Biomimetic Block Polycatechols Form High Strength Wet Adhesives

Marine organisms such as mussels and sandcastle worms secrete glue proteins that enable robust wet adhesion on diverse substrates. The adhesive attributes of these proteins have been ascribed to catecholic 3,4-dihydroxy-L-phenylalanine (DOPA) moieties. Correspondingly, numerous attempts have sought to imbue synthetic and bioderived polymers with wet adhesion characteristics by incorporating catechol groups. However, current catechol-containing wet adhesive technologies suffer from poor adhesion due to their lack of control over the content and location of catechol groups in the polymer backbones. In this work, we address these limitations by designing and synthesizing block polycatechols with a controlled, high-density placement of catechol groups. Aqueous solutions of these block polycatechols exhibit exceptionally strong bonding with diverse organic and inorganic surfaces, with failure strengths exceeding 1 MPa on collagen and plastics, >13 MPa on metals such as aluminum, steel, and zinc, and >15 MPa on glass, far outperforming typical medical and industrial adhesives. Moreover, using a library of block copolymers, we establish that the adhesive performance of these block polycatechols can be systematically tuned by varying the catechol block length, bridging polymer length, and the catechol oxidation state by modulating the extent and strength of the cohesive and the interfacial bonds. Optical photo-thermal infrared spectroscopy on polymer-coated substrates sheds light on the interfacial adhesive mechanisms between catechol groups and surfaces, highlighting the influence of oxidation state and catechol density on strengthening interfacial adhesion. Through chemical and macromolecular engineering of block copolymers, this work establishes design rules for making biomimetic hydrogels that exhibit robust adhesion to diverse surfaces.