Soft Robotics Across Scales: Fundamentals to Applications

Abstract

As the name suggests, soft robots are recognized by their active “deformability” and passive “compliance”. In comparison with their rigid-bodied counterparts, soft robots exhibit a library of unique and attractive characteristics, such as the compliant interaction with the environment, the resistance to damages and wear, the shape-morphing capability, the abundant degrees of freedom (DOFs), the ability to be controlled by non-electric signals, and the suitability for batch fabrication and minimization. Research efforts have been devoted to this field and a large variety of intriguing soft robots have been proposed. Some examples are octopus-inspired soft arms, hand-like soft grippers, skin-mimicking soft electronics, and shape-morphing miniature robots. The recent emergence of novel soft materials and advanced fabrication techniques have spurred a new wave of rapid development of soft robots. In addition, the growing interest in miniaturized robots for healthcare, exploratory, and rescue applications has provided new opportunities to take good advantages of the traits of soft robots. Soft robots have become one of the most promising candidates to undertake the tasks at small size scales, where conventional mechanical components can no longer be utilized due to the difficulties in downscaling. In view of the entrancing potential of soft robots in addressing real-world challenges, we have organized this special issue to include high-quality research, review, and perspective articles that study soft robots with a characteristic length ranging from meter to centimeter, then further down to millimeter and micrometer. Most conventional rigid-bodied robots are at the meter size scale. In comparison, soft robots at this size scale excel as agile manipulators that could handle delicate and brittle objects, and also as an advantageous option to build safe interactions with humans. Hao et al. (doi: 10.1002/aisy.202300079) reported a tensegrity joint for low-inertia, compact, and compliant soft manipulators, aiming to reinforce the joint motion stability and enable self-contained sensing feedback. The proposed design avoids the requirement of complex kinematics modeling and sophisticated control model with sensing feedback. And the controller was trained with the proper joint configurations selected by a two-step sampling method. Soft robots at the centimeter size scale have a perfect size to go inside human body via natural orifices and ducts. They are small enough to access inner cavities in a minimally invasive manner, while at the same time they are also big enough to conduct meaningful interventional operations such as biopsy and drug delivery. Koszowska et al. (doi: 10.1002/aisy.202300062) reported a pair of independently actuated soft magnetic continuum manipulators for bimanual operations in the same confined anatomical cavities. The developed bimanual system was deployed in the confined anatomy of a skull-base phantom to simulate minimally invasive ablation of a pituitary adenoma. Zhang et al. (doi: 10.1002/aisy.202300325) reported a flexible biopsy robot with force sensing for deep lung examination. By cooperating with commercial bronchoscope, the proposed robot can reach narrow areas of the lung to perform biopsy operations. Soft robots at this size scale could also interact with organs or parts of human bodies. Lourdes et al. (doi: 10.1002/aisy.202200465) reported a magnetically actuated variable stiffness manipulator based on deployable shape memory polymer springs. Wang et al. (doi: 10.1002/aisy.202300127) reported a wearable glove with electrothermal-controlled lonogels for adhesive gripping. Centimeter size scale also corresponds to many fishes and insects we see in our daily lives. These animals demonstrate excellent capabilities in navigating in cluttered spaces and performing challenging functions. Intrigued researchers aim to mimic these capabilities using similar sized soft robots and harness them for transformative a