Scientists are perpetually seeking methods to enhance the toughness, safety, and durability of inherently brittle building materials like concrete and ceramic. Their latest inspiration comes from an unexpected source: the incredibly strong shells of oysters.

Nacre, also known as mother-of-pearl, is the iridescent composite material that lines the inner layer of an oyster's shell. This widely recognized material from the jewelry industry is also an architectural marvel. It consists of microscopic hexagonal aragonite tablets (a common form of calcium carbonate) bound together by a soft biopolymer, similar to an organic glue.

The aragonite tablets contribute to nacre's strength, while the biopolymer offers flexibility. This synergy between hard and soft components is crucial to nacre's remarkable mechanical properties, according to Shashank Gupta, a co-author of the study and graduate student at Princeton University's Department of Civil and Environmental Engineering. He stated in a press release, "If we can engineer concrete to resist crack propagation, we can make it tougher, safer and more durable."

Inspired by nacre's structure, Gupta's team at Princeton investigated whether this biological adaptation, honed by over half a billion years of evolution, could be leveraged to improve human building materials. Their findings were published earlier this month in Advanced Functional Materials.

To test this concept, the researchers created three distinct types of multi-layered material beams. Each beam alternated between cement paste sheets and a thin polymer layer. The first beam simply stacked these two elements, while the other two incorporated variations. One featured hexagonal grooves etched into the cement paste, and the other included complete hexagonal cutouts, forming nacre-like tablets. These three designs were compared to a standard cast cement paste beam (without polymer layers or hexagonal features).

The experiments demonstrated that all three beams exhibited significantly increased ductility and toughness compared to the brittle reference beam with no ductility. However, the most impressive results came from the multi-layered beam featuring the nacre-inspired hexagonal plates. By mimicking the mechanics of microscopic nacre, this beam achieved 17 times greater toughness and 19 times more ductility than the standard cast cement, all while maintaining a strength comparable to the reference beam.

"Our bio-inspired approach is not to simply mimic nature's microstructure but to learn from the underlying principles and use that to inform the engineering of human-made materials," explained Reza Moini, a co-author of the study, in a press release. "One of the key mechanisms that makes a nacreous shell tough is the sliding of the tablet at the nanometer level. In other words, we intentionally engineer defects in the brittle materials as a way to make them stronger by design."

The development of stronger and safer cement would not only benefit the construction industry but also contribute to environmental well-being, as cement production is responsible for roughly 8% of global greenhouse gas emissions. While this study presents promising results for nacre-inspired materials, the multi-layered, hexagonal-plated technique requires further refinement before widespread adoption in construction.