Reversible Adhesive That Mimics Snail Secretion

Super-strong, reversible adhesive that works like snail secretion Anyone who has tried to use a single adhesive tape more than once knows that its stickiness won't be nearly as effective the second time. Drawing inspiration from nature, researchers have made progress toward creating a durable yet recyclable adhesive that could be used for resealable envelopes or gravity-defying boots. In a new study published in the Proceedings of the National Academy of Sciences, Penn Engineers present a strong, reversible adhesive that uses the same adhesion mechanisms as snails. The work was directed by Shu Yang, a professor in the Department of Materials Science and Engineering and the Department of Chemistry and Biomolecular Engineering, working with Hyesung Cho, a postdoctoral researcher in Yang's laboratory who is now at the Korea Institute of Science and Technology, as well as Penn Engineering graduate students Gaoxiang Wu and Jason Christopher Jolly. Laboratory member Yuchong Gao also contributed to the research. Snails secrete mucus to form an epiphragm; a slimy layer of moisture that the snail uses to protect itself from drying out and that allows the creature to be temporarily cemented in place. Yang and his team discovered that polyhydroxyethyl methacrylate (PHEMA), a polymer they work with in the laboratory, has unusual adhesive properties similar to a snail's epiphragm: PHEMA is rubber-like when wet and hard when dry. When moistened, PHEMA conforms to small grooves on a surface, allowing the material to stick to that surface. But what matters is what happens when PHEMA dries: It becomes as hard as a plastic bottle cap, but uniquely, it does not shrink. Instead, the material hardens in the cavities, firmly anchoring itself to the surface. "When it's conformable and solid, it's like super glue—you can't pull it apart. But magically, you can rewet it and it comes off effortlessly," says Yang.