Gecko + mussels = biomimetic underwater adhesive

Gecko + mussels = biomimetic underwater adhesive

Gecko + mussels = biomimetic underwater adhesive
mongabay.com
July 19, 2007

Scientists have developed a new adhesive material based on the properties of mussels and gecko lizard. The researchers say the biomimetic design could produce more durable and longer-lasting bandages, patches, and surgical materials.

Writing in the current issue of Nature, a team of researchers describe the hybrid material, which they call a geckel nanoadhesive, as the first case where “two polar opposite adhesion strategies in nature have been merged into a man-made reversible adhesive.”

“Our work represents a proof of principle that it can be done,” said Dr. Phillip Messersmith, a scientist at Northwestern University and the senior author on the paper. “A great deal of research still must be done to refine the fabrication process and greatly reduce its cost. There’s no reason to believe that these improvements can’t be achieved, but it’s going to take time.”

A news release from NIH/National Institute of Dental and Craniofacial Research describes Messersmith’s inspiration for the adhesive.

Dr. Messersmith said the inspiration for the geckel nanoadhesive came about two years ago when he noticed an article about the adhesive force of a single hair from the foot of gecko. As lizard fans have long marveled, geckos climb walls and other dry, steep surfaces not by producing a glue-like substance but through a natural adaptation of the hairs that cover the soles of their feet.

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Roughly one-tenth the thickness of a human hair, each gecko hair splits multiple times at the end. These split ends contain cup-like structures called spatulae that vastly increase the hair’s surface area. Whereas a human hair touches a surface just once, the gecko makes multiple contacts with the suction-like spatulae. With roughly a half million hairs on each foot, scientists estimate a gecko has a billion spatulae at work as it scampers up a wall.

Messersmith knew that researchers have attempted for several years to produce synthetic adhesives based on the adherence strategy of the gecko. What caught his eye in this article is gecko adhesion doesn’t work well in water. Messersmith, who studies the underwater adhesion of mussels, had an idea. What if each synthetic gecko-inspired polymer, called a pillar, was coated with a man-made adhesive protein inspired by the mussel” As Messersmith mused, nobody had ever tried it and, if successful, this hybrid approach might spawn a new and potentially superior direction in designing temporary adhesive materials

As reported in Nature, Messersmith’s idea turned out to be correct. He and his colleagues designed a small nanopolymer array that mimicked the natural spatial patterns of the hair on the foot of a gecko. They then coated their creation with a thin layer of a synthetic compound. This unusual compound mimics the reversible bonding action of a mussel adhesive protein that Messersmith’s group has studied for the past several years.

In their initial experiments, which were led by graduate student Haeshin Lee, they found that the wet adhesive force of each pillar increased nearly 15 times when coated with the mussel mimetic and applied to titanium oxide, gold, and other surfaces. The dry adhesive force of the pillars also improved when coated with the compound.

While the results are promising, Messersmith said commercialization is still several years away.

“Any time that you fabricate an array of nano pillars of this type over large areas, you must have a very effective way of doing it without losing the efficacy of the approach,” said Messersmith. “We’ll also need to reduce the fabrication costs to make geckel commercially viable.”

Nevertheless, Messersmith envisions bandages that can be applied inside one’s cheek will someday be developed.