TheMariana Trench is the deepest part of the Earth. Without a pressure-resilient“armor”, a man-made machine would be destroyed by the overwhelminglyhydrostatic pressure if it were to venture into this uninhabitable territory.However, deep-sea creatures can thrive at extreme depths thanks to their uniqueanatomies. If we can draw inspiration from deep-sea creatures, converting the“secret of life” into the “power of machinery”, we will be able to developintelligent machines that can adapt themselves to complex environments, thuspromoting the exploration of deep seas.

Theresearch team led by Prof. LI Tiefeng from the Center for X-Mechanics at theZhejiang University School ofAeronautics and Astronautics and Zhejiang Lab conductedinter-disciplinary research with its partners and pioneered in proposing theprinciple of pressure adaptation in mechatronic systems. They developed anuntethered bio-inspired soft robot for deep-sea exploration, with onboardpower, control and actuation protected from pressure by integrating electronicsin a silicone matrix. This self-powered robot can successfully eliminate therequirement for any rigid vessel.

Theirresearch findings were published as a cover story entitled “Self-poweredsoft robot in the Mariana Trench” in Nature on March 4.

Inspirationfrom a snailfish

Biologicalstudies have found that hundreds of species live at depths ranging between6,000 meters and 11,000 meters in the Mariana Trench and the snailfish is oneof them.

Howstrong is the pressure at a depth of 10,000 meters in the deep sea? “At the bottomof the 10,900-meter-deep sea, the hydrostatic pressure is about 110 MPa. Todraw a less appropriate analogy, it is equivalent to a one-ton-heavy carimposed on the tip of a finger. In the past, rigid vessels orpressure-compensation systems were required to overcome the extremely highpressure in the deep sea, thus able to protect mechatronic system,” said LITiefeng.

Thesoft robot developed by LI Guorui (the first author) et al. exhibits remarkableswimming performance due to its soft actuator, including dielectric elastomers(DEs) and flapping fins. The electronics, including a battery and amicrocontrol unit (MCU), are encapsulated in a silicone soft body. To enhancepressure resilience, researchers mitigated the shear stress by using adecentralized design in which the components are wire-connected with orseparated onto several smaller printed circuit boards.

Thesoft robot bears a striking resemblance to a snailfish in appearance. It is 22centimeters long and 28 centimeters in wingspan. To achieve a highly-adaptive,pressure-resilient and structurally complete soft robot, researchers adopted analternative approach. Samples of snailfish collected by the research team ledby HE Shunping from the CAS Institute of Deep Sea Science and Engineering inthe Mariana Trench also provided inspiration for the design of the soft robot.

Thisfish is marked by a distributed skull and flapping pectoral fins, which enableit to live in high-pressure environments.

Researchersmanaged to improve the pressure resilience of the electronic components andsoft actuators, thereby enabling the whole system to adapt to high pressures inthe deep sea without any rigid vessel. “We aim to build small-sized, ductileand intelligent deep sea robots so as to reduce the difficulty and cost ofdeep-sea exploration,” said LI Guorui in Zhejiang Lab.

TheDE muscle

Theflapping fins (each with two DE membranes) of the soft robot are powered by thecompact high-voltage amplifier. To swim freely, the soft robot should also beable to deal with the problem with reduced power at low temperatures and highpressures in the deep sea. The research team led by LUO Yingwu from theZhejiang University College of Chemical and Biological Engineering developedself-powered DE muscle which can adapt to extreme temperatures. It can functionproperly even in the Mariana Trench (at approximately 110 MPa and 0~4°C). TheDE muscle is another major breakthrough of this research.

Toachieve the fluttering of the fins, researchers ingeniously used the seawateroutside the DE muscle as negative charges. When a high voltage was applied,positive and negative charges would accumulate on the opposite sides of the DEmuscle. The deformation of polymer membranes could thus generate the flappingmotion of the fins for propulsion.

Multidisciplinarysynergy

“Mechanicsis an ancient and traditional discipline. This research mirrors the criticalrole of X-mechanics in multi-disciplinary research and it is the outcome ofcooperation among researchers with different academic backgrounds and technicalspecialties.” In addition to research teams from the Zhejiang University Schoolof Aeronautics and Astronautics and Zhejiang Lab, researchers from colleges andschools at Zhejiang University, including the School of Mechanical Engineering,the College of Energy Engineering, the College of Chemical and BiologicalEngineering and the Ocean College, and the CAS Institute of Deep Sea Scienceand Engineering, participated in this project.

Inthis work, researchers verified the feasibility of materials and structuresthrough a large quantity of simulation experiments in high-pressureenvironments. This soft robot experimentally proved to work properly in harshand special environments, including deep seas, polar regions and high-impactareas.

Thiswork will largely promote the research progress of deep-sea robotics. “Thisresearch opens up a new channel for deep-sea explorations and environmentalobservations, and is expected to improve the application capability of deep-seaintelligent devices and robots in multiple tasks and complex scenarios,” saidLI Tiefeng.