NIST develops impact-resistant material inspired by mantis shrimp exoskeleton

Certain creatures have unique microstructures in their exoskeletons that enable them to withstand heavy impacts continuously over time. These Bouligand structures can be found in the mantis shrimp, blue crab, glorious beetle and many more (shown here). Source |Shutterstock, B. Hayes/NIST

Researchers at the National Institute of Standards and Technology (NIST, Gaithersburg, Md., U.S.) have recently developed synthetic versions of the strong exoskeletons observed in mantis shrimp. When testing these bio-inspired structure’s impact performance by blasting them with microprojectiles, researchers discovered that adjusting specific parameters of the structures changed how they absorbed and dissipated the impact energy.

“The results and insights of this research mark an important advance in bio-inspired materials design with applications for aerospace, such as helping spacecraft survive the impact of micrometeoroids and protecting orbiting satellites that collide with debris,” explains NIST materials research engineer Edwin Chan. Other potential applications include better bullet-resistant glass, blast-resistant building materials and more protective helmets. Chan and his colleagues published their findings in the Proceedings of the National Academy of Sciences.

CW readers may be familiar with biomimicry through past articles that discuss how the interdisciplinary methodology could lend itself to the creation of more sustainable and effective composite materials, structural fabrication and technological practices (see part 1 and part 2). The mantis shrimp — capable of cracking clamshells with the force of a 0.22 caliber bullet, and the source of inspiration for NIST’s work — has also informed Helicoid Industries’ patented helicoid composite technology.

This research idea came from Sujin Lee, who came to NIST as a National Research Council (NRC) postdoctoral fellow. Lee wanted to understand why the mantis shrimp’s appendage didn’t break as it smashed the shells of other creatures. Chan was also intrigued by this concept, and the two developed a research project to find out.

The organism’s strong exoskeleton is related to microscopic Bouligand structures, a universal material platform for impact resistance in nature. Lee and Chan synthesized the structures from cellulose nanocrystals, which are found in plant fibers. The nanocrystals self-assembled into plates, which layered on top of each other like rotating stacks of plywood. Those stacks formed their synthetic Bouligand structures. Researchers then modified the crystals using high-frequency sound waves before assembling them into thin films that served as their test material.

Next, they tested the impact resistance of the thin films by firing microprojectiles at them at speeds of up to 600 meters/second. The microprojectiles, made of silica, were propelled toward their target by a high-intensity laser. The researchers recorded images of the microprojectiles impacting the thin films with an ultra-fast camera.

based on those images, NIST researchers observed that a microprojectile can leave a permanent indentation while also bouncing back like a tennis ball hitting the ground. The degree of indentation and the amount of bounce-back depended on how the energy dissipated or spread out in shockwaves after the microprojectile’s impact.

They also discovered that they could adjust how the energy dissipated by fine-tuning various factors that affected the sample’s mechanical properties, such as making the nanocrystals thicker or changing their density. The microprojectiles left permanent indentations in the thinner films, but the thicker films excelled at redirecting the shockwaves from the impact.

NIST worked on this project as part of its mission to develop advanced measurement methods that can be useful to U.S. industry. Researchers can use the measurement methods developed for this project to further develop impact-resistant materials based on Bouligand structures as well as other types of advanced materials with special properties.

“These findings suggest that there are different ways to design materials to absorb impact, and we can use this knowledge to create more resilient and longer-lasting materials,” Chan says. “If you’re a boxer in the ring, you want to fight nine rounds, not just one.”