Bioinspired Soft Robotic Fish for Wireless Underwater Control of Gliding Locomotion

Abstract

Animal locomotion offers valuable references as it is a critical component of survival as animals adapting to a specific environment. Especially, underwater locomotion poses a challenge because water exerts a high antagonistic drag force against the direction of progress. However, marine vertebrates usually use much lower aerobic energy for locomotion than aerial or terrestrial vertebrates due to their unique intermittent gliding locomotion. None of the prior works demonstrate the locomotive strategies of marine vertebrates. Herein, an untethered soft robotic fish capable of reconstructing the marine vertebrates’ effective locomotion and traveling underwater by controlling localized buoyancy with thermoelectric pneumatic actuators is introduced. The actuators enable both heating and cooling to control a localized buoyancy while providing a substantial driving force to the system. Besides mimicking the locomotion, the bidirectional communication system enables the untethered delivery of commands to the underwater subject and real‐time acquisition of the robotic fish's physical information. Underwater imaging validates the fish's practical use as a drone, allowing for inspecting the aquatic environment that is not easily accessible to humans. Future work studies the operation of the robotic fish as a collective swarm to examine a broader range of the underwater area and conduct various strategic missions.

A versatile jellyfish-like robotic platform for effective underwater propulsion and manipulation

“…1B ; see the “Fabrication of the HASEL jellyfish robot” section in Materials and Methods). As a feasible improvement in future development, an active buoyance control unit, e.g., using thermally actuated liquid-gas phase transitions ( 3 , 35 , 36 ), can be incorporated into the platform to assist even more agile locomotion and various functions of the robot. For example, the buoyancy could be notably increased when the unit’s volume is enlarged by heating the low–boiling point liquid inside, which can increase the buoyancy and enhance the upward propulsion and transportation of the objects.…”

“…One possible solution would be to separate the grippers from the propellers, place them on the bottom, and use all six lappets as propellers to enhance the thrust. Second, practical approaches from other established research fields, such as buoyancy-tunable mechanisms ( 11 , 35 , 36 ) , could be incorporated into our platform for much enhanced loading-carrying capability. For example, after the robot approaches the targeted location efficiently and grasps the objects, inflation of the buoyancy-tunable unit by heating up the low–boiling point liquid inside can notably increase the buoyancy force for the effective upward transportation of real-world trash.…”

Actuation for flexible and stretchable microdevices

“…80 In addition, thermo-pneumatic actuation uses the expansion of gas, 81 or a change in the volume of liquid or solid in a confined space under heat input. 106 The phase change happens with liquid evaporating into gas 76,107 or solid melting into liquid, resulting in considerable volume expansion. This phenomenon increases pressure to deflect the flexible walls of the confined space and do external work on the environment.…”

“…This phenomenon increases pressure to deflect the flexible walls of the confined space and do external work on the environment. The actuating flexible structures can be in the form of membranes, 108 inflatable chambers, 76,107 or bellows, 81 where the surrounding walls deflect to create the actuation. Yoon et al 76 reported a phase change soft actuator capable of bi-directional operation by thermoelectric heating and cooling.…”

Multicomponent and multifunctional integrated miniature soft robots

“…Yoerger et al proposed marine robots capable of tracking the movements of jellyfish and larvae at depths of 200 m. 81 Inspired by marine vertebrates, Lee et al developed a flatfish-like robot that can be controlled by soft thermoelectric pneumatic actuators and can move freely in three dimensions in the water. 82 Small-scale biohybrid robots have been proven to be able to complete locomotion modes such as crawling, rolling, and swimming, but scaling up the biohybrid robots, such as mass fabrication of biohybrid robots beyond the centimeter level, remains challenging. 83 Further research in terms of tissue survival, the interaction of biological interfaces and the control methods of biological tissues are still needed.…”