Mucus-derived proteins (mucins) and mucin-inspired polymers can be transformed into sticky gels through a crosslinking strategy inspired by the adhesion of marine mussels. [Image courtesy of the researchers at MIT and Freie Universität Berlin]
A paper detailing the team’s results appeared in February in the Proceedings of the National Academy of Sciences. The MIT authors included George Degen, Corey Stevens, Gerardo Cárcamo-Oyarce, Jake Song, Katharina Ribbeck, and Gareth McKinley, along with Raju Bej, Peng Tang, and Rainer Haag of Freie Universität Berlin. The U.S. National Institutes of Health, the U.S. National Science Foundation, and the U.S. Army Research Office helped fund the research.
“The applications of our materials design approach will depend on the specific precursor materials,” George Degen, a postdoc in MIT’s Department of Mechanical Engineering, said in an MIT news release.
“For example, mucus-derived or mucus-inspired materials might be used as multifunctional biomedical adhesives that also prevent infections. Alternatively, applying our approach to keratin might enable the development of sustainable packaging materials.”
The research group focused on a chemical motif that appears in mussel adhesives: a bond between two chemical groups known as “catechols” and “thiols.” In the mussel’s natural glue, or plaque, these groups combine to form catechol–thiol cross-links, and that’s what enables the cohesive strength of the plaque. In addition, the catechols enhance a mussel’s adhesion, binding to surfaces such as rocks and ship hulls.
Thiol groups are also prevalent in mucin proteins, which are the primary non-water component of human mucus. Degen and his colleagues wondered whether mussel-inspired polymers could link with mucin thiols, enabling the mucins to quickly turn from a liquid to a sticky gel.
To test the concept, they combined solutions of natural mucin proteins with synthetic mussel-inspired polymers and observed how the resulting mixture solidified and adhered to surfaces over time.
“It’s like a two-part epoxy. You combine two liquids together, and chemistry starts to occur so that the liquid solidifies while the substance is simultaneously gluing itself to the surface,” Degen said.
Added Degan’s colleague Rainer Haag at Freie Universität Berlin: “Depending on how much cross-linking you have, we can control the speed at which the liquids gelate and adhere. We can do this all on wet surfaces, at room temperature, and under very mild conditions. This is what is quite unique.”
The team deposited a range of compositions between two surfaces and found that the resulting adhesive held the surfaces together, with forces comparable to the commercial medical adhesives used for bonding tissue. In addition, they tested the adhesive’s bacteria-blocking properties by depositing it onto glass surfaces and incubating the glass with bacteria overnight.
“We found if we had a bare glass surface without our coating, the bacteria formed a thick biofilm, whereas with our coating, biofilms were largely prevented,” Degen said.
The research team concluded in their paper abstract: “The results highlight the potential of catechol–thiol cross-linking as a versatile platform for engineering multifunctional glycoprotein hydrogels with applications in wound repair and antimicrobial surface engineering.”
The team says that with some fine-tuning, they can further enhance the adhesive’s hold. The result could be a strong and protective alternative to existing medical adhesives.
“We are excited to have established a biomaterials design platform that gives us these desirable properties of gelation and adhesion, and as a starting point we’ve demonstrated some key biomedical applications,” Degen said. “We are now ready to expand into different synthetic and natural systems and target different applications.”
