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A reversible glue that mimics the underestimated properties of dried snail mucus has been found to be strong enough to support the weight of an average man.
Scientists who tested the slime-inspired product found that two post-stamp-sized sticky squares were enough to support a weight of 87 kg (192 lb) in the form of a volunteer student engineer .
The unusual substance overcomes a problem that researchers in the field have been struggling with for decades, that glues can be weak and reversible, or strong and irreversible, but never, it seems, strong and reversible.
Scientists from the University of Pennsylvania pondered the problem when they realized that molluscs might have the solution. "Snails are the perfect example," said Shu Yang, professor of materials science, who led the work. "When they move, the mucus that they produce is a viscous liquid, but when it dries, they stay stuck."
Yang and his colleagues created the new glue from hydrogel, a form of polymer network containing a lot of liquid water. In the wet state, the hydrogel infiltrates and spreads into the smaller cracks and contours of a surface. But when it dries, it locks.
Experiments with the new glue showed that it was incredibly strong in the dry state, but quickly softened and relaxed gently when water was added to rehydrate the hydrogel. Laboratory tests have shown that the glue can be applied and detached from the butterfly wings without harming delicate fabrics.
Rather than a liquid squeezed into a tube, the adhesive is applied to thin, thin patterned plates featuring tiny channels to allow water to enter and exit. The glue dries naturally in the air, or more quickly when it is heated, and comes off with a well placed water jet. The use of water to peel off the adhesive means that it can only be used in dry environments, although Ms. Yang said her team was looking for similar materials that would would rather be softened with heat or electricity.
The hydrogel glue imitates something that snails use to protect themselves from dehydration in dry weather. Instead of sliding over a layer of wet mucus, mollusks create a hard, dry layer that locks onto the grooves and troughs of the surface they are on. This membrane, known as an epiphragm, seals the base of the snail and prevents it from losing too much water.
As with an epiphragm, the glue works best on rough surfaces, but Mr. Yang said that the adhesive was still effective on the glass. "The surface does not have to be very, very rough, because any type of surface has a certain roughness," she said. The details of the work are published in the Proceedings of the National Academy of Sciences.
Nurses would welcome the presence of a reversible glue. Medical journals describe many cases of people sticking their ears and sticking their eyelids after taking the adhesive for drops for the ears or eyes. In one case, a carpet upholsterer glued his hands with glue. He was only released when the doctors referred him to a cosmetic surgeon who dissolved the acetone glue.
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