Anyone who’s tried to use a single piece of adhesive tape more than once knows that its stickiness won’t work as effectively the second time. Thanks to inspiration from nature, researchers have made progress toward creating a durable yet reversible adhesive, one that could create resealable envelopes or gravity-defying boots. In a new study published in the Proceedings of the National Academy of Sciences, Penn Engineers demonstrate a strong, reversible adhesive that uses the same mechanisms of adhesion as snails.
Shu Yang, a professor in the Department of Materials Science and Engineering and in the Department of Chemical and Biomolecular Engineering, led the study along with Hyesung Cho, a postdoctoral researcher in Yang’s lab who is now at the Korea Institute of Science and Technology, and Penn Engineering graduate students Gaoxiang Wu and Jason Christopher Jolly. Lab member Yuchong Gao participated in the research as well.
Snails secrete mucus to form an epiphragm, a slimy layer of moisture that the snail uses to protect from dryness, which allows the creature to cement itself in place temporarily. Yang and her team discovered that a polymer they were working with in the lab, polyhydroxyethylmethacrylate (PHEMA), also had unusual adhesive properties akin to that of the snail’s epiphragm: PHEMA was rubbery when wet but rigid when dry.
When wet, PHEMA conforms to the small grooves on a surface, which allows the material to stick to a surface. But what matters is what happens when PHEMA dries: It becomes as rigid as a plastic bottle cap, but, uniquely, doesn’t shrink. Instead, the material hardens into the cavities, fastening itself securely to the surface. “When it’s conformal and rigid, it’s like super glue. You can’t pull it off. But, magically, you can rewet it, and it slips off effortlessly,” says Yang.
Read more at the Penn Engineering blog.