A Review of Soft Robots <s> Power Sources <s> Octopuses are molluscs that belong to the group Cephalopoda. They lack joints and rigid links, and as a result, their arms possess virtually limitless freedom of movement. These flexible appendages exhibit peculiar biomechanical features such as stiffness control, compliance, and high flexibility and dexterity. Studying the capabilities of the octopus arm is a complex task that presents a challenge for both biologists and roboticists, the latter of whom draw inspiration from the octopus in designing novel technologies within soft robotics. With this idea in mind, in this study, we used new, purposively developed methods of analysing the octopus arm in vivo to create new biologically inspired design concepts. Our measurements showed that the octopus arm can elongate by 70% in tandem with a 23% diameter reduction and exhibits an average pulling force of 40 N. The arm also exhibited a 20% mean shortening at a rate of 17.1?mm s?1?and a longitudinal stiffening rate as high as 2 N (mm s)?1. Using histology and ultrasounds, we investigated the functional morphology of the internal tissues, including the sinusoidal arrangement of the nerve cord and the local insertion points of the longitudinal and transverse muscle fibres. The resulting information was used to create novel design principles and specifications that can in turn be used in developing a new soft robotic arm. <s> BIB001 </s> A Review of Soft Robots <s> Power Sources <s> An important trend in electronics involves the development of materials, mechanical designs and manufacturing strategies that enable the use of unconventional substrates, such as polymer films, metal foils, paper sheets or rubber slabs. The last possibility is particularly challenging because the systems must accommodate not only bending but also stretching. Although several approaches are available for the electronics, a persistent difficulty is in power supplies that have similar mechanical properties, to allow their co-integration with the electronics. Here we introduce a set of materials and design concepts for a rechargeable lithium ion battery technology that exploits thin, low modulus silicone elastomers as substrates, with a segmented design in the active materials, and unusual ‘self-similar’ interconnect structures between them. The result enables reversible levels of stretchability up to 300%, while maintaining capacity densities of B1.1 mAh cm � 2 . Stretchable wireless power transmission systems provide the means to charge these types of batteries, without direct physical contact. <s> BIB002 </s> A Review of Soft Robots <s> Power Sources <s> Conventionally, engineers have employed rigid materials to fabricate precise, predictable robotic systems, which are easily modelled as rigid members connected at discrete joints. Natural systems, however, often match or exceed the performance of robotic systems with deformable bodies. Cephalopods, for example, achieve amazing feats of manipulation and locomotion without a skeleton; even vertebrates such as humans achieve dynamic gaits by storing elastic energy in their compliant bones and soft tissues. Inspired by nature, engineers have begun to explore the design and control of soft-bodied robots composed of compliant materials. This Review discusses recent developments in the emerging field of soft robotics. <s> BIB003
A suitable power source for soft robots actuation must be stretchable and portable BIB003 . For pneumatic actuators, existing fluidic power sources are not soft and are usually big and bulky. Most of the current off the-shelf pressure sources are generally limited to compressors or pumps and compressed air cylinders [16] . Drawing analogy from electrical systems, compressors are like generators as they convert electrical energy into mechanical energy, and compressed gas cylinders are similar to capacitors as they store a pressurized fluid in a certain volume to be discharged when required BIB003 . It is worth stating that electrically powered actuators as well as the electrical controllers for pneumatic systems require soft, flexible, lightweight electrical power sources BIB002 . As with soft electronics, this is an area of research that is being currently explored BIB003 . states BIB003 a. Longitudinal tensile actuators (e.g. tension cables or shape memory alloy actuators which contract when heated) along a soft robot arm cause bending when activated. b. Transverse tensile actuators cause a soft robot arm to extend when contracted (a muscle arrangement also seen in the octopus72). c. Pneumatic artificial muscles composed of an elastomeric tube in a woven fibre shell. A pressure applied internally causes the tube and shell to expand radially, causing longitudinal contraction. d. Fluidic elastic actuator or Pneu-Net design consisting of a pneumatic network of channels in an elastomer that expand when filled with a pressurized fluid, causing the soft body to bend toward a strain limited layer (e.g. a stiffer rubber or elastomer embedded with paper or other tensile fibres Resting state Actuated state Figure 3 : Octopus-inspired manipulation BIB001 2.6 Modelling and Kinematics As earlier noted, a novel algorithm is required for soft robots as the traditional robots' approach is incompatible with it. In the same vein, the kinematics and dynamics of soft robotic systems differs from those of traditional, rigid-bodied robots BIB003 . Since its composition is made up of series of actuation elements, these robots approach a continuum behaviour [ibid] . In theory, the final shape of the robot can be described by a continuous function and modelling this behaviour requires continuous mathematics [ibid] .  cited in BIB003 noted that researchers have developed new static, dynamic and kinematic models that capture soft robots' ability to bend and flex. This has motivated development of new algorithms and techniques in the aspect of its actuation, sensing, computation as well as power sources and kinematics modelling. This is necessary as the approach and algorithm of traditional robots is incompatible with soft robots. Soft robots have the capability to operate in complex and unstructured environment due to their inherent potential to exploit morphological computation to adapt to, and interact with, the world in a way that is difficult or impossible with rigid systems. They could be employed in search and rescue operations in a natural disaster relief effort, and of interest is their ability to interact with people without causing injury especially in the field of medical care as seen in personal robots.