Self-contained soft electrofluidic actuators

A Versatile Dual-Responsive Shape-Memory Gripper via Additive Manufacturing Toward High-Performance Cross-Scale Objects Maneuvering

Smart grippers serving as soft robotics have garnered extensive attentions owing to their great potentials in medical, biomedical, and industrial fields. Though a diversity of grippers that account for manipulating the small objects (e.g., tiny micrometer-scale droplets) or the big ones (e.g., centimeter-scale screw) has been proposed, however, cross-scale maneuvering of these two species leveraging an all-in-one intelligent gripper is still challenging. Here, a magnet/light dual-responsive shape-memory gripper (DR-SMG) is reported, based on the hybrid of Fe-nanoparticles and shape-memory polymers. Thanks to its photothermal effect, the closed-state DR-SMG switches to the open state under the synergetic cooperation of near-infrared-ray (NIR) and a circinate magnetic field, referring to the temporary state. On the other hand, once the NIR is loaded, the temporary opened DR-SMG would reconfigure to its permanent closed state owing to shape-memory effect. Leveraging this principle, DR-SMG can grasp and release diverse cross-scale objects ranging from micrometers to centimeters including metals, glass balls, polymers, and small liquids. Significantly, this versatile DR-SMG is capable of spatially delivering multifunctional chemical droplets and conductive liquid metals, thereby enabling lab-on-chip and electrical switch applications. This work provides new insights into intelligent grippers and further advances the field of soft robotics.

Human camouflage and expression via soft mask from reprogrammable chemical fluid skin

Developing a wearable, active, dynamic face-changing mask for human camouflage and expression is a substantial challenge. Many organisms achieve camouflage and expression through skin deformation and color change. Inspired by this, we report a reprogrammable chemical fluid skin, which achieves deformation through fluids like the skin of a pufferfish and achieves color change function like the skin of a chameleon. Based on the skin, we design a soft mask that allows switching between at least eight human faces at a time. The soft mask is lightweight, thin, and fits the wearer's head. Its actuation is silent and safe, and can realize facial switching, including facial color and shape. By wearing the soft mask, robots can show facial changes and expression modulation, and humans can change their faces as needed. Our work enables the implementation of transforming a human into other humans in the real world to achieve camouflage and expression, which, to date, exists only in people's imagination.

Flexible electro-hydraulic power chips

Emerging soft systems, including soft robots or wearable devices, actuated by fluidic means facilitate a series of inherent benefits, including safe human-robot interactions, lower costs, and adaptability in geometry for manipulating delicate objects. However, existing fluidic soft systems are facing a critical barrier: how to get rid of traditional rigid, bulky, and redundant fluid power/control components as well as develop their own flexible, portable, and universal fluidic components for implementing fully flexible, multi-circuit, and untethered autonomous systems. Here, we introduce a strategy of flexible electro-hydraulic power chips that enables multi-circuit independent pumping and control of soft systems in simple, compact, and lightweight forms. These electro-hydraulic power chips could be arbitrarily programmed through "line-plane-body" combinations of electro-hydraulic power "diode" or "triode" modules with high output density of 10.77 kPa/g and 2.15 L/min/g, and freely fabricated into the desired shapes and functions via multi-material 3D printing technique. Demonstrations of multi-circuit mass transfer, five-finger selective cooling, bird's multiple actuation, jellyfish's fast swimming show electro-hydraulic power chips' portable, powerful, and multi-circuit independent attributes. The proposed strategy is an important advance towards low-cost, mass-manufactured, and standard universal fluid power components for the next generation of multi-functional, autonomous soft systems.

A self-powered soft triboelectric-electrohydrodynamic pump

Soft pumps have the potential to transform industries including soft robotics, wearable devices, microfluidics and biomedical devices, but their efficiency and power supply limitations hinder prolonged operation. Here, we report a self-powered triboelectric-electrohydrodynamic pump, which combines a soft electrohydrodynamic pump driven by an electrostatic generator, specifically a triboelectric nanogenerator. The triboelectric nanogenerator collects ambient energy and converts it into high-voltage power source, allowing it to self-power an electrohydrodynamic pump and thus eliminating the need for external power supply. Using power management circuit, geometric shape optimization, and stacking methods, we achieve a maximum pressure of 4.49 kPa and a maximum flow rate of 502 mL/min. We demonstrate the pump's versatility in applications such as self-powered soft actuators, oil pumping in microfluidics, and oil purification. The triboelectric-electrohydrodynamic pump holds promising applications, and offers new insights for the development of fully self-powered systems.

