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Thursday, 01 October 2020

Inspired by mussels, barnacles and yummy oysters

Wednesday, 3 September 2014 | Posted by: Michael Richter, European Coatings Journal

Why are mussels, barnacles and oysters able to stick themselves at objects like rocks, to a pier or to a vessel? And - most important - what we can learn about it and how can the coatings industry make use of this knowledge?

Observing nature

Mussels, barnacles and oysters are able to attach to wet objects in marine environment. If we try to glue something with commercially available adhesives in the presence of water – we normally fail. Water is not a warmly welcomed companion, if you consider adhesion processes. An important question is: How are mussels and similar organisms solving the problem of water being present during adhesion processes and what can we do with these findings?

Explaining nature

DOPA units (3,4-dihdroxyphenylalanine, catechol moieties) embedded in proteins are responsible for this finding, which has already inspired researchers for developing new adhesives. Amazingly these biomimetic adhesives can even bond stronger than superglue. On the molecular level, catechol moieties are either able to build strong hydrogen bonds or they can build chelate complexes by coordinating metal ions – even under wet conditions.

Inspired by nature

For biomedical, and environmental applications in wet, and moist conditions, polymers with self-healing abilities are badly needed. Fortunately the researchers Herbert Waite, Jacob Israelachvili, and their coworkers report in the current issue of Nature Materials about self-healing of polymers in water. The special thing about it is, that they were able to realize this idea without incorporating metal ions – a crucial prerequisite for this principle being used in biomedical applications.

Testing the idea

The researchers were using polyacrylate, and polymethacrylate materials. The surface was modified by catechols, in which the hydroxy groups were protected with acid labile silyl groups. If the polymer was cut into two pieces and treated with an acidic aqueous solution of pH 3, the pieces rejoined and gave the same tensile strength as the uncut sample before. Due to the acidic medium the catechol units were deprotected and the ability to generate the sticky network of hydrogen bonds is therefore reconstituted.

Remaining questions and having a look into the future

Nevertheless there are remaining questions which need to be answered. For example: How can one generate such an acidic environment, obviously necessary to reconstitute the free hydroxy groups? Can this perhaps be realised by microcapsules filled with acidic compounds? Are there different protecting groups which can be split of in different pH ranges? Are the byproducts of the deprotection reaction harmful for the quality of the coating on the long run?
I am really curious, if this principle will find its way into the coatings world, as it would be a great asset especially for moist work environments hard to reach and for settings, where it is necessary to avoid potentially harmful components like metal-ions.

Now it’s your turn!

What is your opinion? Do you have any suggestions or ideas?
I am looking forward to your comments and an interesting discussion!

Kind regards
Michael Richter

B. Kolbe, D. W. Lee, J. N. Israelachvili, J. H. Waite, Nature Materials 2014, 13, 867-872. Published online 27 Jul 2014. Read the article

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