Environmental post-processing increases the adhesion strength of mussel byssus adhesive

Marine mussels (Mytilus trossulus) attach to a wide variety of surfaces underwater using a protein adhesive that is cured by the surrounding seawater environment. In this study, the influence of environmental post-processing on adhesion strength was investigated by aging adhesive plaques in a range of seawater pH conditions. Plaques took 8–12 days to achieve full strength at pH 8, nearly doubling in adhesion strength (+94%) and increasing the work required to dislodge (+59%). Holding plaques in low pH conditions prevented strengthening, causing the material to tear more frequently under tension. The timescale of strengthening is consistent with the conversion of DOPA to DOPA-quinone, a pH dependent process that promotes cross-linking between adhesive proteins. The precise arrangement of DOPA containing proteins away from the adhesive-substratum interface emphasizes the role that structural organization can have on function, an insight that could lead to the design of better synthetic adhesives and metal-coordinating hydrogels.