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July 30, 2007
New “Glue” Marries Sticky Properties of Geckos and Mussels
Inspired by two creatures that have real sticking power, researchers have created a new type of adhesive that holds tight both in and out of water and can be repeatedly removed and re-attached, almost like a sticky note. With further improvements, the adhesive may one day lead to more durable and longer-lasting bandages, drug-delivery patches and surgical materials.
The scientists named their new adhesive "geckel," because it combines the mechanical stickiness of a gecko lizard's foot with the chemical stickiness that lets a mussel hold fast to underwater surfaces. According to Dr. Phillip Messersmith and his colleagues at Northwestern University, it's the first time that 2 completely different 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," he says. Their research is supported in part by NIH's National Institute of Dental and Craniofacial Research (NIDCR).
Geckos have a remarkable ability to climb walls and other steep surfaces and even scurry upside down, but not because of sticky secretions. Rather, the strong but temporary adhesion of their feet arises from densely packed fine hairs covering their foot pads. Each hair splits multiple times at the tip, resulting in a greater number of contact points, which strengthen the adhesion force. Several research teams have tried to create adhesives based on gecko-like strategies. To date, however, these substances all lose their ability to re-adhere after a few cycles of contact, and none work well when wet.
As reported in the July 19, 2007, issue of Nature, Messersmith and his colleagues used nanotechnology to create swatches of microscopic polymer pillars that mimicked the multiple contact points of the gecko's foot hairs. Each pillar was just 400 nanometers in diameter — about twice the width of the gecko hair's split ends. The scientists coated some of the nanopillar arrays with a very thin layer of synthetic polymer that imitated the underwater adhesive properties of mussel "glue" proteins.
The researchers found that, in a wet environment, the adhesive force of the gecko-like pillar array was 15-fold higher with the mussel-like polymer coating than without it. The dry adhesive force also improved when the pillars were coated with the polymer. In addition, the polymer-coated arrays maintained their adhesive performance for more than 1,000 contact cycles in both dry and wet environments.
Although the versatility of this new hybrid adhesive holds promise for many medical applications, Messersmith says his group must tackle several practical problems. "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," he says.