Researchers led by Stanford engineer Elliot Hawkes have created a pair of gecko-inspired gloves that enable users up to 200 pounds to scale smooth, vertical panes of glass. As one biomechanical engineer put it: "This is a really big deal."
Top image via Elliot Hawkes
The secret to Hawkes' team's gloves is their efficiency. It turns out that the sticky foot-pads a gecko uses to climb, while perfectly adequate for the gecko, aren't nearly as effective as they could be. Because geckos are, well, gecko-sized, they can get away with using only a fraction of their pads' effective area. A human-sized gecko would not only need to use more of its pads, it would also need to distribute its weight more strategically. What Hawkes and his team demonstrate in this week's issue of the Journal of the Royal Society Interface is that gecko-like pads can be scaled up to human-size proportions – and work! – provided the human uses as much of the pad's surface as he can, and balances his weight just so:
"This is a really big deal," said Keller Autumn – a biomechanical engineer at Lewis & Clark College who studies gecko adhesion, but was not involved in Hawkes' project – told Popular Mechanics' William Herkewitz, who describes the breakthrough in detail:
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.
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.
"I've been dreaming about this for about 15 years, since we first discovered the mechanism that makes geckos stick to walls," said Autumn, "and this is proof that we finally understood it well enough to make a person climb a building."