Printing Untethered Self-Reconfigurable, Self-Amputating Soft Robots from Recyclable Self-Healing Fibers

Regarding the challenge of self-reconfiguration and self-amputation of soft robots, existing studies mainly focus on modular soft robots and connection methods between modules. Different from these studies, this study focus on the behavior of individual soft robots from a material perspective. Here, a kind of soft fibers, which consist of hot melt adhesive particles, magnetizable microparticles, and ferroferric oxide microparticles embedded in a thermoplastic polyurethane matrix are proposed. The soft fibers can achieve wireless self-healing and reversible bonding of the fibers by eddy current heating and can be actuated by magnetic fields. Moreover, the soft fibers are recyclable and printable. Building on this material foundation, an integrated material-structure-actuation printing strategy using soft fibers for the design and fabrication of soft robots are reported. The robots printed by this strategy can achieve their untethered motions and wireless self-healing. Soft gripper, soft crawling robot, and soft multi-legged robot, are then fabricated which demonstrates the self-healing, self-reconfigurable, self-amputating, and sustainable performances of soft robots so as to adapt to different environments and tasks. This integrated material-structure-actuation printing strategy using soft fibers is universal, easy to implement, and mass-manufactured, opening a door for sustainable, eco-friendly, untethered, self-reconfigurable, self-amputating soft robots.

Design and Validation of a Biomimetic Leg-Claw Mechanism Capable of Perching and Grasping for Multirotor Drones

Multirotor drones are widely used in fields such as environmental monitoring, agricultural inspection, and package delivery, but they still face numerous challenges in durability and aerial operation capabilities. To address these issues, this paper presents a biomimetic leg-claw mechanism (LCM) inspired by the biomechanics of birds. The claw of the LCM adopts a bistable gripper design that can rapidly close through external impact or actively close via the coordination of internal mechanisms. Additionally, its foldable, parallelogram-shaped legs bend under external forces, stretching the main tendon. A ratchet and pawl mechanism at the knee joint locks the leg in the bent position, thereby enhancing the gripping force of the claw. This paper calculates and experimentally verifies the degrees of freedom in different states, the forces required to open and close the gripper, the application scenarios of active and passive grasping, and the maximum load capacity of the mechanism. Furthermore, perching experiments demonstrate that the LCM enables the drone to perch stably on objects of varying diameters.

Programmable Chemical Reactions Enable Ultrastrong Soft Pneumatic Actuation

Soft pneumatic actuation is widely used in wearable devices, soft robots, artificial muscles, and surgery machines. However, generating high-pressure gases in a soft, controllable, and portable way remains a substantial challenge. Here, a class of programmable chemical reactions that can be used to controllably generate gases with a maximum pressure output of nearly 6 MPa is reported. It is proposed to realize the programmability of the chemical reaction process using thermoelectric material with programmable electric current and employing preprogrammed reversible chemical reactants. The programmable chemical reactions as soft pneumatic actuation can be operated independently as miniature gas sources (∼20-100 g) or combined with arbitrary physical structures to make self-contained machines, capable of generating unprecedented pressures of nearly 6 MPa or forces of about 18 kN in a controllable, portable, and silent manner. Striking demonstrations of breaking a brick, a marble, and concrete blocks, raising a sightseeing car, and successful applications in artificial muscles and soft assistive wearables illustrate tremendous application prospects of soft pneumatic actuation via programmable chemical reactions. The study establishes a new paradigm toward ultrastrong soft pneumatic actuation.

Electricity-Driven Strategies for Bioinspired Multifunctional Swimming Marangoni Robots Based on Super-Aligned Carbon Nanotube Composites

Marangoni actuators that are propelled by surface tension gradients hold significant potential in small-scale swimming robots. Nevertheless, the release of "fuel" for conventional chemical Marangoni actuators is not easily controllable, and the single swimming function also limits application areas. Constructing controllable Marangoni robots with multifunctions is still a huge challenge. Herein, inspired by water striders, electricity-driven strategies are proposed for a multifunctional swimming Marangoni robot (MSMR), which is fabricated by super-aligned carbon nanotube (SACNT) and polyimide (PI) composite. The MSMR consists of a Marangoni actuator and air-ambient actuators. Owing to the temperature gradient generated by the electrical stimulation on the water surface, the Marangoni actuators can swim controllably with linear, turning, and rotary motions, mimicking the walking motion of water striders. In addition, the Marangoni actuators can also be driven by light. Importantly, the air-ambient actuators fabricated by SACNT/PI bilayer structures demonstrate the function of grasping objects on the water surface when electrically Joule-heated, mimicking the predation behavior of water striders. With the synergistic effect of the Marangoni actuator and air-ambient actuators, the MSMR can navigate mazes with tunnels and grasp objects. This research will provide a new inspiration for smart actuators and swimming robots.

