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Mussel filaments prove that harder isn't necessarily stronger

Researchers at MIT have found mussels adhere themselves to rocks in rough waters using a strategic combination of hard and soft material that could have applications in engineering.

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MIT scientists have found that mussels affix them themselves to surfaces using highly strategic filaments that are both hard and soft.

Zhao Qin

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Softer, better, faster, stronger?

Mussels affix themselves to surfaces using a bundle of thin filaments that are at once hard and soft, a strategic hybrid that could be a potential model for engineers, scientists have found.

The research joins increasing attention to natural models as solutions to problems in engineering. There, in spider webs and rice leaves and shark skin, is where scientists have found elegant and efficient answers to major design troubles. Often, nature recommends a compelling blend of firmness and softness – similar to that seen in the mussel filaments – that seems counterintuitive: harder does not always mean stronger.

Scientists had known that mussels, a button-sized, blue-black-shelled mollusk, use a kind of glue to adhere to various surfaces. That anchoring allows the animals to collect food from the Northeastern shores without getting knocked from their perches in the strong surf.

But researchers had also known that the glue was insufficient to explain how the mussel managed to weather the extreme force of pounding waves: Mussels, after all, can withstand multidirectional impact forces that add up to more more than nine times that of the forces exerted in any single direction.

“Although it the glue is strong, it is not strong enough to fight against crushing waves,” said Zhao Qin, a research scientists at MIT and a co-author on the study, published in Nature Communications. “So we started this study to look at the mussels’ threads.”

Mussels also use a collection of filaments, called byssus threads, to pin themselves to surfaces. But the byssus threads had also been a vexing part of the problem: how did that network of ultra-thin, fragile-looking filaments - no wider than human hair - support the tiny, clinging animal in the ocean’s roar?

In 2011, MIT researchers placed a cage of mussels and surfaces including glass, ceramics, and wood into the Boston Harbor for three weeks. After the mussels have affixed themselves to those surfaces, the cage was brought to the lab, where the mussels, the threads they had spread, and their surfaces of choice were mounted in a tensile machine that could test their strength, subjecting the fibers to controlled deformation and recording the applied force.

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