Making unstickable adhesives: Mussel power

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  • Published: May 1, 2012
  • Author: David Bradley
  • Channels: UV/Vis Spectroscopy
thumbnail image: Making unstickable adhesives: Mussel power

A sticky problem

UV and NMR spectroscopy have been used to characterise a novel adhesive that functions in marine environments by mimicking the notoriously strong, natural glue used by mussels to cling to rocks and ships' hulls.

The bivalve molluscs known generically as mussels, have a well-known talent of sticking, through their byssal threads, or beard, to rocks, jetties and the underside of ocean-going vessels. Generations of sailors and those wishing to harvest edible mussels have been all too aware of its strengths.

Materials scientists and chemists have endeavoured (for not quite as many generations) to understand the chemistry that gives rise to this strength. One motivation is to find a way to reverse the bonding to make safer and more environment friendly anti-fouling agents for boats and underwater constructions. The second motivation is to take inspiration from this natural adhesive to create glues that are strong and also work in the marine environment for a wide ranging of oceanic engineering and other applications. A mussel-based adhesive for bathroom soap dishes could usefully replace the weak rubber suction systems that endlessly fail to maintain their grip on wet glazed ceramic tiles in bathrooms across the globe.

Now, a team in Mainz have muscled in on the marine adhesive arena and developed a biocompatible, waterproof and self-healing adhesive with one additional useful property - the glue can be "debonded" on demand. Such a reversible adhesive might have a wide range of engineering applications but could also be a boon to medicine particularly in surgery.

Tissue engineering

The researchers add that surfaces coated with this adhesive would also provide an appropriate substrate on which cells could grow and so a removable hydrogel pad made with the adhesive could be used in skin regeneration or tissue engineering.

A waterproof glue could fix leaks in underwater installations and pipelines, but a reversible waterproof glue could be used to staunch open wounds or stick damaged tissues and prosthetics together in the operating theatre. It could be used as a surgical superglue to avoid the need for sutures where a patient requires multiple operations on the same site, for instance. In addition, a glue that can be debonded and leave no residue would improve the recycling process for dismantling composite goods.

Spectroscopynow recently reported on work by Matthew Harrington, Admir Masic, and Peter Fratzl of the Department of Biomaterials, at the Max Planck Institute for Colloids and Interfaces, Potsdam, Germany, Niels Holten-Andersen at the University of California, Santa Barbara and the University of Chicago, and Herbert Waite also at UCSB who prised open the secret of the marine mussel's byssus using Raman spectroscopy. They probed the chemical composition of the cuticle of the mussel and obtained the first direct evidence that the cuticle has a protein-based polymeric scaffold stabilized by complexes of DOPA-iron the work helped explain how mussels keep their grip on rocky shorelines even in the stormiest tides.

The amino acid dihydroxyphenylalanine (DOPA) is critical to the mussel's grip. The DOPA groups react in a stepwise manner in seawater to form a cross-linked polymer matrix capable of bonding to inorganic oxides in rock. Mussel adhesive also has self-healing properties as it can bind to polyvalent metal ions, such as iron ions, in the seawater.

The researchers working with Aránzazu del Campo at the Max Planck Institute for Polymer Research in Mainz have produced four-armed, star-shaped polymers with nitrodopamine groups attached to their ends. These groups are chemical similar to DOPA and so help the adhesive to cross-link under water and endow it with similar self- self-healing properties to the original mussel adhesive. The team explains that if damaged the bond will reform within minutes if a gel sample is cut. Crucially, the nitro groups give this new adhesive the potential to be easily debonded. Irradiation with ultraviolet light will split the bonds quite readily.

Related Links

Angew Chem Int Edn, 2012, online: "Bioinspired Underwater Bonding and Debonding on Demand"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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