Soft robotic origami crawler

Oral administration microrobots for drug delivery

Oral administration is the most simple, noninvasive, convenient treatment. With the increasing demands on the targeted drug delivery, the traditional oral treatment now is facing some challenges: 1) biologics how to implement the oral treatment and ensure the bioavailability is not lower than the subcutaneous injections; 2) How to achieve targeted therapy of some drugs in the gastrointestinal tract? Based on these two issues, drug delivery microrobots have shown great application prospect in oral drug delivery due to their characteristics of flexible locomotion or driven ability. Therefore, this paper summarizes various drug delivery microrobots developed in recent years and divides them into four categories according to different driving modes: magnetic-controlled drug delivery microrobots, anchored drug delivery microrobots, self-propelled drug delivery microrobots and biohybrid drug delivery microrobots. As oral drug delivery microrobots involve disciplines such as materials science, mechanical engineering, medicine, and control systems, this paper begins by introducing the gastrointestinal barriers that oral drug delivery must overcome. Subsequently, it provides an overview of typical materials involved in the design process of oral drug delivery microrobots. To enhance readers' understanding of the working principles and design process of oral drug delivery microrobots, we present a guideline for designing such microrobots. Furthermore, the current development status of various types of oral drug delivery microrobots is reviewed, summarizing their respective advantages and limitations. Finally, considering the significant concerns regarding safety and clinical translation, we discuss the challenges and prospections of clinical translation for various oral drug delivery microrobots presented in this paper, providing corresponding suggestions for addressing some existing challenges.

Bio-inspired soft pneumatic actuator based on a kresling-like pattern with a rigid skeleton

INTRODUCTION

Biomimetic soft pneumatic actuators (SPA) with Kresling origami patterns have unique advantages over conventional rigid robots, owing to their adaptability and safety.

OBJECTIVES

Inspired by cloning and moving behaviors observed from salps, we proposed an SPA based on a Kresling-like pattern with a rigid skeleton. The elongation and output force were tested, and the effectiveness of the applications with the SPA was evaluated.

METHODS

The proposed SPA consists of rigid skeletons and a soft skin. The rigid skeletons are constructed using layers of Kresling-like patterns, while a novel extensible inserting structure is devised to replace the folds found in conventional Kresling patterns. This innovative approach ensures that the SPA exhibits axial contraction/expansion motion without any twisting movement. To mimic the bionic characteristics of swimming and ingesting progress of salps, the proposed SPA can perform an axial contraction motion without twisting and a controllable bending motion based on multi-layered Kresling-like patterns; to mimic the cloning and releasing life phenomena of salps, the number of layers of Kresling-like patterns is changeable by adding or reducing skeleton components according to the practical needs.

RESULTS

The experimental elongation results on the SPA with multiple layers of Kresling-like patterns show that the elongation can increase to above 162% by adding layers; the experimental output force results show that the three-layer SPA can provide 6.36 N output force at an air flow rate of 10 L/min, and the output force will continue to increase as the number of layers of Kresling-like pattern increases or the air flow rate increases. Further, we demonstrate the applications of the SPA in soft grippers, scissor grippers, claw grippers and pipe crawlers.

CONCLUSION

Our proposed SPA can avoid twisting in the radial contraction motion with high elongation and output force, and provide the practical guidance for bio-inspired soft robotic applications.

Liquid Crystal Elastomer-Liquid Metal Composite: Ultrafast, Untethered, and Programmable Actuation by Induction Heating

Liquid crystal elastomers (LCEs) are a class of stimuli-responsive materials that have been intensively studied for applications including artificial muscles, shape morphing structures, and soft robotics due to their capability of large, programmable, and fully reversible actuation strains. To fully take advantage of LCEs, rapid, untethered, and programmable actuation methods are highly desirable. Here, a liquid crystal elastomer-liquid metal (LCE-LM) composite is reported, which enables ultrafast and programmable actuations by eddy current induction heating. The composite consists of LM sandwiched between two LCE layers printed via direct ink writing (DIW). When subjected to a high-frequency alternating magnetic field, the composite is actuated in milliseconds. By moving the magnetic field, the eddy current is spatially controlled for selective actuation. Additionally, sequential actuation is achievable by programming the LM thickness distribution in a sample. With these capabilities, the LCE-LM composite is further exploited for multimodal deformation of a pop-up structure, on-ground omnidirectional robotic motion, and in-water targeted object manipulation and crawling.

Multimodal locomotion ultra-thin soft robots for exploration of narrow spaces

From power plants on land to bridges over the sea, safety-critical built environments require periodic inspections for detecting issues to avoid functional discontinuities of these installations. However, navigation paths in these environments are usually challenging as they often contain difficult-to-access spaces (near-millimetre and submillimetre-high gaps) and multiple domains (solid, liquid and even aerial). In this paper, we address these challenges by developing a class of Thin Soft Robots (TS-Robot: thickness, 1.7 mm) that can access narrow spaces and perform cross-domain multimodal locomotion. We adopted a dual-actuation sandwich structure with a tuneable Poisson's ratio tensioning mechanism for developing the TS-Robots driven by dielectric elastomers, providing them with two types of gaits (linear and undulating), remarkable output force ( ~ 41 times their weight) and speed (1.16 times Body Length/s and 13.06 times Body Thickness/s). Here, we demonstrated that TS-Robots can crawl, climb, swim and collaborate for transitioning between domains in environments with narrow entries.

Computational synthesis of locomotive soft robots by topology optimization

Locomotive soft robots (SoRos) have gained prominence due to their adaptability. Traditional locomotive SoRo design is based on limb structures inspired by biological organisms and requires human intervention. Evolutionary robotics, designed using evolutionary algorithms (EAs), have shown potential for automatic design. However, EA-based methods face the challenge of high computational cost when considering multiphysics in locomotion, including materials, actuations, and interactions with environments. Here, we present a design approach for pneumatic SoRos that integrates gradient-based topology optimization with multiphysics material point method (MPM) simulations. This approach starts with a simple initial shape (a cube with a central cavity). The topology optimization with MPM then automatically and iteratively designs the SoRo shape. We design two SoRos, one for walking and one for climbing. These SoRos are 3D printed and exhibit the same locomotion features as in the simulations. This study presents an efficient strategy for designing SoRos, demonstrating that a purely mathematical process can produce limb-like structures seen in biological organisms.

Origami-Enhanced Mechanical Properties for Worm-Like Robot

In recent years, the exploration of worm-like robots has garnered much attention for their adaptability in confined environments. However, current designs face challenges in fully utilizing the mechanical properties of structures/materials to replicate the superior performance of real worms. In this article, we propose an approach to address this limitation based on the stacked Miura origami structure, achieving the seamless integration of structural design, mechanical properties, and robotic functionalities, that is, the mechanical properties originate from the geometric design of the origami structure and at the same time serve the locomotion capability of the robot. Three major advantages of our design are: the implementation of origami technology facilitates a more accessible and convenient fabrication process for segmented robotic skin with periodicity and flexibility, as well as robotic bristles with anchoring effect; the utilization of the Poisson's ratio effect for deformation amplification; and the incorporation of localized folding motion for continuous peristaltic locomotion. Utilizing the high geometric designability inherent in origami, our robot demonstrates customizable morphing and quantifiable mechanical properties. Based on the origami worm-like robot prototype, we experimentally verified the effectiveness of the proposed design in realizing the deformation amplification effect and localized folding motion. By comparing this to a conventional worm-like robot with discontinuous deformation, we highlight the merits of these mechanical properties in enhancing the robot's mobility. To sum up, this article showcases a bottom-up approach to robot development, including geometric design, mechanical characterization, and functionality realization, presenting a unique perspective for advancing the development of bioinspired soft robots.

