Friday, October 26, 2007

Glue That Sticks to Nearly Everything

For an easy-to-make adhesive inspired by mussels, possible applications abound.

By Kevin Bullis

Sticky inspiration: The chemistry of protein strands that mussels use to attach themselves to nearly any type of material (the mussel here is attached to Teflon) has helped researchers develop a new, versatile adhesive. Credit: Image courtesy of Haeshin Lee and Phillip Messersmith, Northwestern University

Multimedia •  Watch water cling to a surface coated with the new adhesive. •  See how the new adhesive creates a water-repellent material.

Flexible displays, water-purification filters, and materials that convert heat directly into electricity could be easier to make thanks to a new polymer that allows researchers to coat almost any object, even one made of Teflon, with microscopic patterns of metals and organic materials.

Researchers at Northwestern University designed the polymer to mimic a protein-based glue that mussels use to attach themselves to rocks, wood, plastic, and steel--indeed, just about any material they encounter. The researchers, led by Phillip Messersmith, a professor of biomedical engineering and materials science and engineering at Northwestern, identified an easy-to-make compound similar to active elements in this mussel glue. They found that under the right conditions, the compound forms an extremely thin polymer film on the surface of just about any material that it's applied to. This film can in turn chemically bind to a wide variety of materials that have useful functions. Many other methods for "functionalizing" materials have been developed, but according to Marcus Textor, a materials professor at the Federal Institute of Technology, in Switzerland, this one stands out because it's easy and extremely versatile. "What I find fascinating is that this is a relatively simple system," Textor says. "Often, one has to find a particular solution for a particular substrate. But this is a universal adhesive that works on many different surfaces."

The new adhesive will allow nearly any object to be easily and inexpensively coated with a veneer of metal or some other functional material, including materials that keep objects free of bacteria or encourage the growth of specific types of cells. The coatings would be thin enough that they wouldn't change the shape of the underlying object; a surgical instrument, Messersmith says, could be given an antibacterial coating without compromising its performance. One application that the Northwestern researchers have been exploring is water filters that use tiny pellets coated with the adhesive. As water runs through a cylinder full of the pellets, the adhesive pulls toxic metals out of the water by binding to them.

The researchers have also demonstrated that the adhesive can be carved into intricate patterns through conventional microlithography. If a solution containing metal salts washes over such a pattern, metal will stick only to the adhesive. This could be a way to print electronic circuits onto just about any object. Deposited on a flexible substrate, such circuits could be useful for flexible displays. The ability to create microscopic patterns of organic materials could also be useful to biologists. The Northwestern researchers have demonstrated that it's possible to create coatings that bind to a specific type of acid important for blood-vessel growth and stem-cell differentiation. The ability to deposit precise patterns of this and other organic materials could make it easier to build microfluidic devices that help explain biological mechanisms.