Sticky dopamine

A mussel clinging to a sheet of teflon. (Image credit: Haeshin Lee/ Phillip Messersmith)

The marine mollusc Mytilus edulis inhabits ecological niches in the intertidal zone, which is exposed to air during low tide and submerged in water during high tide. Being so turbulent, these niches are inhospitable to many forms of life; the organisms that do inhabit such harsh conditions are suitably adapted, and the success of the mussel is due largely to its ability to adhere to virtually any kind of surface.

The mussel's steadfast grip is achieved by means of collagenous threads consisting of a glue protein called Mefp-5, which is secreted by exocrine glands in the foot. Last year, a team of researchers led by Phillip Messersmith of Northwestern University in Evanston, Illinois, determined that the major component of the mussel's glue protein is an amino acid called 3,4-dihydro-L-phenylalinine, the precursor of the neurotransmitter dopamine.

Now, writing in the journal Science, Messersmith's team reports that they have used dopamine itself to form a highly adhesive glue that has many potential applications.

Messersmith and his colleagues first added dopamine to water that had the same pH (acidity) as seawater. In these conditions, the dopamine molecules bind to each other end-to-end to form chain-like molecules. (These chains are  polymers of dopamine, hence the solution is called polydopmaine.)

Immersion of objects in the solution resulted in the deposition of a thin, adherent polydopamine film on the object's surface. And just as the glue protein synthesized by mussels can adhere to almost any surface (organic and inorganic, wet or dry), so the polydopamine solution adhered to every surface on which it was tested.

The solution was also used to coat objects with a wide variety of materials. For example, metal coins, plastics, glass and various metals immersed first in polydopamine could then be dip-coated with silver nitrate and copper chloride, which formed films of uniform thickness. 

Furthermore, the polydopamine coating deposited onto surfaces could be patterned using photolithography. The ability to pattern adhseive surfaces in this way has many potential applications. For example, the researchers made a surface on which a specific ligand-receptor interaction could take place. By choosing the appropriate coatings, surfaces which inhibit or promote specific biomolecular interactions could easily be formed.

The aim of Messersmith's group is to develop biologicall-inspired materials for the repair and replacement of human tissues. But the dopamine-based glue has many potenital applications, including the formation copper nitrate-coated sheets for use in flexible displays and the cleaning of water polluted with heavy metals such as mercury or lead. 

References:

Lee, H., et al. (2007). Mussel-inspired surface chemistry for multifunctional coatings. Science 318: 426-430. [Abstract]

Lee, H., et al. (2006). Single-molecule mechanics of mussel adhesion. Proc. Natl. Acad. Sci. 103: 12999-13003. [Full text]