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article imageNew Adhesive Material Developed by Revealing Nature's Secrets

By Bob Ewing     Jul 18, 2007 in Science
A team of scientists with support from the National Institute of Dental and Craniofacial Research (NIDCR) have developed a new adhesive thanks to the gecko and the mussel. The adhesive can handle both wet and dry conditions.
What do you get when you take the dry adhesive properties of the gecko lizard and supplement that with the underwater adhesive properties of a mussel? A new adhesive that may one day be used to making more durable and longer-lasting bandages, patches, and surgical materials.
A team of scientists, who received support from the National Institute of Dental and Craniofacial Research (NIDCR), which is part of the National Institutes of Health, were able to merge two of Nature’s most elegant strategies for wet and dry adhesion to achieve this result.
The project’s results were published last week in the journal Nature. The new material is being called geckel nanoadhesive, and this new material proved in initial testing to be adherent under both dry and wet conditions. Tests also demonstrated that the new adhesive performed better under both extremes that the previous gecko-based synthetic adhesives.
“Our work represents a proof of principle that it can be done. 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.”
Phillip Messersmith, D. D.S., Ph.D., a scientist at Northwestern University in Evanston, Ill. and the senior author on the paper.
According to Messersmith he was inspired to pursue this line of research approximately two years ago when he noticed an article about the adhesive force of a single hair from the foot of gecko.
Geckos are well-known for their ability to climb walls and other steep and dry surfaces. They do so as the result of a natural adaptation of the hairs that cover the soles of their feet.
Each gecko hair is about one-tenth the thickness of a human hair and will split multiple times at the ends. Each split end contains cup-like structures that are called spatulae and this increases the hair’s surface area. The gecko makes multiple contacts with any surface that it touches. There are approximately a half million hairs on each foot, and it is estimated that a gecko has a billion spatulae to use for climbing walls.
According to Messersmith, the article that he was reading stated that gecko adhesion doesn’t work well in water. This gave Messersmith, who studies the underwater adhesion of mussels, an idea.
The idea was to coat each synthetic gecko-inspired polymer, known as a pillar, with a man-made adhesive protein inspired by the mussel. This had not been tried and according to Messersmith, if it worked, a new and potentially superior direction in designing temporary adhesive materials might develop.
As it turns out, Messersmith’s idea paid off and his team designed a small nanopolymer array that that mimicked the natural spatial patterns of the hair on the foot of a gecko. The team then coated their creation with a thin layer of a synthetic compound.
The compound that they used mimics the reversible bonding action of a mussel adhesive protein. The team had been studying this compound for the past several years.
The initial experiments were led by graduate student Haeshin Lee and the team 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. In addition, the dry adhesive force of the pillars also improved when coated with the compound.
“That actually wasn’t so surprising to us. The mussel-inspired adhesive is extremely versatile in that it can bond reversibly to inorganic surfaces under wet and dry conditions.” ” Lee, the lead author on the study.
According to Lee, the next research hurdle was to determine whether or not their hybrid geckel nanoadhesive would continue to stick to surfaces after multiple contacts. In the past this has been a major challenge for other gecko-based adhesives. These adhesives stick well at first but then lose their ability to adhere after a few cycles of contact with a tipless cantilever.
Lee developed a camera, in order to visualize the work, which involved using the cantilever and repeatedly touching it down. The result of this work was that the geckel hybrid maintained 85 percent of its adherence under wet conditions after 1,100 contacts with the tip, while under dry conditions, the level of adherence was 98 percent.
“This isn’t quite a home run, but it’s somewhere in between a double and a triple,”
According to Messersmith, the results are extremely promising; however, there still remain practical problems that need to be addressed. One problem is critical ,how to find a way to reduce the fabrication costs so that geckel will be commercially viable. commercially viable.
The ability of geckel to adhere underwater is a value added feature that may help it reach the marketplace.
According to Messersmith, the production of geckel may result in the development of patches, one day, that can be applied on the inside of the cheek to cover damaged tissue.
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