Lower Critical Solution Temperature-Driven Self-Coacervation of Nonionic Polyester Underwater Adhesives

To enable attachment to underwater surfaces, aquatic fauna such as mussels and sandcastle worms utilize the advantages of coacervation to deliver concentrated protein-rich adhesive cocktails in an aqueous environment onto underwater surfaces. Recently, a mussel adhesive protein Mfp-3s, was shown to exhibit a coacervation-based adhesion mechanism. Current synthetic strategies to mimic Mfp-3s often involve complexation of oppositely charged polymers. Such complex coacervates are more sensitive to changes in pH and salt, thereby limiting their utility to narrow ranges of pH and ionic strength. In this study, by taking advantage of the lower critical solution temperature-driven coacervation, we have created mussel foot protein-inspired, tropoelastin-like, bioabsorbable, nonionic, self-coacervating polyesters for the delivery of photo-cross-linkable adhesives underwater and to overcome the challenges of adhesion in wet or underwater environments. We describe the rationale for their design and the underwater adhesive properties of these nonionic adhesives. Compared to previously reported coacervate adhesives, these "charge-free" polyesters coacervate in wide ranges of pH (3-12) and ionic strength (0-1 M NaCl) and rapidly (<300 s) adhere to substrates submerged underwater. The study introduces smart materials that mimic the self-coacervation and environmental stability of Mfp-3s and demonstrate the potential for biological adhesive applications where high water content, salts, and pH changes can be expected.