Programming Motion into Materials Using Electricity-Driven Liquid Crystal Elastomer Actuators

As thermally driven smart materials capable of large reversible deformations, liquid crystal elastomers (LCEs) have great potential for applications in bionic soft robots, artificial muscles, controllable actuators, and flexible sensors due to their ability to program controllable motion into materials. In this article, we introduce conductive LCE actuators using a liquid metal electrothermal layer and a polyethylene terephthalate substrate. Our LCE actuators can be stimulated at low currents from 2 to 4 A and produce a maximum work density of 9.4 k J ∕ m 3 . We illustrate the potential applications of this system by designing a palm-activated artificial muscle gripper, which can be used to grasp soft objects ranging from 5 to 55 mm in size, and even ring-shaped workpieces with precise external or internal support. Furthermore, inspired by the movement of fruit fly larvae, we designed a new soft robot capable of bioinspired crawling and turning by inducing anisotropic friction with an asymmetric design. Finally, we illustrate advanced motional control by designing an autonomously rotating wheel based on the asymmetric contraction of its spokes. To assist in the production of autonomously moving robots, we provide a thorough characterization of its motion dynamics.

Reconfigurable origami-inspired multistable metamorphous structures

Origami-inspired metamorphous structures can adjust their shapes and mechanical behaviors according to operational requirements. However, they are typically composed of nonrigid origami, where required facet deformation complicates actuation and makes them highly material dependent. In this study, we present a type of origami metamorphous structure composed of modular bistable units, each of which is a rigid origami. The elasticity within the origami creases and switching of mountain and valley crease lines enable it to have bistability. The resultant metamorphous structure has multistability, allowing it to switch among multifarious configurations with programmable profiles. This concept was validated by potential energy analysis and experiments. Using this concept, we developed a robotic limb capable of both lifting and gripping through configuration changes. Furthermore, we used the origami units to construct a metamaterial whose properties could change with the variation of configurations. These examples demonstrate the concept's remarkable versatility and potential for many applications.

Controlling the fold: proprioceptive feedback in a soft origami robot

We demonstrate proprioceptive feedback control of a one degree of freedom soft, pneumatically actuated origami robot and an assembly of two robots into a two degree of freedom system. The base unit of the robot is a 41 mm long, 3-D printed Kresling-inspired structure with six sets of sidewall folds and one degree of freedom. Pneumatic actuation, provided by negative fluidic pressure, causes the robot to contract. Capacitive sensors patterned onto the robot provide position estimation and serve as input to a feedback controller. Using a finite element approach, the electrode shapes are optimized for sensitivity at larger (more obtuse) fold angles to improve control across the actuation range. We demonstrate stable position control through discrete-time proportional-integral-derivative (PID) control on a single unit Kresling robot via a series of static set points to 17 mm, dynamic set point stepping, and sinusoidal signal following, with error under 3 mm up to 10 mm contraction. We also demonstrate a two-unit Kresling robot with two degree of freedom extension and rotation control, which has error of 1.7 mm and 6.1°. This work contributes optimized capacitive electrode design and the demonstration of closed-loop feedback position control without visual tracking as an input. This approach to capacitance sensing and modeling constitutes a major step towards proprioceptive state estimation and feedback control in soft origami robotics.

Modular multi-degree-of-freedom soft origami robots with reprogrammable electrothermal actuation

Soft robots often draw inspiration from nature to navigate different environments. Although the inching motion and crawling motion of caterpillars have been widely studied in the design of soft robots, the steering motion with local bending control remains challenging. To address this challenge, we explore modular origami units which constitute building blocks for mimicking the segmented caterpillar body. Based on this concept, we report a modular soft Kresling origami crawling robot enabled by electrothermal actuation. A compact and lightweight Kresling structure is designed, fabricated, and characterized with integrated thermal bimorph actuators consisting of liquid crystal elastomer and polyimide layers. With the modular design and reprogrammable actuation, a multiunit caterpillar-inspired soft robot composed of both active units and passive units is developed for bidirectional locomotion and steering locomotion with precise curvature control. We demonstrate the modular design of the Kresling origami robot with an active robotic module picking up cargo and assembling with another robotic module to achieve a steering function. The concept of modular soft robots can provide insight into future soft robots that can grow, repair, and enhance functionality.

Integrated Actuation and Sensing: Toward Intelligent Soft Robots

Soft robotics has received substantial attention due to its remarkable deformability, making it well-suited for a wide range of applications in complex environments, such as medicine, rescue operations, and exploration. Within this domain, the interaction of actuation and sensing is of utmost importance for controlling the movements and functions of soft robots. Nonetheless, current research predominantly focuses on isolated actuation and sensing capabilities, often neglecting the critical integration of these 2 domains to achieve intelligent functionality. In this review, we present a comprehensive survey of fundamental actuation strategies and multimodal actuation while also delving into advancements in proprioceptive and haptic sensing and their fusion. We emphasize the importance of integrating actuation and sensing in soft robotics, presenting 3 integration methodologies, namely, sensor surface integration, sensor internal integration, and closed-loop system integration based on sensor feedback. Furthermore, we highlight the challenges in the field and suggest compelling directions for future research. Through this comprehensive synthesis, we aim to stimulate further curiosity among researchers and contribute to the development of genuinely intelligent soft robots.

Origami Polyhedra-Based Soft Multicellular Robots

The reconfigurable and modular method, and the adaptive morphology method are two main methodologies to achieve the multimodal robots. Basically, the former method mimics the biological multicellular systems, while the latter is mostly inspired by the multimodal animals. Herein inspired by the rhombic dodecahedron (RDD) origami model, a novel type of soft multicellular robots with multimodal locomotion is presented. Morphologically, the combinable and expandable three-dimensional (3D)-printed soft RDD cells are assembled into several typical patterns: in-line, cross shaped, oblong shaped, and parallelogra shaped. The kinematics based on the sequential monolithic deformations of soft RDDs is analyzed to generate multimodal locomotion: peristaltic crawling, two-anchor crawling, crawling with turning functions, and omnidirectional crawling through the propagating waves in two orthogonal directions. More encouragingly, without reorganizing the pattern or reshaping the morph, the in-line multicellular robots manifest excellent climbing abilities, where the built-in rhombic meshes alternately tighten and loosen the pole-like structures to provide the gripping forces reliably without sacrificing mobility. To wrap up, owing to the monolithic and hierarchical deformability, high reconfigurability, and 3D-printable manufacturability of the RDD, we anticipate that the soft multicellular robot can potentially manifest further contributions to the advanced robotics with embodied intelligence, such as task-oriented self-assembly robots, self-reconfigurable robotic systems, and goal-directed metamorphosis robots.

