Why are Seashells So Strong? Researchers Uncover the Micelles Mystery

Researchers at the US Department of Energy’s Pacific Northwest National Laboratory have just discovered what gives sea shells their amazing strength: micelles. And with this breakthrough they’re paving the way for advances in renewable energy technologies.

It began with a straightforward enough question – how do seashells and lobster claws get to be so strong when they’re mostly made out of calcium carbonate, i.e. chalk? Mechanics has been the answer so far. Calcium carbonate crystals were said to form when particles (organic elements and proteins, for instance) land on the crystallizing surface and get locked into the physical shape of the crystal.

The problem with this theory was that it didn’t explain how biominerals such as seashells and exoskeletons develop their compressive strain – the force within the structure that gives it its integrity and strength.

This is where the DOE’s research team used atomic force microscopy to create three-dimensional images of the calcium carbonate crystals in order to figure out just how the crystallization process takes place. The team used a type of calcium carbonate known as calcite, as well as a group of organic particles called micelles, to initiate the crystallization process.

It turns out that crystallization creates uneven, step-like grooves on the substrate surface which attract the micelle particles due to the chemical makeup of the step edges. This creates a chemical bond between particle and calcite that keeps the particle in place while the crystallizing continues around it, building up layer upon layer until the micelle particle is buried and effectively squeezed in place – hence the compressive strain within the crystal.

“The steps capture the micelles for a chemical reason, not a mechanical one, and the resulting compression of the micelles by the steps then leads to forces that explain where the strength comes from,” says materials scientist Jim De Yoreo.

Figuring out how biominerals like seashells work is key to building synthetic materials with similarly advantageous qualities. De Yoreo says, “This work helps us provides us with ideas for trapping carbon dioxide in useful materials to deal with the excess greenhouse gases we’re putting in the atmosphere, or for incorporating light-responsive nanoparticles into highly ordered crystalline matrices for solar energy applications.”

Canada is already a leading player in carbon capture and storage (CCS) technology, with projects up and running in Saskatchewan (the Boundary Dam Project) and Alberta (the Alberta Carbon Trunk Line and the Quest project).

There is recent news in support of renewable technology, as well. November of this past year saw Ontario’s provincial government release its climate strategy, including a plan to reduce greenhouse gases to 80% below 1990 levels by 2050 and a cap and trade system that aims to encourage innovation in clean technologies.

Federally, following up on the Paris climate talks the Liberal government plans to reach an agreement with the provinces by March of this year on a national climate strategy. And further afield, the Canadian government will soon be in talks with the United States and Mexico on a North American climate strategy.

The DOE study was published in the journal Nature Communications and was supported by the US Department of Energy Office of Science, National Institutes of Health.

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