PALO ALTO, Calif. – It doesn’t mean experiments taking place at Stanford’s Biomimetics and Dexterous Manipulation Lab are any less science-y just because they sometimes resemble scenes from a “Spider-Man” or “Mission: Impossible” movie.
“You see those movies as a kid and think, ‘If I could do that, it would be great,’” says the lab’s Elliot Hawkes. So he did do that. And it was great.
The Stanford team has created paws that look like paddles and use the same scientific principles employed by the sticky feet of geckos to allow humans to scale glass walls. The university’s legendary mechanical engineering department has a history of creating its own legion of Silicon Valley superheroes, but it wasn’t until the work of Hawkes’ four-man team that companies like Marvel or Mattel showed much interest in the school’s awesome amygdalae – or “lizard brains.”
After pioneering work a decade ago in “sticky” robots that aped the gecko’s grip, a new generation of biomimeticists took the next step: putting a human face on lizard paws. That face belonged to Hawkes, a graduate student whose Ph.D. research culminated with him scaling a sheer glass wall like a certain cinematic web-spinner.
The Stanford students have patents pending on all this and have already begun negotiations with toy companies eager to get some cold hard cash to stick to their fingers. A Swiss entrepreneur has scheduled a meeting with the gecko gloves team in January to discuss possible rock-climbing applications.
And there is already a project in the works with NASA and the Jet Propulsion Laboratory to use a version of gecko gloves to grab space junk. “The idea is to go up very gently, touch onto a solar panel or fuel tank and reel things in,” says Mark Cutkowsky, a member of the mechanical engineering faculty who was part of the four-man team. “It turns out that gecko-inspired adhesives are one of the very few technologies that will work in space, where you’ve got a vacuum and very low temperatures.”
Despite the alluringly alliterative name, gecko “gloves” are actually paddles, with slots to hold the climber’s hands tight to the back pingpong paddle-sized devices.
Hawkes was the guinea gecko, attempting to match the super-sticky moves of nature’s most impressive climber. “One of the most important attributes of their adhesive is that it’s controllable,” Hawkes says, “like tape that you can turn on when you want it to stick, and turn off when you don’t.”
But a gecko’s body weighs only a few ounces, and Hawkes was dragging 150 pounds up the side of that building. Humans also lack the tremendous upper body strength that allows geckos to run more than a meter per second over rough and shiny surfaces alike. “People are not built like geckos, so you have to give them some tools to help them use the adhesive,” says Cutkowsky, “something like a movable ladder.”
So that’s what they did. “It turns out there’s not much load going through your hand when you’re climbing,” Hawkes says. “Most of the load is going through your foot.” That meant transferring much of the load from the paddles – with their 24 adhesive tiles – to the feet, which the team did by attaching rope and small climbing rungs to the paddles. Each tile holds about 10 pounds, and if the load isn’t spread equally among all the tiles, the person wearing the gecko gloves would go ker-splat.
“To climb with it feels fairly magical,” Hawkes says, holding up one of the paddles. “You have your entire body weight hanging from this much adhesive. Each time you put it on, you kind of expect it to fail. And then it works.”
The fiberglass tiles have an adhesive surface of 100 microns – the thickness of a human hair – that’s applied by hand. Its surface is dry and not at all tacky to touch, using a phenomenon of molecular attraction and repulsion known as “van der Waals force” to create grip. A gecko uses the same process to attach and release as it slithers over vertical surfaces, or hangs from ceilings.
“With our adhesive, the goal is to get as much intimate contact as possible over the entire area to make that van der Waals force scale up to something significant,” says Eric Eason of the Stanford research team, which had its findings published last month in the Royal Society journal Interface. Lifted straight up from the surface, the gecko tiles release instantly. But when the sheer force of gravity pulls the tiles sideways when climbing, the wedges bend over and come into contact, creating more adhesion.
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