A Review of Soft Robots <s> Introduction <s> Traditional robots have rigid underlying structures that limit their ability to interact with their environment. For example, conventional robot manipulators have rigid links and can manipulate objects using only their specialised end effectors. These robots often encounter difficulties operating in unstructured and highly congested environments. A variety of animals and plants exhibit complex movement with soft structures devoid of rigid components. Muscular hydrostats e.g. octopus arms and elephant trunks are almost entirely composed of muscle and connective tissue and plant cells can change shape when pressurised by osmosis. Researchers have been inspired by biology to design and build soft robots. With a soft structure and redundant degrees of freedom, these robots can be used for delicate tasks in cluttered and/or unstructured environments. This paper discusses the novel capabilities of soft robots, describes examples from nature that provide biological inspiration, surveys the state of the art and outlines existing challenges in soft robot design, modelling, fabrication and control. <s> BIB001 </s> A Review of Soft Robots <s> Introduction <s> This paper reviews various processes for manufacturing new type of robots termed “soft biomimetic robots.” Most robots are made of rigid metallic materials. But in recent years, various biomimetic robots based on soft materials and compliant parts have been developed. New manufacturing processes are required to fabricate these types of robots, and the processes include Shape Deposition Manufacturing (SDM) and Smart Composite Microstructures (SCM). Since the design of robots are limited by the available material and manufacturing processes, it is important to develop new manufacturing processes that will enable development of novel soft biomimetic robots. In this paper, various manufacturing processes which can be applied to soft robot fabrication are summarized, and features of those processes are described. Processes are divided into three categories; soft robot body fabrication, actuators for soft robots and stretchable electronics. This review provides a guideline for selecting manufacturing processes for soft robots and developing new processes that will enable new type of robots to be designed. <s> BIB002 </s> A Review of Soft Robots <s> Introduction <s> Animals exploit soft structures to move effectively in complex natural environments. These capabilities have inspired robotic engineers to incorporate soft technologies into their designs. The goal is to endow robots with new, bioinspired capabilities that permit adaptive, flexible interactions with unpredictable environments. Here, we review emerging soft-bodied robotic systems, and in particular recent developments inspired by soft-bodied animals. Incorporating soft technologies can potentially reduce the mechanical and algorithmic complexity involved in robot design. Incorporating soft technologies will also expedite the evolution of robots that can safely interact with humans and natural environments. Finally, soft robotics technology can be combined with tissue engineering to create hybrid systems for medical applications. <s> BIB003 </s> A Review of Soft Robots <s> Introduction <s> The remarkable advances of robotics in the last fifty years, which represent an incredible wealth of knowledge, are based on the fundamental assumption that robots are chains of rigid links. The use of soft materials in robotics, driven not only by new scientific paradigms (biomimetics, morphological computation, and others), but also by many applications (biomedical, service, rescue robots, and many more), is going to overcome these basic assumptions and makes the well-known theories and techniques poorly applicable, opening new perspectives for robot design and control.The current examples of soft robots represent a variety of solutions for actuation, and control. Though very first steps, they have the potential for a radical technological change. Soft robotics is not just a new direction of technological development, but a novel approach to robotics, unhinging its fundamentals, with the potential to produce a new generation of robots, in the support of humans in our natural environments. <s> BIB004 </s> A Review of Soft Robots <s> Introduction <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> BIB005 </s> A Review of Soft Robots <s> Introduction <s> Roboticists have begun to design biologically inspired robots with soft or partially soft bodies, which have the potential to be more robust and adaptable, and safer for human interaction, than traditional rigid robots. However, key challenges in the design and manufacture of soft robots include the complex fabrication processes and the interfacing of soft and rigid components. We used multimaterial three-dimensional (3D) printing to manufacture a combustion-powered robot whose body transitions from a rigid core to a soft exterior. This stiffness gradient, spanning three orders of magnitude in modulus, enables reliable interfacing between rigid driving components (controller, battery, etc.) and the primarily soft body, and also enhances performance. Powered by the combustion of butane and oxygen, this