The mantis shrimp has one of nature’s most powerful and fastest punches, with a force comparable to that of a.22-caliber bullet. This makes the species an appealing research subject for academics interested in learning more about pertinent biomechanics. It could lead to miniature robots capable of equally fast and forceful movements, among other things.
According to a recent publication published in the Proceedings of the National Academy of Sciences, a team of Harvard University researchers developed a new biomechanical model for the mantis shrimp’s formidable appendage and created a tiny robot to emulate that movement.
“We are fascinated by so many remarkable behaviors we see in nature, in particular when these behaviors meet or exceed what can be achieved by human-made devices,” explained senior author Robert Wood, a roboticist at Harvard University’s John A. Paulson School of Engineering and Applied Sciences (SEAS). “The speed and force of mantis shrimp strikes, for example, are a consequence of a complex underlying mechanism. By constructing a robotic model of a mantis shrimp striking appendage, we are able to study these mechanisms in unprecedented detail.”
RoboBee, a tiny robot capable of partially untethered flight, was built by Wood’s research group few years ago, and it made headlines. The initiative’s ultimate goal is to create a swarm of tiny networked robots capable of continuous untethered flight—a considerable technological challenge given the insect-size scale, which alters the numerous forces at play.
Based on a 2018 study, the secret to the shrimp’s tremendous punch appears to be the spring-loaded anatomical structure of its arms, similar to a bow and arrow or a mousetrap. Muscles in the shrimp’s arm pull on a saddle-shaped structure, allowing it to bend and store potential energy, which is released when the club-like claw swings. It’s essentially a latch-like mechanism (officially known as Latch-mediated spring actuation, or LaMSA), with the latch being little structures called sclerites found in the muscle tendons.
In 2019, Wood’s team announced the development of the RoboBee X-Wing, the lightest insect-scale robot to have achieved sustained, untethered flight to date. (It was called “a tour de force of system design and engineering” by Kenny Breuer in Nature.)
Wood’s team is now focusing on the biomechanics of the mantis shrimp’s knock-out punch. Mantis shrimp occur in a wide variety of species, as we’ve already mentioned; there are over 450 identified species. However, they can be divided into two groups: those who stab their victims with spear-like appendages (“spearers”), and those who smash their prey with massive, rounded, and hammer-like claws (“smashers”) (“raptorial appendages”).
They utilized the same unique manufacturing technology inspired by pop-up books (pop-up book MEMS) that Wood’s group used to produce RoboBee for their robot version of the mantis shrimp appendage. Cutting designs from flat sheets, layering them, gluing the layers together, and folding them into the necessary shapes are all part of the process. Piezoelectric actuators can be used to create a miniature version of “artificial muscle,” while small plastic hinges are ideal for rotating motion. Then they ran a series of tests in both air and water under two different loading scenarios.
They were able to distinguish four distinct striking phases and confirm that the rapid acceleration after the initial unlatching by the sclerites is caused by the geometry of the mechanism. The performance of the little robot mechanism wasn’t quite on par with that of a mantis shrimp, but it did reach 26 meters per second in the air, which is the equivalent of a car going from 0 to 58 mph in just 4 milliseconds. While not quite as quick as the real thing, it’s still impressive.
A study published last year discovered that the mantis shrimp punches at half the speed in air, implying that the mantis shrimp can precisely control its striking behavior depending on the medium. According to Hyun, their water-based experiments revealed a “added mass effect.” “In fluid mechanics, when you move really quickly, you’re actually pushing a heavier mass,” he explained. This effect was minimal in the RoboBee experiments because it operates in air, but it is a critical variable when simulating the mantis shrimp strike in water.
The brief time between unlatching and snapping The authors wrote that “is likely a crucial feature enabling repeated and extreme use without the wear and tear of contact latching mechanisms,” They hope to apply their strategy of combining physical and analytical modeling to other species in the future, such as the underlying mechanisms of trap jaw ants or leaping frogs.
Since such hits are so quick (up to 23 meters per second, or 51 miles per hour) and forceful, they frequently cause cavitation bubbles in the water, causing a shock wave that can act as a follow-up strike, paralyze and sometimes kill the target. When a strike occurs, the cavitation bubbles produce a brief flash of light as they collapse, which is known as sonoluminescence.