Molecular Velcro Is Sticky When Wet

Aquatic creatures such as mussels are experts at sticking to wet surfaces, providing inspiration for researchers to design glues based on the animals’ secretions. But these synthetic adhesives typically require curing agents and are then irreversibly sticky. To overcome these limitations, a research group at Pohang University of Science & Technology, in South Korea, has created a new adhesive that works under water. It has molecular hooks and loops akin to the fabric structures that hold together Velcro (Angew. Chem. Int. Ed., DOI: 10.1002/anie.201209382). The team coated one silicon surface with aminomethylferrocene and another surface with cucurbit[7]uril, a large doughnut-shaped molecule. The aminomethylferrocenes (the hooks) fit snugly into the hydrophobic cavities of the cucurbit[7]urils (the loops). The sticky system is strong enough to support a 2-kg weight, even under water. The added bonus, the team says, is that the adhesive can be chemically switched off: When immersed in a solution of sodium hypochlorite, which oxidizes aminomethylferrocene, the silicon surfaces come apart with only the pull of a 0.5-kg weight. The researchers have filed a patent for their molecular Velcro, says team leader Kimoon Kim. They will work next on attaching the hook and loop compounds to polymer surfaces.