Bioinspired soft robots for deep-sea exploration

Abstract

The deep ocean, Earth's untouched expanse, presents immense challenges for exploration due to its extreme pressure, temperature, and darkness. Unlike traditional marine robots that require specialized metallic vessels for protection, deep-sea species thrive without such cumbersome pressure-resistant designs. Their pressure-adaptive forms, unique propulsion methods, and advanced senses have inspired innovation in designing lightweight, compact soft machines. This perspective addresses challenges, recent strides, and design strategies for bioinspired deep-sea soft robots. Drawing from abyssal life, it explores the actuation, sensing, power, and pressure resilience of multifunctional deep-sea soft robots, offering game-changing solutions for profound exploration and operation in harsh conditions.

Fig. 1. Evolutionary design of deep-sea soft machines.

a Pressure-resistant designs such as pressure vessels are widely used to protect the mechatronics in deep-sea rigid robots. Reproduced with permission from ref. , copyright 2021, The American Association for the Advancement of Science. b Deep-sea snailfish possess remarkable adaptability and survivability under harsh deep-sea conditions. Their distributed skulls and muscle actuation provide abundant bioinspiration for designing multifunctional deep-sea soft machines. Reproduced with permission under CC BY 4.0 license from ref. . c Soft robots are mainly composed of elastic materials and can generate muscle-like actuation for various tasks such as swimming. Reproduced with permission from ref. , copyright 2018, The American Association for the Advancement of Science. Previous demonstrations of deep-sea soft robots include: d A dexterous soft manipulator that integrates bending, rotary, and grasping units for deep-sea manipulation; Reproduced with permission under CC BY 4.0 license from ref. . e–g Soft robotic grippers perform delicate collection of fragile deep-sea specimens at depths of 800 m, 843 m and 1800 m, respectively; e–g Reproduced with permission under CC BY 4.0 license from refs. ^–. h A soft jamming gripper was field-tested at a depth of 1200 m; Reproduced with permission from ref. , copyright 2017, Mary Ann Liebert, Inc. i A deep-sea soft gripper was integrated with a waveguide-based tactile sensor; Reproduced with permission from ref. , copyright 2018, IEEE. j A bioinspired soft robot that is able to operate at a depth of 10,900 m^,. Reproduced with permission from ref. , copyright 2021, Springer Nature.

Fig. 2. Bioinspired deep-sea soft actuation.

a Deep-sea invertebrate (e.g., sea anemones, octopuses) achieve actuation and various movements (e.g., manipulation) using their hydrostatic skeletons and muscular hydrostats, which inspire the design of (b) a hydraulic jamming gripper for implementing universal deep-sea grasping and a dexterous soft manipulator. c Deep-sea vertebrates utilize the contraction and expansion of their muscles attached to the skeleton to generate a driving force for locomotion. Reproduced with permission from ref. , copyright 2021, Springer Nature. d When a voltage is applied on a DEA membrane, the induced electrostatic force leads to a decrease in its thickness and an expansion in its area, which has been utilized in the flapping actuation of deep-sea soft robot. Reproduced with permission from ref. , copyright 2021, Springer Nature. e The sperm whale achieves buoyancy control by regulating the liquid-solid phase change of its spermaceti organ. f Inspired by the phase-change mechanism of the spermaceti organ, soft actuators integrating phase-change materials have the potential to be used for lightweight actuation under pressure conditions. Reproduced with permission under CC BY 4.0 license from ref. .

Fig. 3. Pressure-resilient design of bioinspired deep-sea soft robots.

a As a deep-sea animal with an endoskeleton, the snailfish possesses a low modulus internal skeleton and a distributed skull in its soft tissue. b, c Despite experiencing the same value of hydrostatic pressure, the maximum shear stress on the distributed skulls of the snailfish is significantly lower than that of the stickleback fish from shallow water. d, e The distributed skulls of snailfish serve as inspiration for the design of detaching electronics, which enhances their pressure resilience in the deep sea. Reproduced with permission from ref. , copyright 2021, Springer Nature.

Fig. 4. Bioinspired deep-sea soft sensing.

a Many deep-sea creatures such as tripod fish have evolved long appendages to enhance their tactile sensitivity, which has inspired the design of (b) waveguide deep-sea tactile sensor. Reproduced with permission from ref. , copyright 2018, IEEE. c Benthobatis moresbyi have special organs to emit electric field and electroreceptor arrays to detect its surrounding objects. d The electric sensory organs of deep-sea fish inspire the potential design and integration of flexible electroreceptor array for electrolocation of soft machines. Reproduced with permission under CC BY-NC 4.0 license from ref. . e Cetaceans detect surrounding objects using echolocation in darkness, inspiring (f) a flexible acoustic transceiver composed of piezoelectric electrodes attached to a flexible substrate for potential distance communication and sensing of deep-sea soft robot^,. Reproduced with permission under CC BY 4.0 license from ref. .

Fig. 5. Perspective design and practical application of future deep-sea soft robots.

a By integrating soft electrostatic hydraulic actuation, soft sensory arrays, embodied energy regeneration skins, and flexible onboard processing electronics, future deep-sea soft robots could enable long-endurance and more autonomous machine behaviors in deep-sea tasks. Reproduced with permission under CC BY 4.0 license from ref. . b Bioinspired soft robots will enable scientists to perform in situ investigations of the deep-sea habitats, and to preserve the original deep-sea ecosystem.