April 25, 2026

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Mollusk shells could pave the way to greener materials

Nacre-inspired ceramics could be the basis for the next generation of energy-efficient technology

By Caitlin Kennedy edited by Clara Moskowitz

Melanie Jones/Getty Images

In 59 B.C.E. Julius Caesar, future dictator of Rome, gifted his favorite mistress Servilia a black pearl earring of such size and luster that it was chronicled by many Roman writers of the day.

Caesar reportedly paid six million sesterces (hundreds of millions of dollars today) for the gem, making it one of the most extravagant displays of affection the world has ever seen. Although the cost was exceptional, his gift of a pearl was not. After all, pearls were a cornerstone of ancient Rome’s political and economic power.

Cheaper imitations and modern methods of culturing have considerably diminished the value of natural pearls since then. But nacre, the lustrous substance mollusks use to line their shell, is becoming prized once more, this time in materials science.

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Nacre’s internal nanoscale architecture holds huge promise for researchers as they rush to create nature-inspired materials for a transition to clean energy without cost to Earth.

Natural Ceramic

Nacre is a natural ceramic; its inorganic building blocks arrange themselves in a neat geometric shape. Synthetic ceramics have become the bedrock of modern life, and they are now found in everything from hip replacements to cell phone casings. Not merely strong, so-called advanced ceramics are inert and able to withstand wear, corrosion and high temperatures, making them extremely useful. But as anyone who’s dropped a mug knows, ceramics are also brittle and prone to smashing.

Pearls, on the other hand, are made by soft-bodied mollusks in reaction to an irritant that has entered their shell. As part of an immune response, the mollusk secretes mother of pearl (nacre) and coats the particle until it becomes smooth and relatively round. It’s easy to understand why the Romans were enthralled; the substance seems to capture light and disperse it in a muted glow of iridescence, an effect caused by crystalline layers that are roughly the same size as the wavelength of visible light. Incoming light waves refract and interfere with one another as they bounce off the internal structure. But it isn’t their beauty that captivates materials scientists.

“When we started to look at the microstructure of these natural materials, like bone and nacre, we find they are very, very tough,” says Eduardo Gutierrez, director of the Center for Advanced Structural Ceramics at Imperial College London. In Gutierrez’s field, strength and toughness mean very different things. Toughness is about how much energy a material can absorb by deforming plastically, while strength measures how much force a material can resist before it gives way.

Pure ceramics are strong but brittle. Nacre is both strong and tough. “Although nacre’s cells are essentially 99 percent ceramic by volume, it is resistant to crack propagation. And it has a very interesting microstructure,” Gutierrez says.

Specifically, nacre is composed of hexagonal crystals of aragonite, a kind of calcium carbonate that is also seen in limestone and that forms precisely into overlapping layers that resemble the brick-and-mortar structure of buildings. The layers overlap out of alignment so that the joints between individual crystals, or “bricks,” don’t line up, increasing the number of hydrogen bonds in the overall structure and conferring it with strength. But where limestone is crumbly and opaque, nacre’s toughness and light-bending properties come from silklike proteins that weave among the layers, holding them in place while providing enough elasticity to absorb the shock of a fracture. In fact, nacre is roughly 3,000 times tougher than its calcium carbonate building blocks.

Until recently the way these different elements interacted at the nanoscale during crack formation was a mystery. But electron microscopy and other novel tools have vastly expanded our understanding of the composition of nacre, revealing the layers of calcium carbonate to be exceptionally thin, with individual crystal “bricks” interlocking in a dovetail shape that increases friction in the system and resists horizontal forces. Even more impressively, when you stretch those silklike polymers, Gutierrez says, “they have a particular behavior: they become stiffer.”

Synthetic Nacre

But even with ever more detailed electron microscopy, nacre has proved very difficult to manufacture