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October 20th, 2007 at 9:19 am

Super Sticky Coating has ‘Mussel’

Mussels have a remarkable strategy for staying put in surf zones, despite the crashing waves: they secrete a fluid that can bond to virtually any surface.


Powerful Sticker
Haeshin Lee |

Now scientists have developed a coating that mimics the tenacious adhesion of a mussel. The coating could improve biosensors, medical devices, marine and medical anti-fouling coatings, purify water contaminated with heavy metals, and advance manufacturing methods for flexible displays.

"We demonstrated something like twenty-five different materials that this would work on," said Phillip Messersmith, professor of biomedical engineering at Northwestern University in Evanston, Ill.

He and his team report their findings in today’s issue of Science.

The coating is made from dopamine, a molecule more commonly known for it neurotransmitting abilities. Although it does not exist in mussels, dopamine contains two key chemical groups that are present in the crustacean’s holdfast — the part that helps it cling to surfaces. By capitalizing on these chemical properties, Messersmith and his team were able to mimic the mussel’s steadfast stickiness.

Creating the coating involves a relatively simple procedure free of the expensive, chemically sophisticated techniques often necessary to produce other coatings. The scientists dissolve the dopamine in water and then adjust the pH level to match a marine environment. When they do that, a chemical reaction occurs that produces a polymer in the solution.

Now any object can be dipped into and coated with the polymer, or conversely the solution can be sprayed or painted onto any surface. And like the mussel secretion, this polymer sticks to virtually any surface.

What makes it even more interesting is that a second layer of just about any other coating can be applied on top of the polymer and, in most cases, stick.

These secondary coatings can be anything from a thin metal layer on electronic circuitry to surfaces that promote stem cell growth to coatings that prevent bacteria from attaching to medical implants or prevent barnacles from adhering to ship hauls.

In the past, it has been difficult getting these secondary coatings to stick directly to certain surfaces, including Teflon or silicone. But Messersmith’s polymer acts sort of like a primer between any surface and any coating.

"The real strength of their invention and insight comes out of the fact that dopamine is a very reactive molecule. There are all kinds of things they can attach to that polymer film," said Herbert Waite a professor in the department of molecular, cellular and developmental biology at the University of California, Santa Barbara.

But Waite also argues that while the mussel adheres well underwater, the dopamine does not. This could make it difficult in biomedical applications.

"I don’t think you’d get away with treating an implant surface with dopamine," said Waite. "Many of the limitations on true adhesion…rely on the clinician ultimately doing things in a wet environment. The dopamine doesn’t address the clinical need of working in a wet patient environment."

Messersmith acknowledged the limitations surrounding medical applications.

"It’s very challenging to do all of the studies to prove safety and efficacy. What we tried to do here is establish a concept that, with further development, could be useful for the things we mention," he said.

But an even more fundamental question, said Waite, is why is the dopamine molecule so sticky in the first place?

"That’s a huge question that a lot of people would like to know the answer to, including me," said Messersmith.

Via: Discovery Channel


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