A Stanford mechanical engineer is working on an adhesive based on a gecko's sticky foot which would allow people to climb smooth, vertical surfaces.
Mark Cutkosky has already developed a lizard-sized robot, the Stickybot, and says it can climb surfaces such as wood paneling, painted metal and glass. He's working on scaling it up to produce a product called Z-Man which would allow humans to climb in the same way.
"Unless you use suction cups, which are kind of slow and inefficient, the other solution out there is to use dry adhesion, which is the technique the gecko uses," he says.
The material is strong and reusable, and leaves behind no residue or damage.
The toe of a gecko's foot contains hundreds of flap-like ridges. On each ridge are millions of hairs, ten times thinner than a human's, which fray at the ends into smaller strands called spatulae. The spatulae are so tiny - a few hundred nanometers across- that they interact with the molecules of the climbing surface.
As a result, a gecko can hang and support its whole weight on one toe by placing it on the glass and then pulling it back. It only sticks when you pull in one direction.
"It's very different from Scotch tape or duct tape, where, if you press it on, you then have to peel it off," says Cutkosky. "You can lightly brush a directional adhesive against the surface and then pull in a certain direction, and it sticks itself. But if you pull in a different direction, it comes right off without any effort."
Using a one-way adhesive is important for climbing because it requires little effort to attach and detach a robot's foot.
"Other adhesives are sort of like walking around with chewing gum on your feet: You have to press it into the surface and then you have to work to pull it off. But with directional adhesion, it's almost like you can sort of hook and unhook yourself from the surface," Cutkosky said.
To mimic this, Cutkosky and his team came up with a rubber-like material with tiny polymer hairs made from a micro-scale mold.
The adhesive has 'hairs' about 20 micrometers wide. As the robot moves up the wall, it peels and sticks its feet to the surface with ease, says Cutosky.
He's now working on a version that turns in the middle of a climb, which means rotating the foot."The new Stickybot that we're working on right now has rotating ankles, which is also what geckos have," he said.
"Next time you see a gecko upside down or walking down a wall head first, look carefully at the back feet, they'll be turned around backward. They have to be; otherwise they'll fall."
There's a video of the Stickybot in action, here.