15 April 2009

Bivalves have threads of steel

Many bivalves secrete byssus threads. These strong protein fibres cement the shell to hard surfaces and supports.
Pen shell (Pinna sp.)
Burying bivalves, like the Fan shell (Pinna sp.) above, may use byssus threads to literally root themselves to the surrounding sand or to small stones. The threads are produced by a gland near the foot.

Scientists have recently discovered how these threads can be both tough and elastic. They found that the tendon-like fibers in byssal threads are coated with a material that is both hard and extensible, and that iron and calcium are important ingredients in this material.

Further insights could lead to the development of futuristic coatings with optimal strength and flexibility for medical and industrial applications.

It's The Metal In The Mussel That Gives Mussels Their Muscle Power
ScienceDaily 13 Apr 09;
Researchers in California are reporting for the first time that metals are key ingredients that give the coatings of anchoring byssal threads of marine mussels their amazing durability.
Researchers report that metals are key to the amazing strength of mussel byssal threads, which firmly anchor the animal to wave-swept rocks. Shown is the damaged cuticle of a byssal thread. (Credit: The American Chemical Society)

The study could lead to the design of next-generation coatings for medical and industrial applications, including surgical coatings that protect underlying tissues from abrasion and also life-threatening bacterial infections, the researchers say.

In the new study, Herbert Waite and colleagues point out that many existing coatings are severely limited by the materials they cover. A rubber band dipped in molten wax is a good case in point. Once hardened at room temperature, the wax is several times harder and stiffer than the underlying rubber, but even moderate extension shatters the wax. Scientists have been trying for years to develop robust coatings for soft or delicate underlying materials.

Until recently, however, scientists knew little about the chemical mechanisms that allow mussels to coat the tendon-like fibers in byssal threads with a material that is both hard and extensible.

The researchers conducted a detailed chemical analysis of the protective outer coating of the byssus in a common species of marine mussel. They found that removing iron and calcium from the coating resulted in a 50 percent decrease in hardness, demonstrating that these metals play a key role in maintaining its integrity. Further insights could lead to the development of futuristic coatings with optimal strength and flexibility for medical and industrial applications, they note.

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