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Mantis shrimp are renowned for their incredible striking ability, capable of delivering a blow with the force equivalent to that of a .22 caliber bullet, yet they remain unscathed after their own powerful punches. Recent research from Northwestern University has unveiled the mechanisms that allow these remarkable creatures to withstand the shockwaves produced by their strikes.
The research details how the dactyl clubs—striking appendages of mantis shrimp—are designed with layered patterns that effectively filter out harmful sound vibrations generated during their punches. This innovative structure serves as a protective shield against the intense shockwaves created with each impact. The findings are set to be published in the journal Science on February 7.
These insights may pave the way for advancements in synthetic materials aimed at enhancing protective gear, potentially providing solutions to diminish blast-related injuries within military applications as well as in various sporting contexts.
“The mantis shrimp’s powerful strike is capable of breaking through hard mollusk shells and even cracking aquarium glass,” explained Horacio D. Espinosa, co-corresponding author of the study at Northwestern. “For the mantis shrimp to repeat these high-impact strikes and avoid injury, its dactyl club must be equipped with a robust protective system. Prior research primarily concentrated on the toughness of the club, addressing it as merely a hardened shield against impacts. Our discovery highlights the role of phononic mechanisms—structures that selectively filter stress waves—allowing mantis shrimp to maintain their formidable striking capabilities while minimizing damage to their soft tissues.”
Espinosa is distinguished in the field of bio-inspired materials and serves as the James N. and Nancy J. Farley Professor in Manufacturing and Entrepreneurship at Northwestern’s McCormick School of Engineering. He collaborates closely with M. Abi Ghanem from the Institute of Light and Matter, a research unit that combines expertise from Claude-Bernard-Lyon-I University and the French National Center for Scientific Research.
A Striking Mechanism
Mantis shrimp inhabit shallow tropical waters and possess a dactyl club on each side of their bodies, which is essential for both offense and defense. These clubs harness energy through elastic, spring-like structures, locked in place by latch-like tendons. Once released, this stored energy propels the club with explosive force, making it a formidable weapon.
With each strike, mantis shrimp are capable of incapacitating prey or defending their territory against rivals. As their clubs penetrate the water, they generate a low-pressure zone that leads to bubble formation.
Espinosa elaborated, “The impact from a mantis shrimp’s strike produces pressure waves on the target and creates bubbles that rapidly collapse, resulting in high-energy shockwaves in the megahertz range. These collapsing bubbles release sharp bursts of energy that travel through the shrimp’s club, compounding the effects of both the initial strike and the secondary shockwave, thereby amplifying the club’s destructive power.”
Guarding Against the Force
Despite the remarkable force of their strikes, mantis shrimp manage to protect their vulnerable nerves and tissues, which are shielded by their armored structure. The researchers employed cutting-edge technologies, including transient grating spectroscopy and picosecond laser ultrasonics, to explore the intricate design of the mantis shrimp’s armor in detail.
The analysis revealed two specialized regions within the shrimp’s club. The first is the impact region, composed of mineralized fibers arranged in a herringbone pattern that enhances resistance to fractures. Below this lies a periodic region characterized by twisted, corkscrew-like fiber bundles forming a Bouligand structure. This complex arrangement allows each layer to be rotated relative to its neighbors.
While the herringbone structure bolsters the club’s overall strength, the twisted fibers manage the propagation of stress waves. This sophisticated design functions as a phononic shield, effectively filtering out high-frequency stress waves that could otherwise cause harm.
Espinosa noted, “The periodic region is vital in filtering out high-frequency shear waves, which are particularly harmful to biological tissues. This filtering process protects the mantis shrimp from the damaging stress waves produced by direct impacts and bubble collapses.”
The researchers conducted 2D simulations to study wave behavior, highlighting the necessity for subsequent 3D simulations to thoroughly examine the complex structure of the dactyl club. Espinosa expressed the need for further exploration, stating, “Future studies should focus on comprehensive 3D simulations to grasp how the club’s unique structure interacts with shockwaves. Additionally, experiments conducted in aquatic environments using state-of-the-art instrumentation could uncover how phononic properties operate when submerged.”
The study, titled “Does the mantis shrimp pack a phononic shield?” received support from the Air Force Office of Scientific Research, the Office of Naval Research, and the National Science Foundation.
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