Single-Electrode Electrostatic Repulsion Phenomenon for Remote Actuation and Manipulation

One of the fundamental principles of electrostatics is that an uncharged object will be attracted to a charged object through electrostatic induction as the two approaches one another. We refer to the charged object as a single electrode and examine the scenario where a positive voltage is applied. Because of electrostatic induction phenomenon, single-electrode electrostatics only generates electrostatic attraction forces. Here, we discover that single-electrode electrostatics can generate electrostatic repulsion forces and define this new phenomenon as single-electrode electrostatic repulsion phenomenon. We investigate the fundamental electrostatic phenomena, giving a curve of electrostatic force versus voltage and then defining 3 regions. Remote actuation and manipulation are essential technologies that are of enormous concern, with tweezers playing an important role. Various tweezers designed on the basis of external fields of optics, acoustics, and magnetism can be used for remote actuation and manipulation, but some inherent drawbacks still exist. Tweezers would benefit greatly from our discovery in electrostatics. On the basis of this discovery, we propose the concept of electrostatic tweezers, which can achieve noncontact and remote actuation and manipulation. Experimental characterizations and successful applications in metamaterials, robots, and manipulating objects demonstrated that electrostatic tweezers can produce large deformation rates (>6,000%), fast actuation (>100 Hz), and remote manipulating distance (~15 cm) and have the advantages of simple device structure, easy control, lightweight, no dielectric breakdown, and low cost. Our work may deepen people's understanding of single-electrode electrostatics and opens new opportunities for remote actuation and manipulation.

Powerful UAV manipulation via bioinspired self-adaptive soft self-contained gripper

Existing grippers for unmanned aerial vehicle (UAV) manipulation have persistent challenges, highlighting a need for grippers that are soft, self-adaptive, self-contained, easy to control, and lightweight. Inspired by tendril plants, we propose a class of soft grippers that are voltage driven and based on winding deformation for self-adaptive grasping. We design two types of U-shaped soft eccentric circular tube actuators (UCTAs) and propose using the liquid-gas phase-transition mechanism to actuate UCTAs. Two types of UCTAs are separately cross-arranged to construct two types of soft grippers, forming self-contained systems that can be directly driven by voltage. One gripper inspired by tendril climbers can be used for delicate grasping, and the other gripper inspired by hook climbers can be used for strong grasping. These grippers are ideal for deployment in UAVs because of their self-adaptability, ease of control, and light weight, paving the way for UAVs to achieve powerful manipulation with low positioning accuracy, no complex grasping planning, self-adaptability, and multiple environments.

Untethered soft actuators for soft standalone robotics

Soft actuators produce the mechanical force needed for the functional movements of soft robots, but they suffer from critical drawbacks since previously reported soft actuators often rely on electrical wires or pneumatic tubes for the power supply, which would limit the potential usage of soft robots in various practical applications. In this article, we review the new types of untethered soft actuators that represent breakthroughs and discuss the future perspective of soft actuators. We discuss the functional materials and innovative strategies that gave rise to untethered soft actuators and deliver our perspective on challenges and opportunities for future-generation soft actuators.

Development of an Anthropomorphic Soft Manipulator with Rigid-Flexible Coupling for Underwater Adaptive Grasping

Inspired by human hands and wrists, an anthropomorphic soft manipulator (ASM) driven by water hydraulics is proposed for underwater operations and exploration. Compared with traditional rigid manipulator, ASM has highly evolved grasping ability with better flexibility and adaptability, while it has better load capacity, grasping ability, and flexibility in comparison with the pneumatic gripper. ASM wrist is composed of rigid-flexible coupling structure with three bellows and a spindle, which generates continuous wrist pitching. The linear elongate characteristics of bellows and pitching performance of ASM wrist are simulated by finite element modeling (FEM) method and tested experimentally. The mathematical model of bending deformation for the water hydraulic soft gripper (WHSG) is established. The bending deformation and contact force of WHSG are simulated by FEM and measured experimentally. The ASM prototype is fabricated, and the grasping experiments in the air and underwater are conducted. It is confirmed that the developed ASM can switch between standard and expanded grasping position to adopt and grasp objects of different shapes and dimensions. And living animals with rough or smooth surfaces such as turtle and carp can also be caught harmlessly. ASM also exhibits preferable adaptability when the objects are out of grasping range or deviating from the grasping center. This study confirms that the developed ASM has enormous application potentials and broader prospects in the field of underwater operation, underwater fishing, underwater sampling, etc.

