Mar 5 2010
A research team studying the protective coatings on the byssal threads or 'beards' of mussels - the fibres by which mussels attach themselves to rocks - has found that they owe their strength and flexibility to their F protein and metal ion make-up. The findings, published in the journal Science, could prove highly useful for the future production of industrial materials.
The threads which are usually removed before mussels are cooked, are covered with an outer coating of protein and then with metal ions which make them extremely hard-wearing - vital for mussels in their watery habitat, where they have to anchor themselves firmly to rocks while being battered by waves and other sea materials.
In spite of their delicate appearance, molluscs are tough creatures that nature has designed to deal with the rigours of ocean life. The team of German and American researchers used the technique of Raman microscopy, in which particles as small as one micrometre can be identified, to study the byssal threads and identify their composition.
The outer cuticle of the byssal threads is composed of an amino acid called tyrosine, commonly known as dopa, which is a strong adhesive. The cuticle is also covered with iron ions. The result is a thread that is extremely hard, but can withstand cracking even under extreme conditions.
Dr Admir Masic from the Max Planck Institute said, 'When two to three dopa residues complex with a single iron ion, they create an incredibly stable complex that can be utilised to cross-link structural proteins.'
The byssal threads are an extraordinary feat of engineering, being at the same time hard, elastic, strong and flexible. They also have a 'knobbly' appearance which is due to submicron-sized granular structures that form an apparently continuous matrix. The team speculates that the tiny tears that form in the matrix when the thread stretches stop the matrix from tearing on a larger scale - a process that could be invaluable for making industrial materials stronger, more flexible and longer lasting.
'Protective coatings are important for prolonging the lifetime of materials and devices,' said researcher Dr Matthew Harrington from the Max Planck Institute. 'However, considering that hardness and extensibility are seldom coupled in engineered polymers or composites, understanding how one protects a flexible substrate becomes quite important.'
Dr Peter Fratzl, director of the biomaterials department at the Max Planck Institute, said, 'Nature has evolved an elegant solution to a problem that engineers are still struggling with, namely, how to combine the properties of abrasion resistance and high extensibility in the same material. Apparently, the cuticle achieves this through a careful tailoring of protein-metal chemistry and the submicron organisation of cross-link density. Conceivably, this same strategy could be applied in engineered polymers and composites.'
Source: Cordis