Geckos are evolution’s pro rock climbers. Their famously sticky feet don’t use glue or large hooks to grip almost any surface — geckos’ feet stick using the forces that bind individual molecules together, and we are getting closer to replicating it. Ask the Stanford grad students climbing a glass wall with rubber hexagons.
The gecko’s sticky secret is in the hairs on their feet. They are covered with millions of hairs known as setae, which have hundreds of even finer microscopic “split ends” that amplify the molecule-binding Van der Waals forces between the hairs and a climbing surface. Researchers have so far made sticky surfaces that work in more or less the same way using carbon nanotubes and micro-scale rubber wedges. But these, like the geckos’ implements, have only worked for small weights.
New research published today in the Journal of the Royal Society Interface has seemingly overcome this restriction, and is sending grad students up walls.
The problem with creating a synthetic gecko foot to support a human is scalability. Oddly enough, a gecko’s pads can support less and less weight as the surface area of the pad increases. For example, at the level of the microscopic hairs, a small surface area can support a tremendous amount of stress. As the surface area gets to the size of a whole foot, however, this ability to support drops off significantly. That doesn’t matter much for a tiny gecko, but if you want to support a person with gecko-like tech, scalability is the main problem.
Following the scalability relationship that the researchers found in tokay geckos, modern adhesive methods would need climbing pads at least 10 times the size of a human hand to support a 70 kg person. That would look ridiculous.
To get around this problem, the Stanford University researchers lead by engineer Mark Cutkosky created a surface that mimicked what geckos were using while being more efficient when scaled up. Using microwedges made of a polymer material called PDMS, the team constructed hand-sized hexagonal pads that consisted of 24 individual tiles each. These tiles were arranged and connected using springs and artificial tendons that distributed the load evenly across each tile.
The design of this plate allowed the researchers to do the obligatory “Can it climb up a wall?” test, which also was a success. Unlike the data the team collected on gecko feet, their “degressive load-sharing” design stayed just as sticky across a wide range of different loads, could remain sticky after continuous use, and was easily detached from the wall by simply changing the direction of force —just like geckos do it.
Stanford’s sticky Gecko-Man pads probably won’t be for turning Toby McGuire’s into wall-crawlers however. According to Technology Review, Mark Cutkosky hopes “to use the adhesives in manufacturing equipment, making grippers for manipulating huge solar panels, displays, and other objects without the need for suction power or chemical glues.” NASA reportedly is interested in the grip-tech too, but for their robots.
Robots that can climb any surfaces, even in zero-g. Hmmm….
IMAGES: by Matt Reinbold;