Bioinspired Soft Electrostatic Accordion-Fold Actuators

Increasing interests have been directed toward the exploitation of origami techniques in developing biomimetic soft robots. There is a need for effective design solutions to exploit the properties of origami structure with simplified assembly and improved robotic mobility. In this study, inspired by human long-standing jumps, we present a soft electrostatically driven legged accordion fold actuator made by turning a flat paper into hollow polyhedron structure with a spring like rear and capable of electrostatic pad-assisted steering and carrying loads. Without the need for integration of external actuators, the actuator is composed of the electrostatic origami actuator itself supported by a single-fold leg with fast response, easy fabrication process, and low cost. Initiated by periodic deformation around the folding hinges caused by alternating current voltage and ground reaction forces, the actuators exhibit a unique jump-slide movement outperforming other existing soft electrostatic actuators/robots in terms of relative speed. We examined the effect of different geometric and external factors on the relative speed and highlighted the significance of body scale and short-edge panels as the elastic elements, as well as operating at resonance frequency in producing effective performances. Theoretical locomotion models and finite element analysis were carried out to interpret the working principle and validate experimental results.

Bioinspired 3D flexible devices and functional systems

Flexible devices and functional systems with elaborated three-dimensional (3D) architectures can endow better mechanical/electrical performances, more design freedom, and unique functionalities, when compared to their two-dimensional (2D) counterparts. Such 3D flexible devices/systems are rapidly evolving in three primary directions, including the miniaturization, the increasingly merged physical/artificial intelligence and the enhanced adaptability and capabilities of heterogeneous integration. Intractable challenges exist in this emerging research area, such as relatively poor controllability in the locomotion of soft robotic systems, mismatch of bioelectronic interfaces, and signal coupling in multi-parameter sensing. By virtue of long-time-optimized materials, structures and processes, natural organisms provide rich sources of inspiration to address these challenges, enabling the design and manufacture of many bioinspired 3D flexible devices/systems. In this Review, we focus on bioinspired 3D flexible devices and functional systems, and summarize their representative design concepts, manufacturing methods, principles of structure-function relationship and broad-ranging applications. Discussions on existing challenges, potential solutions and future opportunities are also provided to usher in further research efforts toward realizing bioinspired 3D flexible devices/systems with precisely programmed shapes, enhanced mechanical/electrical performances, and high-level physical/artificial intelligence.

Active Materials for Functional Origami

In recent decades, origami has been explored to aid in the design of engineering structures. These structures span multiple scales and have been demonstrated to be used toward various areas such as aerospace, metamaterial, biomedical, robotics, and architectural applications. Conventionally, origami or deployable structures have been actuated by hands, motors, or pneumatic actuators, which can result in heavy or bulky structures. On the other hand, active materials, which reconfigure in response to external stimulus, eliminate the need for external mechanical loads and bulky actuation systems. Thus, in recent years, active materials incorporated with deployable structures have shown promise for remote actuation of light weight, programmable origami. In this review, active materials such as shape memory polymers (SMPs) and alloys (SMAs), hydrogels, liquid crystal elastomers (LCEs), magnetic soft materials (MSMs), and covalent adaptable network (CAN) polymers, their actuation mechanisms, as well as how they have been utilized for active origami and where these structures are applicable is discussed. Additionally, the state-of-the-art fabrication methods to construct active origami are highlighted. The existing structural modeling strategies for origami, the constitutive models used to describe active materials, and the largest challenges and future directions for active origami research are summarized.

Variable Stiffness Fibers Enabled Universal and Programmable Re-Foldability Strategy for Modular Soft Robotics

Origami is a rich source of inspiration for creating soft actuators with complex deformations. However, implementing the re-foldability of origami on soft actuators remains a significant challenge. Herein, a universal and programmable re-foldability strategy is reported to integrate multiple origami patterns into a single soft origami actuator, thereby enabling multimode morphing capability. This strategy can selectively activate and deactivate origami creases through variable stiffness fibers. The utilization of these fibers enables the programmability of crease pattern quantity and types within a single actuator, which expands the morphing modes and deformation ranges without increasing their physical size and chamber number. The universality of this approach is demonstrated by developing a series of re-foldable soft origami actuators. Moreover, these soft origami actuators are utilized to construct a bidirectional crawling robot and a multimode soft gripper capable of adapting to object size, grasping orientation, and placing orientation. This work represents a significant step forward in the design of multifunctional soft actuators and holds great potential for the advancement of agile and versatile soft robots.

Constrained Origami Artificial Muscle-Driven Robotic Manipulator Capable of Coordinating Twisting and Grasping Motions for Object Manipulation

Grasping and twisting motions are vital when manipulating objects due to their fundamental role in enabling precision, adaptability, and effective interaction. However, few studies in soft robotics exploiting artificial muscles have achieved object manipulation in situ through the coordination of twisting and grasping motions akin to our forearm and hand's capabilities. Especially, when using the same artificial muscle module to achieve these two motions will greatly simplify the manufacturing and control complexity. Here, we introduce identical origami artificial muscle modules (OAMMs) subjected to distinct end constraints into the design of the robotic manipulator, allowing it to achieve independent grasping and twisting motions to achieve effective, precise object manipulation. Applying different end constraints to the identical OAMMs yields distinct motions at their ends, where utilizing a fixed end and a sliding end realizes pure translation, while opting for a fixed end and a rotating end enables pure rotation. The differentially constrained OAMMs then serve as soft actuators for the manipulator's torsional mechanism and grasping mechanism to accomplish independent, controllable twisting and grasping motions. The coordination of twisting and grasping motions finally enables the manipulator to complete various tasks, including installing a light bubble, pouring the water from a lidded bottle into a cup, and sorting and stacking puzzle blocks. Our study pioneers the utilization of OAMMs for precise and versatile object manipulation through the coordination of independent twisting and grasping motions.

3D-Printed Origami Actuators for a Multianimal-Inspired Soft Robot with Amphibious Locomotion and Tongue Hunting

The field of soft robotics is rapidly evolving, and there is a growing interest in developing soft robots with bioinspired features for use in various applications. This research presented the design and development of 3D-printed origami actuators for a soft robot with amphibious locomotion and tongue hunting capabilities. Two different types of programmable origami actuators were designed and manufactured, namely Z-shaped and twist tower actuators. In addition, two actuator variations were developed based on the Z-shaped actuator, including the pelvic fin and the coiling/uncoiling types. The Z-shaped actuators were used for the rear legs to facilitate the locomotion of the water-like frogs. Meanwhile, the twisted tower actuators were used for the rotation joints in the forelegs and for locomotion on land. The pelvic fin actuator was developed to imitate the land locomotion of the mudskipper, and the coiling/uncoiling actuator was designed for tongue hunting motion. The origami actuators and soft robot prototype were tested through a series of experiments, which showed that the robot was capable of efficiently moving in water and on land and performing tongue hunting motions. Our results demonstrate the effectiveness of these actuators in producing the desired motions and provide insights into the potential of applying 3D-printed origami actuators in the development of soft robots with bioinspired features.

