To develop the new adhesive, the researchers studied the chemical components of a protein in mussel glue, identifying important functional chemical groups. In earlier work, they’d made a glue based on one of these groups. (See “Nanoglue Sticks Underwater.”) But the resulting glue worked only with inorganic materials and was difficult to make. The new adhesive contains two chemical groups found in mussel glue, rather than just one. The combination allows the adhesive to bind to both organic and inorganic materials. What’s more, the new adhesive is readily available. The researchers noted that the two chemical groups, amines and catechols, are found in dopamine, a compound best known as a neurotransmitter. At the right pH level, dopamine self-assembles into polymer chains to produce thin films of the adhesive. It’s also sold commercially, and it’s inexpensive.
The adhesive, which is described in the current issue of Science, is already attracting the interest of other researchers. For example, Nicholas Kotov, a professor of chemical engineering at the University of Michigan, intends to use it to make thermoelectric materials–materials that convert heat directly into electricity. Such materials must conduct electricity well but heat badly. Kotov says that it may be possible to use the adhesive to bind together electrically conductive materials such as carbon nanotubes. The adhesive itself could serve as a thermally insulating layer, he says.
Another researcher, Herbert Waite, a professor of molecular, cellular, and developmental biology at the University of California, Santa Barbara, calls Messersmith’s work very interesting. But he notes some limitations that could be exceeded through further study of the mussel that served as the adhesive’s inspiration. Messersmith’s adhesive can be applied only under conditions in which concentrations of the dopamine and pH levels are strictly maintained. Ideally, Waite says, it would be nice to have a glue that, like the mussel’s, can be applied to any substrate, even in water, without external control of environmental parameters.