Self-protection soft fluidic robots with rapid large-area self-healing capabilities

Soft fluidic robots have attracted a lot of attention and have broad application prospects. However, poor fluidic power source and easy to damage have been hindering their development, while the lack of intelligent self-protection also brings inconvenience to their applications. Here, we design diversified self-protection soft fluidic robots that integrate soft electrohydrodynamic pumps, actuators, healing electrofluids, and E-skins. We develop high-performance soft electrohydrodynamic pumps, enabling high-speed actuation and large deformation of untethered soft fluidic robots. A healing electrofluid that can form a self-healed film with excellent stretchability and strong adhesion is synthesized, which can achieve rapid and large-areas-damage self-healing of soft materials. We propose multi-functional E-skins to endow robots intelligence, making robots realize a series of self-protection behaviors. Moreover, our robots allow their functionality to be enhanced by the combination of electrodes or actuators. This design strategy enables soft fluidic robots to achieve their high-speed actuation and intelligent self-protection, opening a door for soft robots with physical intelligence.

A Soft Reconfigurable Circulator Enabled by Magnetic Liquid Metal Droplet for Multifunctional Control of Soft Robots

Integrated control circuits with multiple computation functions are essential for soft robots to achieve diverse complex real tasks. However, designing compliant yet simple circuits to embed multiple computation functions in soft electronic systems above the centimeter scale is still a tough challenge. Herein, utilizing smooth cyclic motions of magnetic liquid metal droplets (MLMD) in specially designed and surface-modified circulating channels, a soft reconfigurable circulator (SRC) consisting of three simple and reconfigurable basic modules is described. Through these modules, MLMD can utilize their conductivity and extreme deformation capabilities to transfer their simple cyclic motions as input signals to programmable electrical output signals carrying computing information. The obtained SRCs make it possible for soft robots to perform complex computing tasks, such as logic, programming, and self-adaptive control (a combination of programming and feedback control). Following, a digital logic-based grasping function diagnosis, a locomotion reprogrammable soft car, and a self-adaptive control-based soft sorting gripper are demonstrated to verify SRCs' capabilities. The unique attributes of MLMD allow complex computations based on simple configurations and inputs, which provide new ways to enhance soft robots' computing capabilities.

A versatile jellyfish-like robotic platform for effective underwater propulsion and manipulation

Underwater devices are critical for environmental applications. However, existing prototypes typically use bulky, noisy actuators and limited configurations. Consequently, they struggle to ensure noise-free and gentle interactions with underwater species when realizing practical functions. Therefore, we developed a jellyfish-like robotic platform enabled by a synergy of electrohydraulic actuators and a hybrid structure of rigid and soft components. Our 16-cm-diameter noise-free prototype could control the fluid flow to propel while manipulating objects to be kept beneath its body without physical contact, thereby enabling safer interactions. Its against-gravity speed was up to 6.1 cm/s, substantially quicker than other examples in literature, while only requiring a low input power of around 100 mW. Moreover, using the platform, we demonstrated contact-based object manipulation, fluidic mixing, shape adaptation, steering, wireless swimming, and cooperation of two to three robots. This study introduces a versatile jellyfish-like robotic platform with a wide range of functions for diverse applications.

Bioinspired Self-Resettable Hydrogel Actuators Powered by a Chemical Fuel

The movements of soft living tissues, such as muscle, have sparked a strong interest in the design of hydrogel actuators; however, so far, typical manmade examples still lag behind their biological counterparts, which usually function under nonequilibrium conditions through the consumption of high-energy biomolecules and show highly autonomous behaviors. Here, we report on self-resettable hydrogel actuators that are powered by a chemical fuel and can spontaneously return to their original states over time once the fuels are depleted. Self-resettable actuation originates from a chemical fuel-mediated transient change in the hydrophilicity of the hydrogel networks. The actuation extent and duration can be programmed by the fuel levels, and the self-resettable actuation process is highly recyclable through refueling. Furthermore, various proof-of-concept autonomous soft robots are created, resembling the movements of soft-bodied creatures in nature. This work may serve as a starting point for the development of lifelike soft robots with autonomous behaviors.

