# Actuation Mechanisms and Applications for Soft Robots: A Comprehensive Review
## 3 Applications
### Bionic and Motion  
Bionic and motion are the basic applications of soft robots. Inspired by observations of animals' body structures, muscles, and bones, researchers designed bionic soft robots to mimic crawling, jumping, and rolling [14]. Biomimetic objects are generally creatures with simple movement processes that are easy to imitate, such as inchworms, caterpillars,jellyfish, and octopuses. In this way, soft robots can use flexible structures to move in natural environments and quickly adapt or interact with the environments [62].  
A type of soft robot can be designed according to the working principle of an inchworm [81]. The inchworm utilises the stretching of abdominal muscles to drive the front and rear legs to cyclically grasp and move to achieve an \(\Omega\)-shaped continuous crawling motion. The used materials are required to be soft and deformable, and the driving method generally adopts SMA and EAP. When an electric current is applied, the actuating material deforms, mimicking the alternating movement of the front and back legs of the inchworm. SMA wires are longitudinally embedded in a soft polymer to mimic the longitudinal muscle fibers that control the abdominal contraction of the inchworm during movement. Another example is a DEA-driven bionic inchworm robot, which uses reinforcing fibers to suppress the deformation of the dielectric elastomer in other directions [166]. The deformation and bending of the dielectric elastomer can be effectively converted into forward motions. This robot's average speed can reach 1.1 mm/s, and each motion cycle can advance 3.8 mm.  
A type of soft robot can be designed according to the working principle of a caterpillar. This kind of bionic robot simulates the crawling action of caterpillars by driving friction between the moving body and the ground. The materials used are generally polymers, and the actuation methods include fluid, light, and electromagnetic methods. [PERSON] et al. designed a robot driven by pneumatic actuators. The biological structure and morphological movement of caterpillars are simulated by the synergistic movement of the deformation of the bellows body and the friction feet. The robot can move at a speed of 1.05 cm/s (0.16 body length per second) [167]. A light-driven bionic caterpillar robot realises rubbing motion by light-induced deformation of heated liquid crystal elastomers [23]. This robot can adapt to various unstructured environments, and its movement speed can reach 0.25 mm/s.  
A type of soft robot can be designed according to the working principle of a jellyfish. A jellyfish swims by contracting and expanding epidermal muscle fibers as well as the thrust of water currents. Researchers used elastic polymers to mimic the muscle fibers of jellyfish. By applying an electric current or changing the internal pressure, the polymer is deformed to simulate the swimming of the jellyfish. [PERSON] et al. used DEA materials to imitate the epidermal muscle fibers of jellyfish, and employed fluid electrodes to apply voltage and deform them, so the average swimming speed of such a designed robot could reach 3.2 mm/s, and it could work underwater silently [35].  
A type of soft robot can be designed according to the working principle of an octopus. The arms of octopuses can achieve some fine and complex movements by changing the shape of the arms by shortening, elongating, bending, twisting, and deforming the bodies of octopuses [14]. It can change the shape of the bionic octopus robot and grasp objects by using elastic polymers to simulate the muscles of octopus brachiopods and drive them with fluids or electric currents. For instance, a robotic arm was designed to mimic octopus brachiopods with embedded cables that replicate the function of octopus brachiopod muscles for propulsion and object grasping [168].