Locomotion of Miniature Soft Robots

Abstract

as prospective aerial vehicles that can significantly enhance the efficiency of search-and-rescue missions, [16][17][18] perform dangerous operations in hazardous environments, [18] and function as miniature nodes in sensor networks. [18] Because miniature robots are expected to operate in various types of environments, it is essential for them to possess effective locomotive gaits to navigate well in such terrains. [19,20] This will be especially true if the robots have to negotiate across highly unstructured environments such as within the human body or at disaster sites. [5,10,21,22] Of the miniature robots, the soft robots are significantly more promising than their rigid counterparts in developing dexterous gaits because their degrees of freedom and adaptability are considerably higher. [23][24][25] By having the ability to generate a series of time-varying shapes, miniature soft robots have shown to be able to perform various types of locomotion, which allow them to negotiate across complicated obstacles in their environments. [19,26] In addition to using such locomotion for navigation purposes, these gaits could also be beneficial for studying the locomotion of various small organisms. [4,13] In this report, we review the locomotion producible by miniature soft robots. The scope of this report is therefore different from reviews and commentaries that focus on the actuation, [3] applications, [2,21] or design [27] of miniature soft robots. It is also significantly different from reviews that focus on the applications of miniature robots, [1,10,11] and others that review the general principles [24,[28][29][30][31][32][33][34][35] or locomotion [34,36,37] of macro-scale soft robots. To facilitate our discussion, here we categorize the locomotion of the miniature soft robots into terrestrial, aquatic, and aerial locomotion (Figure 1). Under each category, we will highlight their key advancements, as well as their open challenges and future outlook. Except for the aerial robots that are in the centimeter-scale, our discussions will focus on soft robots that are in the micro/millimeter length scales. It is noteworthy that the discussions in this report will be restricted to synthetic materials. For miniature bio-robots based on natural materials, interested readers may refer to other reviews on biomolecular, biohybrid actuation, or microorganism-driven systems. [38][39][40][41][42][43] The report is organized as follows: Section 2 provides a brief discussion about the general actuation principles of miniature soft robots. This is followed by Sections 3-5 in which we discuss the advancements of miniature soft robots in their Miniature soft robots are mobile devices, which are made of smart materials that can be actuated by external stimuli to realize their desired functionalities. Here, the key advancements and challenges of the locomotion producible by miniature soft robots in micro-to centimeter length scales are highlighted. It is highly desirable to endow these small machines with dexterous locomotive gaits a...

A Tissue Adhesion‐Controllable and Biocompatible Small‐Scale Hydrogel Adhesive Robot

“…Small-scale wireless medical robots have been recently proposed to carry out a targeted and minimally invasive drug delivery and treatment of diseases in the given local site of the body, without a surgical operation, [1][2][3][4][5][6][7][8] which would have a disruptive positive impact on healthcare. They can navigate within the body in a controlled way using medical imaging feedback, and conduct medical tasks, such a drug delivery, hyperthe body but also damage to the tissue.…”

Magnetic Miniature Actuators with Six‐Degrees‐of‐Freedom Multimodal Soft‐Bodied Locomotion

“…Rolling could be considered as one of the fastest modes of terrestrial locomotion. [ 6,10 ] Our proposed MMR could execute this locomotion by first applying a of along its positive ‐axis so that it could assume a “U”‐shaped configuration ( Figure A). It is advantageous to adopt such a configuration because this would be a favorable shape for the MMR to roll.…”

“…Similar to undulating crawling, jumping would be an effective locomotion for the MMR to overcome difficult obstacles. [ 6,10 ] Specifically, MMRs could execute such locomotion to jump across barriers that had heights greater than their body length. [ 6,10 ] The jumping locomotion could be executed by first deforming the proposed actuator into a “U”‐shaped configuration (the applied was along ‐axis with a magnitude of ) and then orientating the MMR's plane such that its ‐axis had a clockwise angle away from the vertical upright direction.…”

The ultrafast snap of a finger is mediated by skin friction

“…For soft robotics, achieving realistic models of friction dynamics has been identified as an avenue for improving the manipulative capabilities of robotic systems [42,43]. Thus, our work has potential to contribute to a growing body of bioinspired latches where robust modulating ability of frictional latches can enhance and pave new functionalities in soft robots [32,44,45].…”