Plant-Based Underwater Adhesives Developed for Bonding Coral in Sea Water

Many commercial adhesives are derived from petroleum, cannot degrade, and are unable to bond in wet environments. Adhesive materials are needed for applications ranging from bonding biomedical devices to repairing coral reefs. With changing ocean chemistry, corals are bleaching. Efforts to plant heat- and acid-tolerant species are hampered by the lack of viable underwater glues. Experiments described herein are working toward making biobased adhesives that create strong bonds underwater. The base system is made from zein, a protein from corn, cross-linked with tannic acid. Inorganic materials were added to generate the particularly strong underwater adhesives. Structure–function studies showed that inorganic components such as layered silicate and calcium carbonate increased the bond strengths significantly. Viscosity studies demonstrated shear thinning properties that are critical for adhesive applications. Mixed adhesive and cohesive failure modes indicated that bonding to the substrate surfaces and cohesion within the bulk material could be balanced well. Adhesion was measured on time frames as short as 10 min and as long as 9 weeks. These materials were then used for the attachment of coral skeletons to substrates. The resulting underwater adhesives can be made on large scales, are easy to handle, bond strongly, and may provide a path to enabling more widespread planting of corals.