Sticking point: researchers turn to shellfish for a strong bond

Researchers in the US have turned to nature to develop an adhesive that works under water and is stronger than a number of commercially available glues.

The team at Purdue University in Indiana modelled their biomimetic polymer on compounds found in shellfish.

“Our current adhesives are terrible at wet bonding, yet marine biology solved this problem eons ago,” said Jonathan Wilker, a professor of chemistry and materials engineering at Purdue University.

“Mussels, barnacles, and oysters attach to rocks with apparent ease. In order to develop new materials able to bind within harsh environments, we made a biomimetic polymer that is modelled after the adhesive proteins of mussels.”

Results showed that the bio-based glue performed better than 10 commercial adhesives when used to bond polished aluminium.

Compared with the five strongest commercial glues included in the study, the new adhesive performed better when bonding wood, Teflon and polished aluminium. It was the only adhesive of those tested that worked with wood and out-performed the other adhesives when used to join Teflon.

Findings are detailed in a research paper published online and in ACS Applied Materials and Interfaces.

Mussels extend hair-like fibres that attach to surfaces using plaques of adhesive. Proteins in the glue contain DOPA (dihydroxyphenyalanine), an amino acid that harbours the chemistry needed to provide strength and adhesion.

Purdue researchers have now inserted this chemistry of mussel proteins into a biomimetic polymer – poly(catechol-styrene) – creating an adhesive by harnessing catechols, which are have the same functional chemical groups as those found in DOPA.

“We are focusing on catechols given that the animals use this type of chemistry so successfully,” Wilker said in a statement. “Poly(catechol-styrene) is looking to be, possibly, one of the strongest underwater adhesives found to date.”

While most adhesives interact with water instead of sticking to surfaces, the catechol groups may have a special talent for “drilling down” through surface waters in order to bind onto surfaces, he said.

The series of underwater bond tests were performed in tanks of artificial seawater.

“These findings are helping to reveal which aspects of mussel adhesion are most important when managing attachment within their wet and salty environment,” Wilker said. “All that is needed for high strength bonding underwater appears to be a catechol-containing polymer.”

Future research will include work to test the adhesive under real-world conditions.

The paper – High Strength Underwater Bonding with Polymer Mimics of Mussel Adhesive Proteins – can be found here.