With a little bit of help from our slimy, shelled friends, the humble snail, scientists have developed a wickedly sticky superglue that’s strong enough to hold a human from a ceiling with just a stamp-sized patch. Best of all, just like a gecko creeping across a wall, it’s reversible and can be switched on or off as needed.
Reporting in the journal Proceedings of the National Academy of Sciences, scientists at the University of Pennsylvania set out to develop a superstrong but reversible adhesive. For inspiration, they looked no further than the natural world.
Mollusks, most notably snails and slugs, are capable of sticking to surfaces thanks to a gloopy mucus they produce. In its wet form, this allows for just the right level of stickiness while also allowing the animal to move. However, once hardened, the mollusk can attach itself to a surface for long periods of time.
While on the hunt for material like this, a member of the research team came across a hydrogel made of a polymer called polyhydroxyethylmethacrylate, known as PHEMA for short, that was rubbery when wet but rigid when dry. In this case, its reversibility is controlled by water.
Further investigations into PHEMA cemented its place as an ideal candidate. If applied to a surface in its wet state, it continues to spread into the tiny cracks and cavities, unlike other sticky materials that tend to shrink as they dry, which leaves them prone to peeling away.
"It's like those childhood toys that you throw on the wall and they stick. That's because they're very soft. Imagine a plastic sheet on a wall; it comes off easily. But squishy things will conform to the cavities," lead author Shu Yang, a professor in the Department of Materials Science and Engineering and in the Department of Chemical and Biomolecular Engineering, said in a statement.
“When materials dry, they usually shrink. If it shrinks from the surface, it no longer wants to conform to the microcavities and it'll pop out," said Yang. "Our PHEMA adhesive doesn't pop out. It stays conformal. It remembers the shape even when it's dry and rigid."
Obviously, you wouldn’t want to construct a house or a build a car with this stuff, as the rain will make short work of its stickiness. However, the researchers say an adhesive material with a water-activated reversible could have some useful applications in scientific research and medicine.
Meanwhile, scientists are also on the hunt for other adhesives that could become reversible by responding to cues, whether that be chemicals and pH or light and heat.