Abstract
In recent years, jointless soft robots have demonstrated various curvilinear motions unlike conventional robotic systems requiring complex mechanical joints and electrical design principles. The materials employed to construct soft robots are mainly programmable anisotropic polymeric materials to achieve contactless manipulation of miniaturized and lightweight soft robots through their anisotropic strain responsivity to external stimuli. Although reviews on soft actuators are extensive, those on untethered soft robots are scant. In this study, we focus on the recent progress in the manipulation of untethered soft robots upon receiving external stimuli such as magnetic fields, light, humidity, and organic solvents. For each external stimulus, we provide an overview of the working principles along with the characteristics of programmable anisotropic materials and polymeric composites used in soft robotic systems. In addition, potential applications for untethered soft robots are discussed based on the physicochemical properties of programmable anisotropic materials for the given external stimuli.
Highlights
Soft robots implement facile curvilinear motions and various functions including bending, twisting, and folding without employing numerous rigid joints
Untethered soft robotic systems provide a high degree of freedom for motility by removing limitations of working distance and complexity of motion originating from distance and wire tangling, respectively
The programmed film was folded to form a tube-like geometry through the swelling properties of the hydrogel polymer, resulting in radial alignments of magnetic particles
Summary
Soft robots implement facile curvilinear motions and various functions including bending, twisting, and folding without employing numerous rigid joints. To achieve untethered manipulation of miniaturized soft robots, diverse anisotropic materials and composites have been investigated for stimuli-responsive motility using magnetic fields [1,2,3,4,5,6,7,8,9,10,11], light [12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27], organic solvents [28,29,30,31,32,33,34,35,36,37,38], and chemical reactions [39,40,41,42,43]. Motile strategies to achieve magnetic maneuvers have been widely developed by programming (i) the geometry of robots, (ii) the
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