Self-Locking Pneumatic Actuators Formed from Origami Shape-Morphing Sheets

The art of origami has gained traction in various fields such as architecture, the aerospace industry, and soft robotics, owing to the exceptional versatility of flat sheets to exhibit complex shape transformations. Despite the promise that origami robots hold, their use in high-capacity environments has been limited due to the lack of rigidity. This article introduces novel, origami-inspired, self-locking pneumatic modular actuators (SPMAs), enabling them to operate in such environments. Our innovative approach is based on origami patterns that allow for various types of shape morphing, including linear and rotational motion. We have significantly enhanced the stiffness of the actuators by embedding magnets in composite sheets, thus facilitating their application in real-world scenarios. In addition, the embedded self-adjustable valves facilitate the control of sequential origami actuations, making it possible to simplify the pneumatic system for actuating multimodules. With just one actuation source and one solenoid valve, the valves enable efficient control of our SPMAs. The SPMAs can control robotic arms operating in confined spaces, and the entire system can be modularized to accomplish various tasks. Our results demonstrate the potential of origami-inspired designs to achieve more efficient and reliable robotic systems, thus opening up new avenues for the development of robotic systems for various applications.

Inverse Origami Design Model for Soft Robotic Development

Origami provides an opportunity to construct a wide range of 3D functional structures by folding a flat sheet. It can be used to develop various soft functional robots by combining soft smart actuators. However, a simple and an effective model that can address the challenging problem of designing origami patterns to connect origami design with robotics is lacking, thereby greatly increasing the threshold of soft origami robots and hindering its development. This study proposes an easy-to-use inverse origami design model to generate the flat crease pattern from the desired folded shape automatically while simulating origami morphing by simply providing the shape parameters or 2D shape graphics. This method overcomes the difficulty of origami design and enables a close connection between origami and robotics. Through this method, various soft origami robots can be developed with low design complexity and time cost to achieve different functions, thereby promoting the development of soft origami robots.

A magnetic multi-layer soft robot for on-demand targeted adhesion

Magnetic soft robots have shown great potential for biomedical applications due to their high shape reconfigurability, motion agility, and multi-functionality in physiological environments. Magnetic soft robots with multi-layer structures can enhance the loading capacity and function complexity for targeted delivery. However, the interactions between soft entities have yet to be fully investigated, and thus the assembly of magnetic soft robots with on-demand motion modes from multiple film-like layers is still challenging. Herein, we model and tailor the magnetic interaction between soft film-like layers with distinct in-plane structures, and then realize multi-layer soft robots that are capable of performing agile motions and targeted adhesion. Each layer of the robot consists of a soft magnetic substrate and an adhesive film. The mechanical properties and adhesion performance of the adhesive films are systematically characterized. The robot is capable of performing two locomotion modes, i.e., translational motion and tumbling motion, and also the on-demand separation with one side layer adhered to tissues. Simulation results are presented, which have a good qualitative agreement with the experimental results. The feasibility of using the robot to perform multi-target adhesion in a stomach is validated in both ex-vivo and in-vivo experiments.

Rigid-foldable cylindrical origami with tunable mechanical behaviors

Rigid-foldable origami shows significant promise in advanced engineering applications including deployable structures, aerospace engineering, and robotics. It undergoes deformation solely at the creases during the folding process while maintaining rigidity throughout all facets. However, most types of cylindrical origami, such as Kresling origami, water-bomb origami, and twisted tower origami, lack rigid-foldability. Although shape transformation can be achieved through elastic folding, their limited rigid foldability constrains their engineering applications. To address this limitation, we proposed a type of cylindrical origami inspired by Kresling origami, named foldable prism origami (FP-ori), in this paper. FP-ori possesses not only rigid-foldability but also several tunable properties, including flat-foldability, self-locking, and bistability. The geometric properties of FP-ori were analyzed and the relationship between different parameters and tunable mechanical behaviors were verified through finite element method simulations, as well as experiments using paper models. Furthermore, we proposed stacked structures composed of multiple cubic FP-ori units, the rotation directions of which could be controlled through the combination arrangement. And drawing inspiration from kirigami, a negative Poisson's ratio tessellation structure was created. These results indicated that FP-ori has substantial potential for broad application in engineering fields.

Digital Mechanical Metamaterial: Encoding Mechanical Information with Graphical Stiffness Pattern for Adaptive Soft Machines

Inspired by the adaptive features exhibited by biological organisms like the octopus, soft machines that can tune their shape and mechanical properties have shown great potential in applications involving unstructured and continuously changing environments. However, current soft machines are far from achieving the same level of adaptability as their biological counterparts, hampered by limited real-time tunability and severely deficient reprogrammable space of properties and functionalities. As a steppingstone toward fully adaptive soft robots and smart interactive machines, an encodable multifunctional material that uses graphical stiffness patterns is introduced here to in situ program versatile mechanical capabilities without requiring additional infrastructure. Through independently switching the digital binary stiffness states (soft or rigid) of individual constituent units of a simple auxetic structure with elliptical voids, in situ and gradational tunability is demonstrated here in various mechanical qualities such as shape-shifting and -memory, stress-strain response, and Poisson's ratio under compressive load as well as application-oriented functionalities such as tunable and reusable energy absorption and pressure delivery. This digitally programmable material is expected to pave the way toward multienvironment soft robots and interactive machines.

Bio-Inspired Untethered Robot-Sensor Platform for Minimally Invasive Biomedical Sensing

Conventional catheter- or probe-based in vivo biomedical sensing is uncomfortable, inconvenient, and sometimes infeasible for long-term monitoring. Existing implantable sensors often require an invasive procedure for sensor placement. Untethered soft robots with the capability to deliver the sensor to the desired monitoring point hold great promise for minimally invasive biomedical sensing. Inspired by the locomotion modes of snakes, we present here a soft kirigami robot for sensor deployment and real-time wireless sensing. The locomotion mechanism of the soft robot is achieved by kirigami patterns that offer asymmetric tribological properties that mimic the skin of the snake. The robot exhibits good deployability, excellent load capacity (up to 150 times its own weight), high-speed locomotion (0.25 body length per step), and wide environmental adaptability with multimodal movements (obstacle crossing, locomotion in wet and dry conditions, climbing, and inverted crawling). When integrated with passive sensors, the versatile soft robot can locomote inside the human body, deliver the passive sensor to the desired location, and hold the sensor in place for real-time monitoring in a minimally invasive manner. The proof-of-concept prototype demonstrates that the platform can perform real-time impedance monitoring for the diagnosis of gastroesophageal reflux disease.

