Spider-Man probably inspired more than a few comics fans to imagine walking on walls. Well, take note, superhero wannabes. Cornell University researchers say they've come up with a palm-size liquid-adhesion device that could enable just that sort of arachno-riffic move.
Similar research into adhesion technology has taken its cue from the gravity-defying gecko, but the Cornell team looked elsewhere--to a beetle native to Florida that can stick to a leaf's surface, through wet adhesion, with a force 100 times its own weight.
Observing the beetle's bonding method, which involves applying surface tension across many micron-size droplets, Cornell researchers Paul Steen and Michael Vogel posited that a similar principle could be applied to create load-bearing Post-it-like notes and shoes or gloves for people seeking Spidey-like traction.
The scientists detail their findings in this week's Proceedings of the National Academy of Sciences. Their research was funded by the Defense Advanced Research Projects Agency and the National Science Foundation.
To get a sense of how the device works, think of the way two wet glass slides stick together. Steen and Vogel's silicon wafer device works in much the same way (watch a video demonstration of it here). A flat metal plate with micron-size holes sits atop a plate holding a liquid reservoir. In between is another porous layer. An everyday 9-volt battery pumps tiny droplets of water through to the top layer and the surface tension of the exposed drops makes the device grip another surface.
But what happens when you want to come down from your wall perch?
The leaf beetle, in addition to its amazing strength, can switch off its bonding contact points, and the "Switchable Electronically Controlled Capillary Adhesion Device" out of Cornell can be turned on and off as well. To do that, the electric field is reversed, and the water gets pulled back through the tiny holes, breaking the micro-bonds that the droplets create between the device and the other surface.
"In our everyday experience, these forces are relatively weak," said Steen, a professor of chemical and biomolecular engineering. "But if you make a lot of them and can control them, like the beetle does, you can get strong adhesion forces."
The scientists created one prototype with about 1,000 300-micron-size holes that can hold about 30 grams--the weight of more than 70 paper clips. They found, however, that as they downsized the holes and put more of them onto the device, it could support additional weight. A one-square-inch contraption with millions of holes sized at 1 micron each, for example, could hold more than 15 pounds--clearly far from enough to sustain a human climber, but a big wall shimmy in the right direction.