Archive for November, 2014

Artificial Gecko Feet Has Arrived

November 21st, 2014 No comments

Scientists discovered a number of years ago that the modest gecko makes use of a fascinating trick of physics to remain stuck to surfaces. A gecko’s foot is covered in ridges that exploit van der Waals forces to adhere to anything that’s sufficiently smooth. Now researchers at Stanford working with the US Defense Advanced Research Projects Agency (DARPA) have created a functional human-scale version of the gecko’s foot. Just strap these pads to your hands, and get climbing… slowly.


Physicists have known about the van der Waals force for decades, but its effects are rarely seen beyond the microscopic scale. The van der Waals force is simply an attractive force between two molecules that is not due to covalent or ionic bonding (i.e. molecule forming). It has to do with the way electrons are shared within molecules. As these negative particles shift around in the cloud surrounding a positively charged nucleus, they can occasionally cluster on one side, which gives the molecule a temporary charge differential or “dipole.” Other molecules have a permanent dipole, but the effect is the same–there’s a weak attraction between them.

The hand-sized pads designed by Stanford and DARPA are operating entirely on van der Waals force, just like a gecko There are 24 small panels on each pad the size of a postage stamp, which are arranged in slanted rows. None of the panels would feel particularly sticky if you were to touch them, but pressing the pad to a glass surface and pulling down makes it instantly stick. The large surface area of the pads ensures that it remains in place until the user lifts it. Unlike past attempts, researchers believe this design can be used for long periods of time, not just for short demos.

On a microscopic level, this silicone material works much like a real gecko’s feet. A gecko has ridges called setae on its feet, each of which is covered in microscopic hair-like projections called spatulae. This gives the gecko’s foot a much larger effective surface area than you’d think just looking at it. The artificial material developed by researchers is similar, made from a type of silicon material called polydimethylsiloxane. Each of the 24 pads is covered with microscopic slanted wedges that increase effective surface area. Arranging the gripping surface into separate pads helps the device cling to irregularities in the surface, but it still requires a mostly smooth surface to work.


Even before developing this material, researchers knew sticky gloves wouldn’t be good enough. One problem with the “Spider-Man” model of climbing walls is that most people have considerably more strength in their legs than their arms. That makes the climbing gloves insufficient to scale walls no matter how well they stick. To get around this, the researchers have attached a series of cables to each hand pad that transfers the load to the feet. There’s a rigid platform for each foot to rest on, so the climber can shift their weight back and forth, re-positioning one pad at a time then stepping up onto the now higher platform.

You can see this method at work in the video above, and it isn’t much more strenuous than climbing a ladder. However, it’s pretty slow–the video is sped up by 2 times. The team hopes future designs will make the gecko climbing system easier and faster. There’s also still work to do optimizing the micro-wedge material for less smooth surfaces and finding a way to keep it clean. This is still a big achievement as the first technology that can support a human climber using van der Waals forces.

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