Sea urchin spines inspire fracture-resistant cement

"If we succeed in designing the structures of materials and reproduce nature's blueprints, we will also be able to produce much more fracture-resistant materials," researcher Helmut Cölfen said.
By Brooks Hays  |  Nov. 30, 2017 at 12:24 PM
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Nov. 30 (UPI) -- Inspired by the unique structure of sea urchin spines, scientists at the University of Konstanz have developed a new way to make cement more resistant to fracturing.

The shells of sea urchins are made of calcite, a relatively brittle material. But the small bumps, or spines, that adorn the shells are surprisingly strong. A brick wall-style architecture accounts for their sturdiness.

Researchers at Konstanz found a way to replicate the brick wall-style structure at the nanoscale, coaxing macro-molecules in cement to work like mortar, holding together precisely arranged crystalline blocks.

"Our cement, which is significantly more fracture-resistant than anything that has been developed thus far, provides us with completely new construction possibilities," Helmut Cölfen, a professor of physical chemistry at Konstanz, said in a news release.

Brick wall-style assembly on the nanoscale is similar to its macro scale reference point -- hard materials stacked atop soft materials, arranged to create a layered or patterned structure.

The crystalline blocks in the sea urchin's calcite shell don't crack because they transfer the energy of outside forces onto the surrounding layer of softer, disordered material -- the mortar. For sea urchins, the mortar is calcium carbonate.

Cement is mostly amorphous. It lacks the kind of patterned structure that lends the shells of sea urchins and mussels their surprising strength and durability. To enhance its resistance to fracture, Cölfen says he and his researchers worked to encode greater structural order at the nanoscale.

To do so, scientists first identified materials that bond exclusively with cement nanoparticles. Cölfen and his colleagues keyed in on ten negatively charged combinations of peptides. Scientists used the peptides as mortar to structure cement nanoparticles.

Using an electron microscope, scientists excised a bar-shaped micro-structure from their new cement. They used a micro-manipulator to bend the micro-structure and measure its elasticity. Their findings -- published this week in the journal Science Advances -- showed the cement was incredibly resistant to fracture. The micro-structure earned a value of 200 megapascals. A mussel shell's resilience measures 210 megapascals.

Scientists are now working on scaling up their process for synthesizing nanoscale-structured cement.

"People have much better construction materials than calcite," Cölfen said. "If we succeed in designing the structures of materials and reproduce nature's blueprints, we will also be able to produce much more fracture-resistant materials -- high-performance materials inspired by nature."

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