Sandcastle worms teach us how to make underwater glue

A sandcastle worm (Phragmatopoma californica) making a tube out of sand (yellow) and beads of zirconium oxide (white). (Credit: Fred Hayes)

Researchers are designing a new synthetic wet glue that mimics an adhesive secreted by the sandcastle worm (Phragmatopoma californica), a marine invertebrate commonly found along the California coast.

The animals use the adhesive to build hive-like shelters in colonies.

A colony of sandcastle worm tubes
A colony of sandcastle worm tubes. (Credit: Fred Hayes)

“Sandcastle worms secrete a robust underwater adhesive to build a tube reef (sandcastle) in harsh intertidal environments, where wind and wave velocity often exceed 25 meters per second,” says Kollbe Ahn, a research faculty member at UC Santa Barbara’s Marine Science Institute and co-lead author of a paper in Nature Materials. “We successfully replicated the strong wet-contact adhesion of the bio-adhesion featuring nanoscopic chemical and miroscopic porous structures.”

While wet glues have been the subject of research and development for years, they have yet to approach the performance of the natural substances in terms of stickiness and the rapidity with which the adhesion process occurs. In fact, synthetic underwater adhesives have typically required complex processing and functionalization, adding several steps to what would ideally be a simple process.

“From practical perspectives, simple processing saves time and labor, and ultimately reduces costs,” says materials scientist and lead author Qiang Zhao. The new glue is particularly noteworthy, he says, because through a phenomenons called solvent exchange, adhesion becomes a little more streamlined.

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“The processing of this wet glue does not need pre-immersive dry curing or applied compressing pressure that are normally required in conventional studies,” Zhao says. The synthetic glue also promotes adhesion between a variety of surfaces, including plastics, glasses, metals, wood, and biological tissues.

Additionally, the resulting microarchitecture of the synthetic glue, which mimics the porous structure of sandcastle worm adhesive, makes it more resistant to cracking.

“Porous structures, or cellular structures, are ubiquitous in nature, such as in cork, bones, and coral, and they are found to increase fracture energy of these materials,” Zhao says. “Here in the context of wet adhesion, we found that the porosity was reminiscent of the porous structures of sandcastle worm cement, and significantly improved wet adhesion.”

The researchers say the ultimate goal is to create a wet glue that can be used in a variety of applications, such as dental adhesion and to repair tissue, skin, bones and membranes that are surrounded by bodily fluids.

Source: UC Santa Barbara