Materials scientists often turn to nature for inspiration and the well-known and powerful punch of the mantis shrimp could be the next target for a biomimetic material.

Researchers in Singapore can now explain what gives the mantis shrimp, Odontodactylus scyllarus, the power to club its prey to death with what is the most powerful punch in the animal kingdom. They show that a mineralized, saddle-shaped structure in the mantis shrimp's limbs, acts like a spring to store and then release energy. The composite of biomineral and biopolymer could offer insights into how to make powerful actuators for microelectromechanical systems (MEMS) or even robotic components. The team's simulations of this punching polymer reveal how it can store large amounts of elastic energy without breaking.

"Nature has evolved a very clever design in this saddle," explains Ali Miserez of Nanyang Technological University in Singapore. He adds that if it were made of a single homogeneous material it would be far too brittle to pack any kind of punch and would simply break when used.

Previous research from the lab of biologist Sheila Patek had examined the mantis shrimp's dactyl clubs - the appendages they use to attack their prey - and suggested that muscles alone couldn't be creating the amount of force with which the crustaceans strike. Other research had hinted at the elastic storage capacity of the saddle structure. Extracting the details is tough because the movement is so rapid. So, the team analyzed the composition of the saddle, making micro-measurements of its mechanical properties so that they could build a computer model and simulate the mantis shrimp strike. They showed that the top layer of the saddle is mainly a relatively brittle bone-like bioceramic, whereas the underside is mainly fibrous biopolymer and tough.

"If you asked a mechanical engineer to make a spring that can store a lot of elastic energy, they wouldn't think of using a ceramic. Ceramics can store energy if you can deform them, but they're so brittle that it wouldn't be intuitive," explains Miserez. "But if you compress them, they're quite strong. And they're stiffer than metal or any polymer, so you can actually store more energy than you could with those materials."

The team is already 3D printing components inspired by the mantis shrimp saddle, which they suggest might be used in microrobotics. [Tadayon, M. et al. iScience (2019); DOI: 10.1016/j.isci.2018.08.022]