Recent research on robotic fish mainly focused on the bionic structure design and realizing the movement with smart materials. Although many robotic fish have been proposed, most of these works were oriented toward shallow water environments and are mostly built with purely rigid structures, limiting the mobility and practical usability of robotic fish. Inspired by the stability of the real manta ray, a manta ray robot design is proposed with soft material made flapping wing based on an open-source ROV (Remotely Operated Vehicle). The flapping wing structure with three different materials mimics the wide pectoral fins of real manta rays, which have bones, muscles, and skin. Furthermore, its modular design makes it easy to install and disassemble. The kinematic and hydrodynamic analysis of the manta ray robot are simulated in this paper. The actual manta ray robot is fabricated and several sets of test are performed in the pool. The robot can swim forward continually and stably with a simple rolling and pitching pattern.

As underwater missions become more and more complex, novel underwater manipulators with better performance are demanding. Soft underwater manipulators are judged to be the development direction and expected to have better performance in safe and compliant interaction with the target in underwater operations such as biological sampling. This paper provides an overview on the state-of-the-art of both hard and soft underwater manipulators to give a prospect for soft underwater manipulators. Key technologies in the design of soft underwater manipulators are identified, including the configuration design, actuator design and stiffening design of them.

Pneumatically actuated soft robots have attracted significant attention in recent years due to their non-linear structures for performing biomimetic motions to enhance human-machine interactions. However, manufacturing soft robots, especially those featuring complex 3D structures, still faces significant challenges as traditional lithography-based micro/nanofabrication technologies have some limitations, such as limited material choices and layer-by-layer architectures. In this work, a facile multi-material jointed direct ink writing (MJDIW) printing method is introduced. In comparing with the traditional micro/nanofabrication and other additive manufacturing methods, the method enables truly freeform 3D printing to fabricate entirely soft actuators and robots with complex 3D structures, while integrating materials with different mechanical characteristics to expand the manufacturing capabilities of additive manufacturing methods. The material properties and printing parameters, and conducted finite element analysis (FEA) is systematically investigated to provide the general design guidelines through simulating actuator motions. Several actuators such as linear elongation and bending actuators are manufactured either by employing a single material or multiple materials with different mechanical properties. Finally, a multi-directional soft manipulator with complex internal channels is printed using different materials to illustrate the versatility of the printing methods.