This Tiny Robot Mimics the Mantis Shrimp's Mighty Punch

Mantis shrimp has one of nature's most powerful punches. It is comparable to a.22 caliber bullet. Scientists are eager to study the biomechanics of the mantis shrimp, making it an appealing object for research. It could also be used to create small robots that can perform equally fast and powerful movements. A Harvard University team has now created a biomechanical model of the mantis shrimp's powerful appendage. It then built a tiny robot that mimics the movement. According to a paper published in the Proceedings of the National Academy of Sciences.
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Robert Wood, a senior author at Harvard University's John A. Paulson School of Engineering and Applied Sciences, stated that we are amazed by the amazing behaviors found in nature. Complex underlying mechanisms are responsible for the speed and force of mantis-shrimp strikes. We can study these mechanisms in unprecedented detail by creating a robotic model for the mantis shrimp striking appendage.

Wood's research group was a major player in the creation of RoboBee, which is a small robot that can fly partially untethered. This initiative aims to create a network of small, interconnected robots capable sustaining untethered flight. It is a challenging technological challenge due to the size of the insects, which alters the forces at work. Wood's team announced in 2019 that it had created the RoboBee X-Wing, an improved version of its insect-scale robot. It was described by Kenny Breuer in Nature as "a tour de force in system design and engineering."

Wood's group now focuses on the biomechanics behind the mantis shrimp's incredible punch. We've already reported that mantis shrimp can come in many forms. There are 450 species. They can be divided into two groups: those that stab prey with spear-like appendages ("spearers") or those that smash prey with large, round, and hammerlike claws ("raptorial appsendages") These strikes can be so powerful (up to 23 meters per second or 51 mph), and they produce cavitation bubbles within the water. This creates a shock wave that can be used as a follow up strike. It can sometimes kill the prey. Sonoluminescence can be produced when cavitation bubbles collapse, causing a flash of light to briefly illuminate the prey.

A 2018 study found that the secret to the shrimp's powerful punch is not bulky muscles, but the spring-loaded anatomical structure in the shrimp's arms. It's similar to a bow & arrow or mousetrap. The shrimp's muscles pull against a saddle-shaped structure within the arm. This causes it to bend and store energy. It is then released by the swinging club-like claw. It is essentially a latch-like mechanism, technically called Latch-mediated Spring Actiation (or LaMSA). The latch is held in place by small structures within the muscle tendons known as sclerites.

This is all well known and many other small organisms can produce ultra-fast movements through a similar latching mechanism. For example, chameleons' tongues and frogs legs, as well the mandibles and trap jaw ants' mandibles. Biologists have observed something unique in the mantis shrimp's latching mechanism. There is a 1 millisecond delay between the unlatching action and the snapping action.

The striking process can be seen on an ultra-high speed camera. There is a delay between the time the sclerites release, and when the appendage fires. This was observed by Nak-seung Hyun, co-first author, who is also a postdoctoral fellow in SEAS. It's like a mouse triggers a mousetrap, but instead of the trap snapping immediately, there is a noticeable delay until it snaps. The appendage is held in place by another mechanism, but it's not clear how that mechanism works.