In Situ Deactivation of Catechol-Containing Adhesive Using Electrochemistry.

Marine mussels secret catechol-containing adhesive proteins that enable these organisms to bind to various surfaces underwater. Synthetic mimics of these proteins have been created to function as adhesives and coatings for a wide range of applications. Here, we demonstrated the use of in situ electrical field stimulation to deactivate the adhesive property of catechol-containing adhesive that is in direct contact with a surface. Johnson-Kendall-Roberts (JKR) contact mechanics test was performed using a titanium (Ti) sphere in the presence of a pH 7.5 aqueous buffer. The Ti sphere also served as a conductive electrode for applying electricity to the adhesive, while a platinum (Pt) wire served as the counter electrode. Work of adhesion (Wadh) decreased with increased levels of applied voltage and current, exposure time to the applied electricity, and salt concentration of the interfacial buffer. Application of 9 V for 1 min completely deactivated the adhesive. UV-vis diffuse reflectance spectra and tracking of catechol oxidation byproduct, hydrogen peroxide, confirmed that catechol was oxidized as a result of applied electricity. Contact mechanics testing further confirmed that the Young's modulus of the adhesive increased by nearly 4 folds at the interface as a result of oxidative cross-linking, even though the modulus of the bulk of the adhesive was unaffected by applied electricity. The accumulation of hydroxyl ions near the cathode increased the local solution pH, which promoted oxidation-induced cross-linking of catechol and subsequently decreased its adhesive property. Tuning adhesive properties through in situ electrochemical oxidation provides on-demand control over the adhesive, which will potentially add another dimension in designing synthetic mimics of mussel adhesive proteins.