climbing and running, acting like the front toes of front feet during normal climbing.

To test how gecko toes change for different surfaces, the team added slippery patches and strips of irregular surfaces to the wall and ran the geckos again. Geckos overcame these hazards thanks to their multiple small toes. Redundancy allowed the toes in contact with the surface to reorient and distribute the load. The toe softness allowed them to conform to rough surfaces. The toes allow agile locomotion by distributing control across all surfaces. The distributed control of a biological adhesion could be used effectively in robotics. Gecko feet are inspiring new ideas for robot feet, novel grippers and unique manipulators.

A paper on this research was published in the Proceedings of the Royal Society B.