A Design Method for Rectangular Waveguide-Typed Microwave Devices Based on a Novel Origami Process

A novel design method based on a novel origami process that can create a solid structure swiftly and at a low cost is presented for rectangular waveguide-type microwave devices in this paper. A planar structure was fabricated by the lamination and laser cutting of polystyrene membranes and aluminum foils and was converted into a solid structure via origami in accordance with the selective absorption of infrared light. A rectangular waveguide, a rectangular waveguide-type coupler, and a power divider based on an origami structure with a multi-layer structure and a single-layer structure were fabricated and tested, demonstrating easy assembly and good microwave performance. The measured results of the rectangular waveguide indicated that the insertion loss was superior to -0.9 dB. Meanwhile, the results of the coupler showed that the coupling degree increased from -12.8 dB to -8.9 dB in the range of 11.0 GHz to 12.0 GHz. Correspondingly, the prepared power divider demonstrated that the return loss dwindled from -8.9 dB to -11.3 dB and that the insertion loss of one output port was approximate to that of the remaining one, varying between -3.5 dB and -5.2 dB in the range of 10.5 GHz to 11.5 GHz-verifying the effectiveness of the origami-based design method.

Cellular Automata Inspired Multistable Origami Metamaterials for Mechanical Learning

Recent advances in multistable metamaterials reveal a link between structural configuration transition and Boolean logic, heralding a new generation of computationally capable intelligent materials. To enable higher-level computation, existing computational frameworks require the integration of large-scale networked logic gates, which places demanding requirements on the fabrication of materials counterparts and the propagation of signals. Inspired by cellular automata, a novel computational framework based on multistable origami metamaterials by incorporating reservoir computing is proposed, which can accomplish high-level computation tasks without the need to construct a logic gate network. This approach thus eliminates the demanding requirements for the fabrication of materials and signal propagation when constructing large-scale networks for high-level computation in conventional mechanical logic. Using the multistable stacked Miura-origami metamaterial as a validation platform, digit recognition is experimentally implemented by a single actuator. Moreover, complex tasks, such as handwriting recognition and 5-bit memory tasks, are also shown to be feasible with the new computation framework. The research represents a significant advancement in developing a new generation of intelligent materials with advanced computational capabilities. With continued research and development, these materials can have a transformative impact on a wide range of fields, from computational science to material mechano-intelligence technology and beyond.

Embodying Multifunctional Mechano-Intelligence in and Through Phononic Metastructures Harnessing Physical Reservoir Computing

Recent advances in autonomous systems have prompted a strong demand for the next generation of adaptive structures and materials to possess built-in intelligence in their mechanical domain, the so-called mechano-intelligence (MI). Previous MI attempts mainly focused on specific case studies and lacked a systematic foundation in effectively and efficiently constructing and integrating different intelligent functions. Here, a new approach is uncovered to create multifunctional MI in adaptive structures using physical reservoir computing (PRC). That is, to concurrently embody computing power and the key elements of intelligence, namely perception, decision-making, and commanding, directly in the mechanical domain, advancing from conventional reliance on add-on computers and massive electronics. As an exemplar platform, a mechanically intelligent phononic metastructure is developed by harnessing its high-degree-of-freedom nonlinear dynamics as PRC power. Through analyses and experiments, multiple intelligent structural functions are demonstrated ranging from self-tuning wave controls to wave-based logic gates. This research provides the much-needed basis for creating future smart structures and materials that greatly surpass the state of the art-such as lower power consumption, more direct interactions, and better survivability in harsh environments or under cyberattacks. Moreover, it enables the addition of new functions and autonomy to systems without overburdening the onboard computers.

Muscle-inspired soft robots based on bilateral dielectric elastomer actuators

Muscle groups perform their functions in the human body via bilateral muscle actuation, which brings bionic inspiration to artificial robot design. Building soft robotic systems with artificial muscles and multiple control dimensions could be an effective means to develop highly controllable soft robots. Here, we report a bilateral actuator with a bilateral deformation function similar to that of a muscle group that can be used for soft robots. To construct this bilateral actuator, a low-cost VHB 4910 dielectric elastomer was selected as the artificial muscle, and polymer films manufactured with specific shapes served as the actuator frame. By end-to-end connecting these bilateral actuators, a gear-shaped 3D soft robot with diverse motion capabilities could be developed, benefiting from adjustable actuation combinations. Lying on the ground with all feet on the ground, a crawling soft robot with dexterous movement along multiple directions was realized. Moreover, the directional steering was instantaneous and efficient. With two feet standing on the ground, it also acted as a rolling soft robot that can achieve bidirectional rolling motion and climbing motion on a 2° slope. Finally, inspired by the orbicularis oris muscle in the mouth, a mouthlike soft robot that could bite and grab objects 5.3 times of its body weight was demonstrated. The bidirectional function of a single actuator and the various combination modes among multiple actuators together allow the soft robots to exhibit diverse functionalities and flexibility, which provides a very valuable reference for the design of highly controllable soft robots.

Multi-Stability of the Extensible Origami Structures

Multi-stable structures and metamaterials with more than two stable states are widely applied in diversified engineering applications. Non-rigid foldable origami patterns have provided an effective way of designing multi-stable structures. But most of them have only two stable states and therefore require a combination of many units to achieve multi-stability. Here, a series of extensible origami structures are proposed with generic multi-stability based on non-rigid wrapping origami. Through a kinematic analysis and experiments, it is demonstrate that a sequential folding among different layers of the structures is created to generate a continuous rigid origami range and several discrete rigid origami states, which consequently leads to the multi-stability of the extensible origami structures. Moreover, the effects of design parameters on the mechanical properties of the structures are investigated by numerical simulation, enabling properties programmability upon specific needs. This study thus paves a new pathway for the development of novel multi-stable origami structures.

Kirigami Makes a Soft Magnetic Sheet Crawl

Limbless crawling on land requires breaking symmetry of the friction with the ground and exploiting an actuation mechanism to generate propulsive forces. Here, kirigami cuts are introduced into a soft magnetic sheet that allow to achieve effective crawling of untethered soft robots upon application of a rotating magnetic field. Bidirectional locomotion is achieved under clockwise and counterclockwise rotating magnetic fields with distinct locomotion patterns and crawling speed in forward and backward propulsions. The crawling and deformation profiles of the robot are experimentally characterized and combined with detailed multiphysics numerical simulations to extract locomotion mechanisms in both directions. It is shown that by changing the shape of the cuts and orientation of the magnet the robot can be steered, and if combined with translational motion of the magnet, complex crawling paths are programed. The proposed magnetic kirigami robot offers a simple approach to developing untethered soft robots with programmable motion.

Photocontrollable Elongation Actuation of Liquid Crystal Elastomer Films with Well-Defined Crease Structures

Although liquid crystal elastomers (LCEs) have demonstrated various applications in artificial muscles and soft robotics, their inherent flexibility and orientation-dependent forces limit their functions. For instance, LCEs can sustain a high actuation force when they contract but cannot elongate to drive loads with large displacements. In this study, it is demonstrated that photocontrollable elongation actuation with a large strain can be achieved in polydomain LCEs by programming the crease structures in a well-defined order to couple the actuation forces. Efficient photoactuation without overheating-induced damage to the materials is favored, based on the well-designed photosensitive molecular switch crosslinker via the synergy of photochemical and photothermal effects. The LCE actuator can jack up heavy loads, elongate freely, and contract back to manipulate distant objects. Theoretical analysis based on a finite element simulation of the deformation energy during the actuation process reveals a trade-off between the abilities of jacking-up and withstanding load. More importantly, this study simplifies the design of a single material with functions inherent only in other soft robotic devices based on the assembly of multiple modules, thus providing a design strategy for surpassing instinctive properties of conventional soft materials to expand the functions of soft robotics.

