23 August 2005: Mussels flex their byssi

Mussels alter their binding behaviour in response to the properties of the surface to which they are binding, report British and American researchers.

Mussels bind to numerous different surfaces - from rocks to hulls of ships - by sending out multiple collagenous threads, called byssi, which firmly anchor the animals. Understanding more about this binding ability will help to develop environmentally-friendly anti-fouling coatings for the maritime industry and could lead to novel adhesives that work under water.

Researchers at the universities of Newcastle upon Tyne and Birmingham, UK, and the University of New Mexico, US, studied how well mussels bind to surfaces that differ solely in terms of wettability (the degree to which water spreads across a surface). To produce these surfaces, the researchers took microscope slides coated with chromium or gold and added a layer of CH₃-terminated or OH-terminated alkanethiolates, with the precise ratio between the alkanethiolates determining the surface’s level of wettability.

The researchers used these surfaces to study the number and size of byssi that were extended by immobilised mussels towards five different surfaces. In a separate study, the team allowed mussels to attach themselves to one of two different surfaces.

They discovered that mussels prefer to bind to surfaces with high levels of wettability, producing larger byssi on these surfaces, but that the animals produced more byssi threads when binding to surfaces with lower levels of wettability. 

One explanation for this finding, which is supported by previous research, is that the byssi form stronger adhesive bonds on surfaces with high levels of wettability. Mussels therefore extend more byssi to account for a loss in adhesion when binding to surfaces with low levels of wettability.

The researchers are now investigating other aspects of mussel attachment, as well as studying other adhesive-generating marine organisms. ’A similar study has been carried out for barnacle cypris larvae [an early developmental stage of barnacles, when they first attach to a surface],’ said researcher Nicholas Aldred from the University of Newcastle upon Tyne. 

’We are currently shifting our focus to the responses of these organisms (and their adhesives) to surfaces with similar water contact angles (a measure of free energy) but different charges,’ Aldred told Chemistry World. Jon Evans