Flexible Electronics and Devices as Human-Machine Interfaces for Medical Robotics

Medical robots are invaluable players in non-pharmaceutical treatment of disabilities. Particularly, using prosthetic and rehabilitation devices with human-machine interfaces can greatly improve the quality of life for impaired patients. In recent years, flexible electronic interfaces and soft robotics have attracted tremendous attention in this field due to their high biocompatibility, functionality, conformability, and low-cost. Flexible human-machine interfaces on soft robotics will make a promising alternative to conventional rigid devices, which can potentially revolutionize the paradigm and future direction of medical robotics in terms of rehabilitation feedback and user experience. In this review, the fundamental components of the materials, structures, and mechanisms in flexible human-machine interfaces are summarized by recent and renowned applications in five primary areas: physical and chemical sensing, physiological recording, information processing and communication, soft robotic actuation, and feedback stimulation. This review further concludes by discussing the outlook and current challenges of these technologies as a human-machine interface in medical robotics.

Electrically Controlled Aquatic Soft Actuators with Desynchronized Actuation and Light-Mediated Reciprocal Locomotion

Soft-bodied aquatic invertebrates can overcome hydrodynamic resistance and display diverse locomotion modes in response to environmental cues. Exploring the dynamics of locomotion from bioinspired aquatic actuators will broaden the perspective of underwater manipulation of artificial systems in fluidic environments. Here, we report a multilayer soft actuator design based on a light-driven hydrogel and a laser-induced graphene (LIG) actuator, minimizing the effect of the time delay by a monolithic hydrogel-based system while maintaining shape-morphing functionality. Moreover, different time scales in the response of actuator materials enable a real-time desynchronization of energy inputs, holding great potential for applications requiring desynchronized stimulation. This hybrid design principle is ultimately demonstrated with a high-performance aquatic soft actuator possessing an underwater walking speed of 0.81 body length per minute at a relatively low power consumption of 3 W. When integrated with an optical sensor, the soft actuator can sense the variation in light intensity and achieve mediated reciprocal motion. Our proposed locomotion mechanism could inspire other multilayer soft actuators to achieve underwater functionalities at the same spatiotemporal scale. The underwater actuation platform could be used to study locomotion kinematics and control mechanisms that mimic the motion of soft-bodied aquatic organisms.

A Soft Electro-Hydraulic Pneumatic Actuator with Self-Sensing Capability toward Multi-Modal Haptic Feedback

Haptic feedback is appealing for achieving the realistic perception of environmental changes for human bodies in human–computer interaction fields. However, existing haptic actuators have some hurdles such as single mode, poor compatibility, or incomplete tactile information. In this study, we proposed a novel way to generate haptic feedback by designing a soft electro-hydraulic pneumatic actuator (SEHPA) with dual drive modes. The SEHPA was structured with silicone films, a silicone air chamber, flexible electrodes, and an insulating liquid dielectric for good human–machine compatibility. The SEHPA had the advantages of high output force (1.5 N at 10 kPa) and displacement (4.5 mm at 5 kPa), as well as various haptic notifications (0~400 Hz vibration). The electro-hydraulic drive method realized smooth output force changes at the millinewton level (0~40 mN) and output displacement changes at the micron level (0~800 μm), which further enriched the details of the tactile experience. In addition, the self-sensing capability of the SEHPA can be dedicated to monitoring and ensuring precise output. The SEHPAs can be potentially mounted on the fingertips to provide accurate tactile sensation once the manipulator touches an object through teleoperation. More invisible information can also be obtained by customizing various haptic notifications. The excellent response behavior and accurate tactile haptic feedback demonstrate the candidate for teleoperation fields.

Course Control of a Manta Robot Based on Amplitude and Phase Differences

Due to external interference, such as waves, the success of underwater missions depends on the turning performance of the vehicle. Manta rays use two broad pectoral fins for propulsion, which provide better anti-interference ability and turning performance. Inspired by biological yaw modes, we use the phase difference between the pectoral fins to realize fast course adjustment and the amplitude difference to realize precise adjustment. We design a bionic robot with pectoral fins and use phase oscillators to realize rhythmic motion. An expected phase difference transition equation is introduced to realize a fast and smooth transition of the output, and the parameters are adjusted online. We combine the phase difference and amplitude difference yaw modes to realize closed-loop course control. Through course interference and adjustment experiments, it is verified that the combined mode is more effective than a single mode. Finally, a rectangular trajectory swimming experiment demonstrates continuous mobility of the robot under the combined mode.