Bio-Inspired Strong Underwater Nano Adhesives

Santa Barbara, CA, October 26, 2015 (Newswire.com) - ​The marine mussels use strong filaments to adhere to rocks in the inter-tidal zones of the wave swept beaches, preventing them from being swept away in strong sea currents. Researchers from the University of California Santa Barbara borrowed and simplified chemistries that the mussel foot uses to overcome this engineering challenge of wet adhesion to create a one component adhesive system, which holds potential for employment in nanofabrication protocols. They synthesized and characterized the strongest reported underwater nano adhesive till date.

Their findings appear online in the journal Nature Communications (http://www.nature.com/ncomms/2015/151019/ncomms9663/full/ncomms9663.html).

Presence of water limits the ability of an adhesive to stick to surfaces under wet conditions. However, a protein secreted by mussels has the ability to penetrate the superficial water layer and adhere to the underlying surface. These proteins are rich in catechol content and features prominently ranging from less than 5 mol% to 30 mol%. Other common naturally occurring amino acids, for example, lysine, phosphoserine and histidine, are also relevant to protein adhesion, however, the role of these other residues is still an enigma in the wet adhesion community. Catechol is often thought to be the magic bullet behind the strong wet adhesive properties of the proteins underwater.

The researchers from UC Santa Barbara translated the strong wet adhesion of the mussel proteins into a smaller and simpler zwitterionic platform. They simplified and combined several motifs borrowed from the interfacial adhesive mussel proteins (including catechol, positive and negative charges, and nonpolar residues) into a single, low-molecular-weight, one-component adhesive system. Their study underscores the importance of catechols and of maintaining a balance between hydrophobic and electrostatic interactions for tuning or optimizing both coacervation, a property essential for the nano adhesive to spread onto the target surface without getting dissolved in water, and adhesion. 

The adhesion energies measured (Wad~50 mJ m−2) in the study is the highest reported to date for a nanometer-thick film (a billionth of a meter) formed underwater, and 2–3 times greater than the strongest adhesive mussel foot protein. The findings also describes the design principles for engineering synthetic molecules that will contribute to the development of tunable systems for applications in protective coatings, medical adhesives and, drug delivery. 

Such novel zwitterion-mediated adhesion is likely to stimulate applications at multiple length scales including nanofabrications that require molecularly smooth and thin (<4 nm) adhesive layers, for example, in electronic, Lithium-ion battery and biomedical applications.

This research was a collaborative effort between Chemical Engineering, Marine Science Institute and Chemistry and Biochemistry departments at the University of California Santa Barbara. Dr. B. Kollbe Ahn and Dr. Saurabh Das co-lead the project and ideas for the designing and testing of the novel molecules used in this study.