Mussels can glom onto just about any surface--even Teflon. What’s more, the glues they use adhere in water, making them ideal candidates for biomedical applications such as suturing skin and setting broken bones. A new study sheds light on the bivalves' sticky secret, identifying a key adhesive compound.
Researchers had long speculated that an amino acid called DOPA, found in high concentrations in mussel proteins, was responsible for the special adhesive qualities of mussel glue. But they lacked proof that DOPA had the right kind of chemistry to adhere to other materials.
To investigate, Phil Messersmith, a biomedical engineer at Northwestern University in Evanston, Illinois, and colleagues tethered a single molecule of DOPA to the tip of an atomic force microscope. They then touched the tip to a titanium dioxide surface and measured the force needed to pull the DOPA off the surface. It took a remarkable 800 piconewtons to do the trick, almost 4 times more than the force necessary to pull apart a pair of joined avidin and biotin molecules, the strongest known link in biology that doesn't involve sharing electrons between atoms. Such covalent bonds are part of DOPA's repertoire, however. The compound formed covalent bonds to organic surfaces such as an amine-coated silicon wafer, the researchers report online this week in the Proceedings of the National Academy of Sciences.
Unlike covalent bonds, the DOPA-oxide bond can reform if it comes undone in water, the researchers found. That property might make the compound useful in biomedical devices, Messersmith says. He's now investigating using DOPA to anchor a nonstick polymer onto various surfaces, including ceramic and metal, creating nonadhesive surfaces. If applied as a coating to metal implants such as stents, heart valves, or other devices, they might prevent blood cells and proteins from accumulating. Messersmith has established a start-up company, Nerites Corp., to develop such glues.
The study explains how mussels can adhere to virtually any surface, even in water, says Herbert Waite, a marine biochemist at the University of California at Santa Barbara. "Water or other aqueous solutions can create problems for all kinds of adhesion," he says. The study shows how the mussel gets around this using DOPA to create different types of bonds.