Sandcastle worm inspired undersea adhesives
Résumé de la communication de Russell STEWART (University of Utah, USA) donnée à l’occasion du séminaire Les constructions en milieu marin / Constructions in marine environment du 14 au 19 mars 2016
Reef-building sandcastle worms, and related Sabellariidae polycheates, use underwater glue on a massive scale to geoengineer the world’s coastlines. Individual worms meticulously construct tubular shells around their bodies by gluing together sandgrains or shell fragments captured with ciliated tentacles from the turbulent intertidal water column. In response to specific cues, sandcastle worm larva initiate construction of new tubes on existing tubes, thus enlarging the honeycomb-like reefs. The sandcastle worm glue is a multipart, granulated, self-initiating underwater adhesive. The sandcastle glue is preorganized, packaged, and stored at very high concentration, in two types of granules, as condensed pairs of oppositely charged macromolecules and/or divalent metal ions. The two types of pre-organized adhesive packets are secreted separately and intact through the surface of the building organ. The granules are ruptured and transition into a complex fluid morphology. The fluid hardens, or sets, in response to changes in the environmental conditions, such as pH, ionic strength, and ionic composition, when exposed to seawater. The final glue has a solid foamy morphology. A latent catechol oxidase enzyme (curing agent) that is copackaged with the other adhesive components into both types of adhesive packets catalyzes covalent crosslinking. The curing becomes a structural component of the glue. The final glue has the stiff but flexible consistency of shoe leather.
To create synthetic sandcastle glue mimetic adhesives four features of the natural glue were copied with synthetic polymers: the chemical nature of the adhesive components (oppositely charged polyelectrolytes, the material form of the adhesive (liquid complex coacervates), the transition of the liquid form into a solid gel form (the environmentally triggered setting reaction), and the post-set hardening reaction (covalent crosslinking of the components).
The biomimetic adhesive is in pre-clinical testing for sealing fetal membranes after in utero surgery, and as a water-borne liquid embolic for controlling blood flow.