Shrimp’s attack club distributes impact among spiraled layers of fibers
Introduction
It’s important that things don’t break, whether it’s things like airplanes, bridges, or coffee cups. What if it were your body itself on the line? For some creatures that’s the case, which is why material scientists look to creatures like the rainbow mantis shrimp for ideas about how to make materials stronger.
The peacock mantis shrimp, a multi-colored 5-inch crustacean that lives in coral reefs from Guam to East Africa, hunts shellfish by smashing through their hard shells using its club-shaped appendage. Its club travels faster than 50 mph (80 kph), exceeding the speed of a bullet from a .22 caliber gun, traveling so fast that the seawater literally boils in the club’s wake. Their formidable club makes members of this species dicey to keep in an aquarium, because they’ve been known to punch through the glass.
The mantis shrimp's club is highly resistant to impact thanks to helicoid layers of varied composite materials, including chitin.
The Strategy
The mantis shrimp’s club is made of intricately designed material to make it especially crack-resistant. A strong calcium-based mineral surrounds the outside of the club. Below this layer, the club’s design is dominated by the orientation of mineralized fibers.
The shrimp uses long chains of carbohydrates to attract, orient, and solidify inorganic minerals out of the surrounding seawater. The resulting fibers of calcium carbonate and calcium phosphate are biomineralized into circular layers, which resist sideways expansion during impact, keeping the club together.
Between these circular layers, sheets of blended (composite) materials made of chitin and are stacked one upon the other, each set of fibers rotated slightly from the fiber alignment below. This creates a spiraled structure in cross-section, like a twisted stack of printer paper. This spiraled region of the shrimp’s club helps absorb the impact from each blow, much like a spring, and channels any cracks that do form in the club around within the club’s material, weakening their force and preventing straight cracks from forming and splitting the club apart.
The 3D model at left illustrates the structure of the mantis shrimp’s dactyl club and telson as revealed by an electron scanning microscope image at right.
The Potential
New human-made materials using insights from the way the rainbow mantis shrimp’s club is designed are much tougher. By one measure, materials inspired by the shrimp’s club were up to 20% stronger than materials made of the same substance but without the shrimp club’s internal architecture. Human-made materials inspired by nature can be used to create stronger and safer things humans use and rely upon daily, such as bridges, buildings, and even the keyboard you’re tapping on.
