Engineers at Penn have shown how a superstrong reversible adhesive that works like a snail’s slime.
While strong adhesion exists, it is usually irreversible. University of Pennsylvania describes this effect using the example of pressing a picture-hanging adhesive strip against the wall and realising that it is slightly off centre.
Natural examples of strong adhesion
In the natural world, a snail’s epiphragm (the slimy layer of moisture that can harden to protect the snail’s body from dryness), means that it can stick itself in place for a long period of time.
Shu Yang, professor in the Department of Materials Science and Engineering and in the Department of Chemical and Biomolecular Engineering, added: “Geckos can put one hand down and then release it, so the gecko’s adhesion is reversible, but it’s very low adhesion. A gecko is 50 grams, and a human is at least 50 kilograms. If you want to hold a human on a wall, it’s not possible using the same adhesive. You could use a vacuum, but you have to carry a cumbersome vacuum pump. We’ve been working on this for a long time, and so have other people. And no one could have a better solution to achieve superglue-like adhesion but also be reversible.”
The reversible adhesive
In the new study, Penn engineers have been able to demonstrate the use of the same mechanism used by snails to create a strong, reversible adhesive.
Gaoxiang Wu was working on another project that involved a hydrogel made of a polymer called polyhydroxyethylmethacrylate (PHEMA) and noticed that it had unusual adhesive properties.
Yang commented: “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.”