The ocean environment has enormous uncertainty due to the influence of complex waves and undercurrents. The human beings are limited in their abilities to detect and utilize marine resources without powerful tools. Soft robots employ soft materials to simplify the complex mechanical structures in rigid robots and adapt their morphology to the environment, making them suitable for performing some challenging tasks in place of manual labor. Due to superior flexible and deformable bodies, underwater soft robots have played significant roles in numerous applications in recent decades. Meanwhile, various technical challenges still need to be tackled to ensure the reliability and practical performance of underwater soft robots in complicated ocean environment. Nowadays, some researchers have developed underwater soft robotic systems based on biomimetics and other disciplines, aiming at comprehensive exploration of ocean and appropriate utilization of unexploited resources. This review presents the recent advances of underwater soft robots in the aspects of intelligent soft materials, fabrication, actuation, locomotion patterns, power storage, sensing, control, and modeling; additionally, the existing challenges and perspectives are analyzed as well.

This paper presents the development of 3D-printed micro force sensors with micronewton sensing resolutions. Two representative 3D printing techniques, fused deposition method (FDM) and stereolithography (SLA), are utilized to establish polymeric micro sensor structures with a resolution down to 300 μm. Two types of 3D-printed strain-gauge force sensors have been designed aiming at different force measurement ranges (0-2.5 mN and 0-120 mN) with micronewton force sensing resolutions (4.3 μN and 56 μN, respectively). As a proof-of-concept demonstration, the two 3D-printed force sensors are used in custom-made mechanical characterization systems for measuring Young’s moduli of polydimethylsiloxane (PDMS) samples at different crosslinking levels. The experimental technique presented here could empower rapid prototyping of high-performance force sensors utilizing consumer-level 3D printers, and will significantly boost the flexible design and customization of force-sensing systems with a variety of design requirements.