Gloves that let a person crawl up flat, sheer surfaces like Spider-Man does now exist. Skeptical? Watch Elliot Hawkes, a mechanical engineer at Stanford who led the team that pioneered this breakthrough, test them out.
“To work, the surface you’re climbing needs to be relatively smooth; like glass, varnished wood, polished stone, or metal,” Hawkes says, “but you can attach and detach with very little effort, and to make [the gloves] stick all you have to do is hang your weight.”
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Over the past decade, scientists around the world have been trying to mimic the incredible stickiness of the gecko foot. But until now, engineering these materials to work at a human scale was a seemingly insurmountable challenge. It’s not that the materials weren’t sticky enough—it’s that no one was able to figure out how to delicately balance the strain of a climbing human hand across a big patch of adhesive. In a study published this week in the Journal of the Royal Society Interface, however, Hawkes and his colleagues describe how they engineered a solution.
Says Kellar Autumn, a biomechanical engineer at Lewis & Clark College who studies gecko adhesion was not involved in this project: “This is a really big deal. I’ve been dreaming about this for about 15 years, since we first discovered the mechanism that makes geckos stick to walls. And this is proof that we finally understood it well enough to make a person climb a building.”
Scaling Up
Millions of insects, and a few species of vertebrates such as geckos, have evolved to stick to vertical surfaces. Yet large animals never managed the same trick.
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There’s a reason, Hawkes says. It’s law of physics called the square cube law, which pretty much says that the bigger you get, the more volume you must have in relation to your surface area. (If you square a creature’s surface area, you must cube its volume so that its body can support its own weight.) That’s why you don’t see a 50-foot-long gecko or a Godzilla-sized lizard.
Still, there have been hints that scaling a system of gecko-like adhesion for humans is not impossible. Eric Eason, a physicist at Stanford who helped develop these new gloves, points out that geckos sticky pads are actually inefficient—only a small fraction of the pad ever touches a flat surface, and their weight is rather unevenly distributed across it.
“Perfection is not something that evolution or biological systems really care about,” Eason says.
This fact has encouraged scientists, who calculate that a slightly larger than hand-sized amount of gecko-like material should be enough to support a climbing human. You’d just need to take advantage of all the material, though, and somehow balance the strain of the hanging human in a uniform way. It’s no easy task. You’d be operating at close to the theoretical limit of the adhesives’ stickiness, and too much strain at any one point could cause the entire system to fail.
Strange Springs
To solve this problem, Hawkes and his colleagues developed a dry-adhesive called PDMS microwedges. Unlike duct tape or super glue, this reptile-inspired adhesive works via clingy hair-like nanofibers. These nanofibers flatten out when pulled downward against a surface and grip via electromagnetic attraction (called the van der Waals force) but can be pulled off easily with a perpendicular tug.
Using springs, they anchored 24 microwedge patches to a flat plate that a person could grab with their hand, the idea being that the 24 patches distribute the force of a climber. However, this is actually a well-tested recipe for failure. Normal springs won’t distribute weight as evenly as you’d need. Worse, when a single patch is pulled past its breaking point, the failure can avalanche across the entire plate.
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Here’s the key to Hawkes’ system: Instead of using ordinary springs to anchor the adhesive patches, they used springs made of a shape-memory alloy. While normal springs become tenser as you pull them like a rubber band, the scientist’s shape-memory alloy springs actually become softer and less tense, like stretching bubblegum.
Anchored by these weird springs, each of Hawkes’ microwedges distributed the weight of a clinging climber across the plate with near perfection. Hawkes could easily scale a glass wall, and the scientists have calculated that the gloves could be used by anyone up to around 200 lbs. And if one wedge ever fails, the plate simply self-corrects.
“When I first heard about this, I thought it was unbelievably clever,” Autumn says.
Skyscrapers and Space Junk
Still, there are a few limitations to this gecko tech. Hawkes says the gloves will not work in the rain, and need a relatively flat surface to function. The adhesive material tends to accumulate dirt during use, reducing their effectiveness over time. Fortunately, cleaning the microwedges is as simple as pressing them against a piece of scotch tape.
Perhaps the most exciting part of this new discovery is what’s to come next, as scientists and engineers figure out the best way to use this adhesive. The researchers’ leg-assisted scaffolding is a great start, and according to Autumn, we’ll soon see devices like gripping kneepads or gloves with a moldable shape.
Hawkes and his colleagues are already finding other interesting uses for their invention: They’re currently working with NASA’s Jet Propulsion Laboratory to find ways to attach the dry-adhesives to robots that could fling away space junk.
Source: https://t-tees.com
Category: HOW
