Mantis shrimp, renowned for their astonishing punching power, can break shells with force comparable to a .22 caliber bullet. Remarkably, these resilient creatures endure intense shockwaves produced by their own strikes without sustaining any harm.
Researchers from Northwestern University have uncovered the secrets behind how mantis shrimp avoid injury from their powerful hits. Their striking appendages, known as dactyl clubs, showcase layered designs that filter sound selectively. These patterns block certain vibrations, functioning as a barrier against the shockwaves they create.
This research will be published on Friday (Feb. 7) in the journal Science.
Insights gained from this study could pave the way for innovative materials designed to reduce the risk of blast-related injuries, especially in military and sports applications.
“The mantis shrimp is famous for its incredibly forceful strike, capable of shattering mollusk shells and potentially breaking aquarium glass,” noted Horacio D. Espinosa from Northwestern, a co-corresponding author of the study. “For the mantis shrimp to perform these intense strikes repeatedly, its dactyl club needs a strong protective mechanism that prevents self-inflicted damage. Previous research primarily focused on enhancing the club’s toughness and ability to resist cracking, treating it like a rugged shield. Our findings highlight that it employs phononic structures that selectively filter stress waves, allowing the shrimp to maintain its striking power across multiple impacts while protecting its softer tissues.”
An expert in bio-inspired materials, Espinosa holds the James N. and Nancy J. Farley Professorship in Manufacturing and Entrepreneurship and teaches mechanical engineering at Northwestern’s McCormick School of Engineering. He also directs the Institute for Cellular Engineering Technologies, leading the study in collaboration with M. Abi Ghanem from the Institute of Light and Matter, a joint research group between Claude-Bernard-Lyon-I University and the Center for National Scientific Research in France.
The Impactful Strike
Nesting in shallow, tropical waters, mantis shrimp possess a hammer-like dactyl club on each side of their body. These clubs utilize elastic, spring-like structures to store energy, secured by latch-like tendons. Upon releasing the latch, the stored energy is unleashed, propelling the club forward with explosive force.
With one swift blow, mantis shrimp can capture prey or fend off rivals. As their punch cuts through the water, it creates a low-pressure zone that leads to bubble formation.
“When the mantis shrimp strikes, it produces pressure waves directed at its target,” Espinosa explained. “This also creates bubbles that collapse rapidly, generating shockwaves in the megahertz range. The collapse releases intense bursts of energy that travel through the shrimp’s club, enhancing the impact effect’s devastation alongside the initial force.”
Protective Design
Remarkably, this powerful force does not harm the shrimp’s delicate nerves and tissues, which are shielded by its armor.
To delve into this phenomenon, Espinosa and his team utilized two sophisticated techniques to closely analyze the mantis shrimp’s armor. First, they employed transient grating spectroscopy, a laser technique to evaluate how stress waves move through materials. Additionally, they used picosecond laser ultrasonics for deeper insights into the armor’s microstructure.
Their research identified two distinct regions within the mantis shrimp’s club, each engineered for specific functions. The impact region is designed for delivering crushing strikes and contains mineralized fibers arranged in a herringbone pattern, which enhances its breakage resistance. Below this layer lies the periodic region, featuring twisted, corkscrew-like fiber bundles. These form a Bouligand structure—a layered design in which each layer is gradually rotated in relation to its neighbors.
While the herringbone pattern strengthens the club against cracks, the corkscrew design manages the stress wave movement. This complex construction acts as a phononic shield, selectively filtering out high-frequency stress waves, which helps prevent damaging vibrations from affecting the shrimp’s arm and body.
“The periodic region is vital for filtering high-frequency shear waves that can be particularly harmful to biological tissues,” Espinosa remarked. “This mechanism shields the shrimp from negative stress waves caused by both direct impact and bubble collapse.”
In their study, researchers ran 2D simulations to examine wave behavior. Espinosa noted that comprehensive 3D simulations are necessary for a thorough understanding of the club’s intricate architecture.
“Future research needs to focus on more advanced 3D simulations to entirely capture how the club’s design interacts with shockwaves,” Espinosa stated. “Moreover, conducting aquatic experiments with cutting-edge instruments would help us explore how phononic properties perform in submerged environments.”
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.