robot is able to perform untethered jumping. <s> BIB006 </s> A Review of Soft Robots <s> Introduction <s> The proliferation of soft robotics research worldwide has brought substantial achievements in terms of principles, models, technologies, techniques, and prototypes of soft robots. Such achievements are reviewed here in terms of the abilities that they provide robots that were not possible before. An analysis of the evolution of this field shows how, after a few pioneering works in the years 2009 to 2012, breakthrough results were obtained by taking seminal technological and scientific challenges related to soft robotics from actuation and sensing to modeling and control. Further progress in soft robotics research has produced achievements that are important in terms of robot abilities—that is, from the viewpoint of what robots can do today thanks to the soft robotics approach. Abilities such as squeezing, stretching, climbing, growing, and morphing would not be possible with an approach based only on rigid links. The challenge ahead for soft robotics is to further develop the abilities for robots to grow, evolve, self-heal, develop, and biodegrade, which are the ways that robots can adapt their morphology to the environment. <s> BIB007
Traditional robots with rigid bodies and links are widely employed in manufacturing and could be coded to perform a specific task effectively and in most cases with certain adaptable constraints BIB005 . Essentially, traditional robots are built from non-complaint materials BIB002 and they are constructed mainly from hard materials such as aluminium and steel BIB006 . Due to inflexibility associated with the rigid links and joints of the robot, they are often unsafe to interact with human beings BIB005 . In a bid to reduce the related risks while working with traditional robots, the human and robotic workspaces in an industrial environment are often separated [ibid] . The recent Soft robots provide an opportunity to bridge the gap between machines and people BIB004 . Generally, soft robots are biologically-inspired with inspiration garnered from different capabilities of living organisms such as climbing of geckos, wing flapping motion of butterflies and crawling motion of earthworms amongst others BIB003 . Soft robots are made from fluids, gels, soft polymers, and other easily deformable matter with little or no rigid material  . These materials exhibit similar elastic and rheological properties of soft biological matter and these allow the robot to be more versatile and robust to operate in a constrained environment and more so, for seamless human interaction [ibid] . However, [7] gave a different view on the definition of soft robot and claimed a "soft robot" is appropriately named when the stresses, it is subject to cause it to deform prior to damaging the class of objects for which it was designed. Concisely, a traditional robot could be thought as soft robot when interacting with a harder object, such as a diamond [ibid]. According to BIB004 , soft robotics could be viewed from two main perspectives which are distinguishable from each other. Firstly, the softness of a robot was seen intrinsically due to the features of the robot's body ware which would be the focus of this review BIB001 . Secondly, softness of a robot was viewed from the soft interaction provided when rigid links are used to control the actuator stiffness of the robot  . BIB007 noted that soft robotics was first used to describe robot with rigid links and mechanically complaints joints with variable stiffness. However, this would not be discussed in detail in this review. In the first approach, robots are made of soft materials and they undergo high deformations during interaction BIB001 . Soft actuators and materials which could vary in their stiffness are used in this method, and their control is partially embedded in the body morphology [ibid]. This approach exploited the material properties of the robot and its capacity to interact with the environment [ibid]. However, in the second approach, robots are built with traditional rigid links, but the control system varies the resistance that the robot has to exhibit when interacting with the environment, people and object in this case, either through compliance or impedance control schemes  . [1] and BIB004 further reiterated that soft robots use compliant material and are built using nontraditional manufacturing processes. Moreover, these robots integrate several parts such as actuators and sensors as well as computation amongst others [ibid] . As regards to the assembly process, joining between the materials are made by casting, laminating or adhesives as against the using of bolts and nuts in traditional robots BIB002 . More specifically, soft robots are viewed as biomimetic robots in that they mimic specific capabilities of certain organisms. However, it is worth noting that soft robots are different from previous biomimetic robots such as snake robots, humanoid robots and robotic fish that are built using traditional manufacturing processes [ibid]. This review of soft robots is organised into fundamentals of soft robots, manufacturing processes of soft robots as well as application of soft robots and its limitations. 1