McCormick

Fall 2013 Magazine

Data as Art

Sticky When Wet

Why biomedical engineer Phillip Messersmith thinks some of our favorite foods hold the key to safer surgery

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Phillip Messersmith (left) and graduate student Tadas SileikaMussels, red wine, chocolate, tea: the sources of Phillip Messersmith’s inspiration sound more like a dinner menu than the spark for medical breakthroughs. But for nearly a decade, these foods’ properties have aided Messersmith in his development of adhesive surface coatings that could improve surgery and save lives.

“Nature has created materials that can easily do what manmade materials cannot: adhere to wet surfaces,” says Messersmith, Erastus Otis Haven Professor of Biomedical Engineering and of Materials Science and Engineering. “Our goal is to understand biological adhesives so we can mimic what nature does so well.”

Top on Messersmith’s list is developing a nontoxic antibacterial coating to help prevent device-related infections. Bacteria tend to attack medical devices when they are placed in the human body, sometimes causing life-threatening reactions; while fluid-based bacteria are relatively easy for immune systems to fight, surfaces provide a place for the microorganisms to assemble themselves into colonies called biofilms, which can resist the body’s defenses and antibacterial drugs. Antibacterial coatings on medical devices like catheters and pacemakers could stave off infection, but they would have to be able to adhere to those devices inside the body’s wet environment—a challenge for most synthetic adhesives, which deteriorate or fail in the presence of moisture. New synthetic adhesives could also be used to attach or repair tissues in surgery.

Messersmith uses food products such as mussels, red wine, chocolate, and tea in order to produce adhesive surface coatings.As Messersmith found, mussels can offer at least part of the solution. The bivalves can adhere to virtually all inorganic and organic surfaces underwater and even in turbulent tides, thanks to a special glue secreted from their tongue-like “foot.” The glue is secreted as a liquid but hardens rapidly into a solid, water-resistant adhesive that can stick to minerals, metals, wood, and other surfaces. Key to the glue’s stickiness are mussel adhesive proteins, a family of unique proteins containing a high concentration of the catecholic amino acid DOPA (dihydroxyphenylalanine).

Messersmith noticed that dopamine—commonly known as a neurotransmitter—shared the mussel proteins’ essential elements. (Both have chemical structures with two hydroxyl groups, the segment of the molecule believed to provide adhesive qualities.) In his lab he re-created the mussel proteins’ adhesive function in a few simple steps, dissolving a small amount of dopamine in a beaker of water and adjusting the water’s acidity to match that of seawater. He then placed a solid object in the solution; several hours later, the object was coated with a thin polydopamine film less than 100 nanometers thick.

The polydopamine coating was not antibiotic, but it provided a surface with high chemical reactivity, a feature that could be useful not only for medical devices but also for manufacturing and industrial uses. “We can take advantage of that reactivity to apply the second layer,” says Messersmith. “For example, I could place an iPod casing in the dopamine solution, and a thin polydopamine coating would form. Then I could take it out and put it in a metal salt solution and form a coating of copper or silver.” The same technique could be used to coat medical polymers in silver, which has excellent antimicrobial properties. Messersmith’s group went on to develop a number of coatings that anchor onto surfaces using the same chemical interactions found in mussel adhesive proteins.

Medical polymers shown with various combinations of Messersmith's plant-derived coating and other antibacterial substances.Recently Messersmith made another connection: he noticed that the chemical compositions of polyphenols—a large and diverse family of chemicals, common in plant tissues, that are often touted for their antioxidant properties—were very similar to those of mussel adhesive proteins. In plants, polyphenols have a wide range of purposes, such as camouflaging leaves and making them taste bitter, but one characteristic is especially appealing. “Plant-derived polyphenols are often intrinsically antibacterial,” says Messersmith. “If we could perfect a polyphenol adhesive, it could be extremely valuable for surgical applications.”

A simple experiment demonstrated how a plant-derived coating could work. Messersmith poured wine into a clean glass and let it sit for several hours in his kitchen sink, then poured out the wine and rinsed the glass so it appeared clean. When he added a colorant, however, a thin coating of polyphenols was revealed on the glass. Bacteria died when introduced to the coating.

“What’s interesting is that the raw materials we regularly encounter in our diets can benefit us in a way we had never envisioned,” says Tadas S. Sileika, a graduate student in Messersmith’s lab who worked on the polyphenol coating. “The coatings have innate properties that can help save lives and keep people healthy. Without any further modification, they can help prolong the life of a medical device, reduce inflammation in a patient’s body, and prevent bacterial infections.”

Another variety of medical polymer used for a surface for the antibacterial coatings.Based on this knowledge, Messersmith developed a method that could produce the coating more effectively. He found that immersing objects in a saline solution of tannic acid results in the same coating in less time. His team tested all kinds of materials—medically relevant polymers, engineering polymers, metals, inorganic substrates, and ceramics—and the coating stuck to each one. The coating could also be modified to take on additional characteristics, such as stronger antibacterial properties.

The plant-based adhesive has other benefits. Unlike the brown coloring of the mussel-inspired coating, the polyphenol coating is colorless, which is preferred for many manufacturing applications.The compounds used in producing the plant-based coating are also 100 times less expensive.

In 2004 Messersmith founded Nerites, a company to commercialize his polydopamine coating; he has since sold the company, but it continues to work toward getting the surgical adhesives into operating rooms. In addition to his mussel-based adhesive research, Messersmith is developing plant-based adhesives to make surfaces attract or repel water, technology that could be used to manufacture nonwetting or self-cleaning surfaces.

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By: Sarah Ostman