The key ingredient of the superglue that mussels use to attach themselves to rocks, boats and piers is iron, scientists say. The finding, described in the latest issue of the journal Angewandte Chemie International Edition, represents a novel biological use for the metal.
Jonathan Wilker of Purdue University started investigating the stickiness of mussels and barnacles after a scuba diving trip. Saltwater mussels attach to objects using a number of filaments (see image). The creature extends its foot and affixes the tiny fibers with glue. In the new work, Wilker and his colleagues identified iron as the necessary ingredient in the adhesive. "The mixture we extract from mussels has a consistency similar to gelatin," Wilker says. "When we add iron, the mussel proteins cross-link or 'cure' and the material hardens. Other bioavailable metal ions do not appear to bring about this cross-linking." Iron, which is present in seawater, is readily available to the bivalves. "Proteins often rely on metal ions to tie them together and provide stability, but this is the first time that a transition metal ion has been determined to be an integral part of a biological material," notes chemist Mike Clarke of the National Science Foundation.
The mussel glue sticks to a broad variety of materials, including TeflonTM, which is widely used as a nonstick coating. "The biological origin of this glue and the ability to stick to nearly all surfaces invite applications such as the development of surgical adhesives," Wilker remarks. In addition, understanding just how these creatures stick may help researchers devise novel methods to protect ships from unwanted passengers. "Understanding how marine glues are formed could be key to developing surfaces and coatings to prevent adhesion processes," Wilker says. "Current antifouling paints rely upon releasing copper into surrounding waters, thereby killing barnacles in their larval state. We are hoping our results will help make antifouling paints that do not require the release of toxins into the marine environment."