Omnidirectional compliance on cross-linked actuator coordination enables simultaneous multi-functions of soft modular robots

Earthworms have entirely soft bodies mainly composed of circular and longitudinal muscle bundles but can handle the complexity of unstructured environments with exceptional multifunctionality. Soft robots are naturally appropriate for mimicking soft animal structures thanks to their inherent compliance. Here, we explore the new possibility of using this compliance to coordinate the actuation movements of single-type soft actuators for not only high adaptability but the simultaneous multifunctionality of soft robots. A cross-linked actuator coordination mechanism is proposed and explained with a novel conceptual design of a cross-linked network, characterization of modular coordinated kinematics, and a modular control strategy for multiple functions. We model and analyze the motion patterns for these functions, including grabbing, manipulation, and locomotion. This further enables the combination of simultaneous multi-functions with this very simple actuator network structure. In this way, a soft modular robot is developed with demonstrations of a novel continuous-transportation mode, for which multiple objects could be simultaneously transported in unstructured environments with either mobile manipulation or pick-and-place operation. A comprehensive workflow is presented to elaborate the cross-linked actuator coordination concept, analytical modeling, modular control strategy, experimental validation, and multi-functional applications. Our understanding of actuator coordination inspires new soft robotic designs for wider robotic applications.

A Magnetic Bio-Inspired Soft Carrier as a Temperature-Controlled Gastrointestinal Drug Delivery System

Currently, gastrointestinal bleeding in the colon wall and the small bowel is diagnosed and treated with endoscopes. However, the locations of this condition are often problematic to treat using traditional flexible and tethered tools. New studies commonly consider untethered devices for solving this problem. However, there still exists a gap in the extant literature, and more research is needed to diagnose and deliver drugs in the lower gastrointestinal tract using soft robotic carriers. This paper discusses the development of an untethered, magnetically-responsive bio-inspired soft carrier. A molding process is utilized to produce prototypes from Diisopropylidene-1,6-diphenyl-1,6-hexanediol-based Polymer with Ethylene Glycol Dimethacrylate (DiAPLEX) MP-3510 - a shape memory polymer with a low transition temperature to enable the fabrication of these carriers. The soft carrier design is validated through simulation results of deformation caused by magnetic elements embedded in the carrier in response to an external field. The thermal responsiveness of the fabricated prototype carriers is assessed ex vivo and in a phantom. The results indicate a feasible design capable of administering drugs to a target inside a phantom of a large intestine. The soft carrier introduces a method for the controlled release of drugs by utilizing the rubbery modulus of the polymer and increasing the recovery force through magnetic actuation.

Untethered shape-changing devices in the gastrointestinal tract

INTRODUCTION

Advances in microfabrication, automation, and computer engineering seek to revolutionize small-scale devices and machines. Emerging trends in medicine point to smart devices that emulate the motility, biosensing abilities, and intelligence of cells and pathogens that inhabit the human body. Two important characteristics of smart medical devices are the capability to be deployed in small conduits, which necessitates being untethered, and the capacity to perform mechanized functions, which requires autonomous shape-changing.

AREAS COVERED

We motivate the need for untethered shape-changing devices in the gastrointestinal tract for drug delivery, diagnosis, and targeted treatment. We survey existing structures and devices designed and utilized across length scales from the macro to the sub-millimeter. These devices range from triggerable pre-stressed thin film microgrippers and spring-loaded devices to shape-memory and differentially swelling structures.

EXPERT OPINION

Recent studies demonstrate that when fully enabled, tether-free and shape-changing devices, especially at sub-mm scales, could significantly advance the diagnosis and treatment of GI diseases ranging from cancer and inflammatory bowel disease (IBD) to irritable bowel syndrome (IBS) by improving treatment efficacy, reducing costs, and increasing medication compliance. We discuss the challenges and possibilities associated with ensuring safe, reliable, and autonomous operation of these smart devices.

Triggering Magnets for Wiegand Sensors: Electrodeposited and Origami-Magnetized CoNiP Micro-Magnets

Miniature sensors are key components for applications in the Internet of Things (IoT), wireless sensor networks, autonomous vehicles, smart cities, and smart manufacturing. As a miniature and self-powered magnetic sensor, the Wiegand sensor possesses advantageous traits including changing-rate-independent output, low cost, and remarkable repeatability and reliability. A typical Wiegand sensor requires hard magnetic pole pieces that provide external fields for triggering voltage outputs that are called Wiegand pulses. However, the wire-shaped sensing element of Wiegand sensors is the critical issue that limits the design, selection, and adoption of the external triggering magnets. Currently, the widely used pole piece materials are rare-earth magnets. However, adopting rare-earth magnets brings strong stray fields, causing an electromagnetic interference (EMI) problem. In this study, patterned CoNiP hard magnets were electrodeposited on flexible substrates through microfabrication. Origami magnetization was utilized to control the resultant stray fields and thus the pole piece of CoNiP magnets can successfully trigger the output of the Wiegand pulse. In comparison, the output voltage of the triggered pulse acquired through the patterned CoNiP magnets is comparable to that acquired by using the rare-earth magnets. Furthermore, both the volume (and hence the weight) of the Wiegand sensor and the EMI issue can be significantly reduced and mitigated, respectively, by the CoNiP magnets.

Robotic Materials Transformable Between Elasticity and Plasticity

Robotic materials, with coupled sensing, actuation, computation, and communication, have attracted increasing attention because they are able to not only tune their conventional passive mechanical property via geometrical transformation or material phase change but also become adaptive and even intelligent to suit varying environments. However, the mechanical behavior of most robotic materials is either reversible (elastic) or irreversible (plastic), but not transformable between them. Here, a robotic material whose behavior is transformable between elastic and plastic is developed, based upon an extended neutrally stable tensegrity structure. The transformation does not depend on conventional phase transition and is fast. By integrating with sensors, the elasticity-plasticity transformable (EPT) material is able to self-sense deformation and decides whether to undergo transformation or not. This work expands the capability of the mechanical property modulation of robotic materials.

3D Chiral Micro-Pinwheels Based on Rolling-Up Kirigami Technology

Expanding micro-/nanostructures into 3D ones results not only in boosting structural integration level with compact geometry but also enhancing a device's complexity and functionality. Herein, a synergetic 3D micro-/nanoshape transformation is proposed by combining kirigami and rolling-up techniques, or rolling-up kirigami, for the first time. As an example, micro-pinwheels with multiple flabella are patterned on pre-stressed bilayer membranes and rolled up into 3D structures. The flabella are designed when they are patterned on a 2D thin film, facilitating the integration of micro-/nanoelement and other functionalization processes during 2D patterning, which is typically much easier than post-shaping an as-fabricated 3D structure by removing redundant materials or 3D printing. The dynamic rolling-up process is simulated using elastic mechanics with a movable releasing boundary. Mutual competition and cooperation among flabella are observed during the whole release process. More importantly, the mutual conversion between translation and rotation offers a reliable platform for developing parallel microrobots and adaptive 3D micro-antennas. Additionally, 3D chiral micro-pinwheel arrays integrated into a microfluidic chip are successfully applied to detect organic molecules in solution using a terahertz apparatus. With an extra actuation, active micro-pinwheels can potentially serve as a base to functionalize 3D kirigami as tunable devices.

