With adhesives, it’s hard to have it all. They’re usually either strong or reversible. And getting both reversible and strong adhesion can be even more difficult if the target surface is rough or uneven. A team led by Shu Yang of the University of Pennsylvania and Anand Jagota of Lehigh University has cracked the problem, developing an adhesive that can conform to irregular surfaces while being both strong and reversible.
The researchers were inspired by the mucus structure that snails use to hang on to rough surfaces such as rocks or trees, called the epiphragm. The new material is made of a poly(2-hydroxyethyl methacrylate) hydrogel cross-linked with ethylene glycol dimethacrylate. In its soft, hydrated state, the material conforms to target surfaces. As the hydrogel dries, it locks onto the surface with an adhesive strength of as much as 892 newtons per square centimeter, which is strong enough to be considered a superglue. When rehydrated, the adhesive releases and returns to its original shape. The researchers used the snail-inspired adhesive to move delicate objects such as butterfly-wing scales. Yang says the group is now working on adhesives that don’t require water to release. “With the understanding of the mechanism of adhesion and reversibility, our next step is to find a new material that can be activated by heat, light, or electrical field,” she says. (Proc. Natl. Acad. Sci. U.S.A. 2019, DOI: 10.1073/pnas.1818534116).