"In this work, we were specifically trying to understand how the threads are fabricated and how the metals were incorporated. The insights will have implications for bio-inspired polymers and adhesives.”Matthew Harrington
An international research team led by scientists at McGill University in Canada have uncovered the cellular mechanism by which mussels produce the strong underwater glue that keeps them tethered even in strong waves and churningcurrents. Their breakthrough could help inspire more sustainable ways of producing polymer materials and plastics, as well as the next generation of high-performance adhesives and plastics used in wet environments such as in surgical or dental treatments.
Mussels can remain attached to rocks or other mussels due to the very effective underwater glue they produce. Until now, the mechanism by which mussels produce their adhesive has remained unknown as everything occurs inside an organ known as the mussel foot and is hidden from view. To investigate the mechanisms involved, advanced spectroscopic and microscopic techniques were used in an experimental approach combining methodologies from across biochemistry, chemistry and materials science.
The researchers have studied the byssal threads of blue mussels (Mytilus edulis) for nearly 20 years as they combine high toughness, self-healing capacity and the ability to adhere to almost any surface chemistry under seawater conditions, something that even engineering glues cannot achieve. At the end of each thread is a disc-shaped plaque that acts as an underwater glue.
As reported in Science [Priemel et al. Science (2021) DOI: 10.1126/science.abi9702], mussels were found to mechanically reinforce byssal threads from metal ion-rich vesicles secreted beside vesicles containing an adhesive protein, which then combine in a microfluidic-type process in microchannels located in the mussel foot to produce porous and adhesive plaque filaments. The proteins are in a condensed fluid phase, and are mixed in the channels with small metal rich particles that slowly release iron and vanadium ions that mix with proteins, which causes them to cross-link and harden.
As Matthew Harrington, senior author on the paper, told Materials Today, “We never understood where the metals came from or how they were added during thread formation. In this work, we were specifically trying to understand how the threads are fabricated and how the metals were incorporated. The insights will have implications for bio-inspired polymers and adhesives.”
The team are now looking at how the condensed fluid protein phases used by the mussels are physically and chemically processed to produce materials with complex multiscale structure and mechanics, as well as how the special chemistry of vanadium is controlled and harnessed by the mussel to produce materials with dynamic mechanical properties. The use of vanadium is of particular interest as there are not many organisms that are known to hyperaccumulate vanadium.
Mussels mechanically reinforce their byssal threads from metal ion-rich vesicles