Biomimetic Underwater Adhesives with Environmentally Triggered Setting Mechanisms

Abstract

The challenges of developing medical adhesives for the wet environment of open surgery are analogous to the adhesion problems solved by marine organisms living at the watery interface of land and ocean. These organisms routinely bond dissimilar materials together under seawater with little if any surface preparation. One such organism is the sandcastle worm (Phragmatopoma californica). Our goal is to copy this marine worm’s mechanisms of underwater bonding to create synthetic water-borne underwater medical adhesives, and in turn, to use the synthetic adhesives to test mechanistic hypotheses about the natural adhesive. Biomimetic underwater adhesives were formulated with polyelectrolytic analogues of the natural glue proteins. The copolymers condensed into complex coacervates—dense partially water-immiscible cohesive fluids poised between soluble polymers and insoluble polymeric salts. The boundary between fluid coacervate phases and solid or gelled states was dependent on divalent cation species as well as the pH and temperature, which demonstrated that these environmental factors can trigger the adhesive setting reaction (Fig. 1). The results provide, respectively, empirical support for the natural pH-triggered set hypothesis and practical triggers for controlled setting of mimetic medical adhesives.