Availability of Environmental Iron Influences the Performance of Biological Adhesives Produced by Blue Mussels.

Animals incorporate metals within the materials they manufacture, such as protective armor and teeth. Iron is an element used for adding strength and self-healing properties to load-bearing materials. Incorporation of iron is found beyond hard, brittle materials, even within the soft adhesive produced by marine mussels. Such findings suggest that the bioavailability of iron may have an influence on the properties of a biological material. Experiments were conducted using live mussels in which seawater iron levels were deficient, normal, or in excess of typical concentrations. The weakest adhesive strengths were produced in iron-deficient waters. Increasing seawater iron brought about more robust bonding. Changes in strengths correlated with varied adhesive morphology, color, and microstructural features, likely a result of variations in the degree of iron-induced protein cross-linking. This study provides the first whole animal scale data on how the manipulation of bioavailable iron influences the performance of a biological material. Changing ocean chemistries will alter the iron bioavailability when a decrease in pH shifts elemental speciation from particulate to dissolved, hindering the ability of filtering organisms to capture nutrients. These results show future implications of changing ocean chemistry as well as of the resulting abilities of marine organisms to construct essential materials.

Examining Potential Active Tempering of Adhesive Curing by Marine Mussels.

Mussels generate adhesives for staying in place when faced with waves and turbulence of the intertidal zone. Their byssal attachment assembly consists of adhesive plaques connected to the animal by threads. We have noticed that, every now and then, the animals tug on their plaque and threads. This observation had us wondering if the mussels temper or otherwise control catechol chemistry within the byssus in order to manage mechanical properties of the materials. Here, we carried out a study in which the adhesion properties of mussel plaques were compared when left attached to the animals versus detached and exposed only to an aquarium environment. For the most part, detachment from the animal had almost no influence on the mechanical properties on low-energy surfaces. There was a slight, yet significant difference observed with attached versus detached adhesive properties on high energy surfaces. There were significant differences in the area of adhesive deposited by the mussels on a low- versus a high-energy surface. Mussel adhesive plaques appear to be unlike, for example, spider silk, for which pulling on the material is needed for assembly of proteinaceous fibers to manage properties.