Mussels secrete a protein that helps them stick to underwater surfaces like rock, metal, or wood. Chemists have designed sticky polymers that mimic this protein, but these materials quickly set when exposed to air. To get more control with these adhesives, researchers from Japan have developed a mussel-mimicking polymer that sets only when hit by light (ACS Macro Lett., DOI: 10.1021/mz300524q). The polymer could be used as an adhesive for biomedical devices such as stents, the researchers say.
Mussel adhesion proteins are sticky because of an unnatural amino acid called 3,4-dihydroxy-L-phenylalanine, or L-DOPA. Oxygen in seawater oxidizes the catechol side chain of this amino acid, producing a benzoquinone group. Then lysines in the protein can attack the benzoquinone, connecting protein chains and forming a gel that attaches the bivalve to a surface.
Because catechol groups oxidize quickly, synthetic polymers that mimic the mussel proteins form a gel within minutes of being exposed to air. Atsushi Takahara, at Kyushu University, and his colleagues wanted to control the timing of gel formation. So they synthesized an acrylamide polymer containing catechols protected by o-nitrobenzyl groups to prevent oxidation. When hit with light, these nitrobenzyl groups cleave themselves off the catechol groups, allowing the polymer to be oxidized.
The new polymer set within 30 minutes after exposed to high-intensity visible light from a mercury-xenon lamp. To test the polymer’s adhesive strength, the team sandwiched the material between two glass plates, triggered gel formation with light, and then tried to pull the glass plates apart. The shear strength of the glue was similar to that of other commercial medical adhesives, such as ones used to seal cuts (Mater. Sci. Eng. C, DOI: 10.1016/j.msec.2005.03.006).