One-Pot Synthesis of Depolymerizable δ-Lactone Based Vitrimers

A depolymerizable vitrimer that allows both reprocessability and monomer recovery by a simple and scalable one-pot two-step synthesis of vitrimers from cyclic lactones is reported. Biobased δ-valerolactone with alkyl substituents (δ-lactone) has low ceiling temperature; thus, their ring-opening-polymerized aliphatic polyesters are capable of depolymerizing back to monomers. In this work, the amorphous poly(δ-lactone) is solidified into an elastomer (i.e., δ-lactone vitrimer) by a vinyl ether cross-linker with dynamic acetal linkages, giving the merits of reprocessing and healing. Thermolysis of the bulk δ-lactone vitrimer at 200 °C can recover 85-90 wt% of the material, allowing reuse without losing value and achieving a successful closed-loop life cycle. It further demonstrates that the new vitrimer has excellent properties, with the potential to serve as a biobased and sustainable replacement of conventional soft elastomers for various applications such as lenses, mold materials, soft robots, and microfluidic devices.

Soft and lightweight fabric enables powerful and high-range pneumatic actuation

Soft structures and actuation allow robots, conventionally consisting of rigid components, to perform more compliant, adaptive interactions similar to living creatures. Although numerous functions of these types of actuators have been demonstrated in the literature, their hyperelastic designs generally suffer from limited workspaces and load-carrying capabilities primarily due to their structural stretchability factor. Here, we describe a series of pneumatic actuators based on soft but less stretchable fabric that can simultaneously perform tunable workspace and bear a high payload. The motion mode of the actuator is programmable, combinable, and predictable and is informed by rapid response to low input pressure. A robotic gripper using three fabric actuators is also presented. The gripper demonstrates a grasping force of over 150 N and a grasping range from 70 to 350 millimeters. The design concept and comprehensive guidelines presented would provide design and analysis foundations for applying less stretchable yet soft materials in soft robots to further enhance their practicality.

A Torsion-Bending Antagonistic Bistable Actuator Enables Untethered Crawling and Swimming of Miniature Robots

Miniature robots show great potential in exploring narrow and confined spaces to perform various tasks, but many applications are limited by the dependence of these robots on electrical or pneumatic tethers to power supplies outboard. Developing an onboard actuator that is small in size and powerful enough to carry all the components onboard is a major challenge to eliminate the need for a tether. Bistability can trigger a dramatic energy release during switching between the 2 stable states, thus providing a promising way to overcome the intrinsic limitation of insufficient power of small actuators. In this work, the antagonistic action between torsional deflection and bending deflection in a lamina emergent torsional joint is utilized to achieve bistability, yielding a buckling-free bistable design. The unique configuration of this bistable design enables integrating of a single bending electroactive artificial muscle in the structure to form a compact, self-switching bistable actuator. A low-voltage ionic polymer-metal composites artificial muscle is employed, yielding a bistable actuator capable of generating an instantaneous angular velocity exceeding 300 °/s by a 3.75-V voltage. Two untethered robotic demonstrations using the bistable actuator are presented, including a crawling robot (gross weight of 2.7 g, including actuator, battery, and on-board circuit) that can generate a maximum instantaneous velocity of 40 mm/s and a swimming robot equipped with a pair of origami-inspired paddles that swims breaststroke. The low-voltage bistable actuator shows potential for achieving autonomous motion of various fully untethered miniature robots.

Oribron: An Origami-Inspired Deformable Rigid Bronchoscope for Radial Support

The structure of a traditional rigid bronchoscope includes proximal, distal, and body, representing an important means to treat hypoxic diseases. However, the body structure is too simple, resulting in the utilization rate of oxygen being usually low. In this work, we reported a deformable rigid bronchoscope (named Oribron) by adding a Waterbomb origami structure to the body. The Waterbomb's backbone is made of films, and the pneumatic actuators are placed inside it to achieve rapid deformation at low pressure. Experiments showed that Waterbomb has a unique deformation mechanism, which can transform from a small-diameter configuration (#1) to a large-diameter configuration (#2), showing excellent radial support capability. When Oribron entered or left the trachea, the Waterbomb remained in #1. When Oribron is working, the Waterbomb transforms from #1 to #2. Since #2 reduces the gap between the bronchoscope and the tracheal wall, it effectively slows down the rate of oxygen loss, thus promoting the absorption of oxygen by the patient. Therefore, we believe that this work will provide a new strategy for the integrated development of origami and medical devices.

Venation-Mimicking, Ultrastretchable, Room-Temperature-Attachable Metal Tapes for Integrated Electronic Skins

Future electronic skin systems require stretchable conductors and low-temperature integration of external components, which remains challenging for traditional metal films. Herein, a bioinspired design concept is reported to endow metal films with 200% stretchability as well as room-temperature integration capability with diverse components. It is revealed that by controllable implantation of defects, distinctive venation-mimicking cracking modes can be induced in strained metal films, leading to profound stretchability regulation. An intriguing exponential-to-linear transition of the film electromechanical performance is observed, which is elucidated by a unified model covering the essence of all modes. Combined with room-temperature integration capability, an integrated electronic skin is constructed with metal films serving as stretchable electrodes, diverse sensors, and "tapes" to attach subcomponents, showing prospects in helping disabled people. This one-step, defect implantation strategy is applicable to common metals without special substrate treatments, which enables fascinating ultrastretchable metal film conductors with low-temperature integration capability to spark more sophisticated flexible electronic systems.

Wireless Inchworm-like Compact Soft Robot by Induction Heating of Magnetic Composite

Microrobots and nanorobots have been produced with various nature-inspired soft materials and operating mechanisms. However, freely operating a wirelessly miniaturized soft robot remains a challenge. In this study, a wireless crawling compact soft robot using induction heating was developed. The magnetic composite heater built into the robot was heated wirelessly via induction heating, causing a phase change in the working fluid surrounding the heater. The pressure generated from the evaporated fluid induces the bending of the robot, which is composed of elastomers. During one cycle of bending by heating and shrinking by cooling, the difference in the frictional force between the two legs of the robot causes it to move forward. This robot moved 7240 μm, representing 103% of its body length, over nine repetitions. Because the robot's surface is made of biocompatible materials, it offers new possibilities for a soft exploratory microrobot that can be used inside a living body or in a narrow pipe.

Actuation and design innovations in earthworm-inspired soft robots: A review

Currently, soft robotics technologies are creating the means of robotic abilities and are required for the development of biomimetic robotics. In recent years, earthworm-inspired soft robot has garnered increasing attention as a major branch of bionic robots. The major studies on earthworm-inspired soft robots focuses on the deformation of the earthworm body segment. Consequently, various actuation methods have been proposed to conduct the expansion and contraction of the robot's segments for locomotion simulation. This review article aims to act as a reference guide for researchers interested in the field of earthworm-inspired soft robot, and to present the current state of research, summarize current design innovations, compare the advantages and disadvantages of different actuation methods with the purpose of inspiring future innovative orientations for researchers. Herein, earthworm-inspired soft robots are classified into single- and multi-segment types, and the characteristics of various actuation methods are introduced and compared according to the number of matching segments. Moreover, various promising application instances of the different actuation methods are detailed along with their main features. Finally, motion performances of the robots are compared by two normalized metrics-speed compared by body length and speed compared by body diameter, and future developments in this research direction are presented.

