Blue mussels (Mytilus edulis) are bivalves that attach to rocks in wave-battered intertidal seashores. They attach using stringy fibers that emerge from their protective shells, secreted by glands on the soft bodies inside. These fibers, called byssal threads, stick to the rock with a mussel-produced adhesive comparable in strength to human-made glues but without carcinogens, such as formaldehyde. The mussel glue can also cure under water.
A key feature of the blue mussel’s unique adhesive chemistry is the presence of the amino acid 3,4-dihydroxyphenylalanine, with its reactive catechol functional group (two hydroxyl groups sticking out from a benzene ring) that forms strong bonds with catechols on adjacent molecules and with metal atoms present in the surface of most natural solid substrates. Another key feature is the ability of catechol chains to overcome a solid surface’s otherwise strong preference for water molecules (which is why conventional adhesives fail on wet surfaces).
New mussel-inspired adhesives, which have wide-ranging applications from surgical glues to wood composites, currently use soy as an inexpensive, accessible feedstock. These human-made adhesives work by blocking certain amino acids in soy proteins that are not present in mussel proteins, such as glutamic acid, so that the resulting compound bears a closer resemblance to that of mussel proteins.
“Pounding waves are no match for the mighty mussel, that produces strong, flexible threads that cling to rocks…mussels secrete a unique amino acid called dihydroxyphenylalanine…Researchers have developed a new group of adhesives for wood products inspired by the ability of mussels to cling to rocks using thread-like tentacles. These threads are proteins that retain powerful adhesive properties even in water.” (ScienceDaily 2005)