A soft microrobot with highly deformable 3D actuators for climbing and transitioning complex surfaces

The climbing microrobots have attracted growing attention due to their promising applications in exploration and monitoring of complex, unstructured environments. Soft climbing microrobots based on muscle-like actuators could offer excellent flexibility, adaptability, and mechanical robustness. Despite the remarkable progress in this area, the development of soft microrobots capable of climbing on flat/curved surfaces and transitioning between two different surfaces remains elusive, especially in open spaces. In this study, we address these challenges by developing voltage-driven soft small-scale actuators with customized 3D configurations and active stiffness adjusting. Combination of programmed strain distributions in liquid crystal elastomers (LCEs) and buckling-driven 3D assembly, guided by mechanics modeling, allows for voltage-driven, complex 3D-to-3D shape morphing (bending angle > 200°) at millimeter scales (from 1 to 10 mm), which is unachievable previously. These soft actuators enable development of morphable electroadhesive footpads that can conform to different curved surfaces and stiffness-variable smart joints that allow different locomotion gaits in a single microrobot. By integrating such morphable footpads and smart joints with a deformable body, we report a multigait, soft microrobot (length from 6 to 90 mm, and mass from 0.2 to 3 g) capable of climbing on surfaces with diverse shapes (e.g., flat plane, cylinder, wavy surface, wedge-shaped groove, and sphere) and transitioning between two distinct surfaces. We demonstrate that the microrobot could navigate from one surface to another, recording two corresponding ceilings when carrying an integrated microcamera. The developed soft microrobot can also flip over a barrier, survive extreme compression, and climb bamboo and leaf.

Dynamic morphological transformations in soft architected materials via buckling instability encoded heterogeneous magnetization

The geometric reconfigurations in three-dimensional morphable structures have a wide range of applications in flexible electronic devices and smart systems with unusual mechanical, acoustic, and thermal properties. However, achieving the highly controllable anisotropic transformation and dynamic regulation of architected materials crossing different scales remains challenging. Herein, we develop a magnetic regulation approach that provides an enabling technology to achieve the controllable transformation of morphable structures and unveil their dynamic modulation mechanism as well as potential applications. With buckling instability encoded heterogeneous magnetization profiles inside soft architected materials, spatially and temporally programmed magnetic inputs drive the formation of a variety of anisotropic morphological transformations and dynamic geometric reconfiguration. The introduction of magnetic stimulation could help to predetermine the buckling states of soft architected materials, and enable the formation of definite and controllable buckling states without prolonged magnetic stimulation input. The dynamic modulations can be exploited to build systems with switchable fluidic properties and are demonstrated to achieve capabilities of fluidic manipulation, selective particle trapping, sensitivity-enhanced biomedical analysis, and soft robotics. The work provides new insights to harness the programmable and dynamic morphological transformation of soft architected materials and promises benefits in microfluidics, programmable metamaterials, and biomedical applications.

Fabrication and Functionality Integration Technologies for Small-Scale Soft Robots

Small-scale soft robots are attracting increasing interest for visible and potential applications owing to their safety and tolerance resulting from their intrinsic soft bodies or compliant structures. However, it is not sufficient that the soft bodies merely provide support or system protection. More importantly, to meet the increasing demands of controllable operation and real-time feedback in unstructured/complicated scenarios, these robots are required to perform simplex and multimodal functionalities for sensing, communicating, and interacting with external environments during large or dynamic deformation with the risk of mismatch or delamination. Challenges are encountered during fabrication and integration, including the selection and fabrication of composite/materials and structures, integration of active/passive functional modules with robust interfaces, particularly with highly deformable soft/stretchable bodies. Here, methods and strategies of fabricating structural soft bodies and integrating them with functional modules for developing small-scale soft robots are investigated. Utilizing templating, 3D printing, transfer printing, and swelling, small-scale soft robots can be endowed with several perceptual capabilities corresponding to diverse stimulus, such as light, heat, magnetism, and force. The integration of sensing and functionalities effectively enhances the agility, adaptability, and universality of soft robots when applied in various fields, including smart manufacturing, medical surgery, biomimetics, and other interdisciplinary sciences.

Ingestible Functional Magnetic Robot with Localized Flexibility (MR-LF)

The integration of an ingestible dosage form with sensing, actuation, and drug delivery capabilities can enable a broad range of surgical-free diagnostic and treatment strategies. However, the gastrointestinal (GI) tract is a highly constrained and complex luminal construct that fundamentally limits the size of an ingestible system. Recent advancements in mesoscale magnetic crawlers have demonstrated the ability to effectively traverse complex and confined systems by leveraging magnetic fields to induce contraction and bending-based locomotion. However, the integration of functional components (e.g., electronics) in the proposed ingestible system remains fundamentally challenging. Herein, the creation of a centralized compartment in a magnetic robot by imparting localized flexibility (MR-LF) is demonstrated. The centralized compartment enables MR-LF to be readily integrated with modular functional components and payloads, such as commercial off-the-shelf electronics and medication, while preserving its bidirectionality in an ingestible form factor. The ability of MR-LF to incorporate electronics, perform drug delivery, guide continuum devices such as catheters, and navigate air-water environments in confined lumens is demonstrated. The MR-LF enables functional integration to create a highly-integrated ingestible system that can ultimately address a broad range of unmet clinical needs.

Kirigami-Inspired Programmable Soft Magnetoresponsive Actuators with Versatile Morphing Modes

Untethered soft magnetoresponsive actuators (SMRAs), which can realize rapid shape transformation, have attracted widespread attention for their strategic applications in exploration, transportation, and minimally invasive medicine. It remains a challenge to fabricate SMRAs with complicated morphing modes (more than bending and folding), limiting their applications to simple shape-morphing and locomotion. Herein, a method integrating the ancient kirigami art and an advanced mechanical assembly method is proposed, which realizes 2D-to-3D and 3D-to-3D complicated shape-morphing and precise magnetization programming through cut-guided deformation. The kirigami-inspired SMRAs exhibit good robustness after actuating more than 10000 times. An integrated finite element analysis method is developed to quantitatively predict the shape transformation of SMRAs under magnetic actuation. By leveraging this method, a set of 3D curved responsive morphologies with programmed Gaussian curvature are fabricated (e.g., ellipsoid and saddle structures), specifically 3D multilayer structures and face-like shapes with different expressions, which are difficult to realize using previous approaches. Furthermore, a bionic-scaled soft crawling robot with significant obstacle surmounting ability is fabricated using the kirigami-inspired method. The ability of the method to achieve programmable SMRAs with versatile morphing modes may broaden its applications in soft robotics, color-switchable devices, and clinical treatments.