Applications In Soft Robotics Research Articles

Multivapor-Responsive Controlled Actuation of Starch-Based Soft Actuators.

Multivapor-responsive biocompatible soft actuators have immense potential for applications in soft robotics and medical technology. We report fast, fully reversible, and multivapor-responsive controlled actuation of a pure cassava-starch-based film. Notably, this starch-based actuator sustains its actuated state for over 60 min with a continuous supply of water vapor. The durability of the film and repeatability of the actuation performance have been established upon subjecting the film to more than 1400 actuation cycles in the presence of water vapor. The starch-based actuators exhibit intriguing antagonistic actuation characteristics when exposed to different solvent vapors. In particular, they bend upward in response to water vapor and downward when exposed to ethanol vapor. This fascinating behavior opens up new possibilities for controlling the magnitude and direction of actuation by manipulating the ratio of water to ethanol in the binary solution. Additionally, the control of the bending axis of the starch-based actuator, when exposed to water vapor, is achieved by imprinting-orientated patterns on the surface of the starch film. The effect of microstructure, postsynthesis annealing, and pH of the starch solution on the actuation performance of the starch film is studied in detail. Our starch-based actuator can lift 10 times its own weight upon exposure to ethanol vapor. It can generate force ∼4.2 mN upon exposure to water vapor. To illustrate the vast potential of our cassava-starch-based actuators, we have showcased various proof-of-concept applications, ranging from biomimicry to crawling robots, locomotion near perspiring human skin, bidirectional electric switches, ventilation in the presence of toxic vapors, and smart lifting systems. These applications significantly broaden the practical uses of these starch-based actuators in the field of soft robotics.

Viscoelastic Dynamics of Photothermal‐Responsive Liquid Crystal Elastomer Fibers

AbstractLiquid crystal elastomers (LCEs) with photo‐responsive properties, typically driven by either photochemical or photothermal mechanisms, have found extensive applications as, for example, actuators in soft robots. However, intricate temperature‐dependent viscoelasticity of LCEs poses a challenge, leading to a notable gap in the domain of dynamic models for photothermal‐responsive LCE (PTR‐LCE) fibers. Here, a fundamental framework is proposed for accurate modeling and real‐time simulations of PTR‐LCE fiber dynamics. The PTR‐LCE fiber is described as a one‐dimensional (1D) string model that decomposes the fiber deformation into active and passive parts, which are characterized by an order parameter and a temperature‐dependent linear viscoelasticity model, respectively. Then, independent experimental measurements of model parameters are conducted, and a numerical algorithm is developed to solve the model, which is validated for convergence, time efficiency, and accuracy. Finally, the model is employed to simulate both open‐loop and Proportional‐Integral‐Derivative (PID) control of actuators made of PTR‐LCE fibers. The results confirm the advantages of this model over previous models. This work not only reveals the physical mechanisms underlying the PTR‐LCE fiber dynamic behaviors but also provides inspirations for more efficient and precise soft robotic applications.

Self-deployable contracting-cord metamaterials with tunable mechanical properties.

Recent advances in active materials and fabrication techniques have enabled the production of cyclically self-deployable metamaterials with an expanded functionality space. However, designing metamaterials that possess continuously tunable mechanical properties after self-deployment remains a challenge, notwithstanding its importance. Inspired by push puppets, we introduce an efficient design strategy to create reversibly self-deployable metamaterials with continuously tunable post-deployment stiffness and damping. Our metamaterial comprises contracting actuators threaded through beads with matching conical concavo-convex interfaces in networked chains. The slack network conforms to arbitrary shapes, but when actuated, it self-assembles into a preprogrammed configuration with beads gathered together. Further contraction of the actuators can dynamically tune the assembly's mechanical properties through the beads' particle jamming, while maintaining the overall structure with minimal change. We show that, after deployment, such metamaterials exhibit pronounced tunability in bending-dominated configurations: they can become more than 35 times stiffer and change their damping capability by over 50%. Through systematic analysis, we find that the beads' conical angle can introduce geometric nonlinearity, which has a major effect on the self-deployability and tunability of the metamaterial. Our work provides routes towards reversibly self-deployable, lightweight, and tunable metamaterials, with potential applications in soft robotics, reconfigurable architectures, and space engineering.

Autonomous self-healing and highly stretchable polymer maltose polyborosiloxane for improving soft electronics and soft robots

This study showcases PM PBS's remarkable blend of stretchability, swift self-healing, and multifunctionality, making it a promising choice for various applications in soft robotics, wearable technology, and more.

Sculpting liquid metal stabilized interfaces: a gateway to liquid electronics.

Liquid electronics have potential applications in soft robotics, printed electronics, and healable electronics. The intrinsic shortcomings of solid-state electronics can be offset by liquid conductors. Alloys of gallium have emerged as transformative materials for liquid electronics owing to their intrinsic fluidity, conductivity, and low toxicity. However, sculpting liquid metal or its composites into a 3D architecture is a challenging task. To tackle this issue, herein, we explored the interfacial chemistry of metal ions and tannic acid (TA) complexation at a liquid-liquid interface. First, we established that an MIII-TA network at the liquid-liquid interface could structure liquid in liquid by jamming the interfacial film. The surface coverage of the droplet largely depends on the concentration of metal ions, oxidation state of metal ions and pH of the surrounding environment. Further extending the approach, we demonstrated that TA-functionalized gallium nanoparticles (Ga NPs) can also sculpt liquid droplets in the presence of transition metal ions. Finally, a mold-based free-standing 3D architecture is obtained using the interfacial reaction and interfacial crowding of a metal-phenolate network. Conductivity measurement reveals that these liquid constructs can be used for low-voltage electronic applications, thus opening the door for liquid electronics.

Bio-inspired facile strategy for programmable osmosis-driven shape-morphing elastomer composite structures.

Achieving programmable and reversible deformations of soft materials is a long-standing goal for various applications in soft robotics, flexible electronics and many other fields. Swelling-induced shape morphing has been intensively studied as one of the potential mechanisms. However, achieving an extremely large swelling ratio (>1000% in volume) remains challenging with existing swellable soft materials (e.g., hydrogels and water-swellable rubbers). Inspired by the shape change enabled by the osmosis-driven swelling in living organisms, herein, we report a polymer composite system composed of fine sodium chloride (NaCl) particles embedded in Ecoflex00-10 polymer. This Ecoflex00-10/NaCl polymer composite can achieve controllable volumetric swelling up to 3000% while maintaining a relatively high elastic stiffness. We demonstrate that this swellable polymer composite can serve as an active component to drive the shape morphing of various structures. By controlling the geometric design and the fraction of the NaCl particle, morphing structures capable of deforming sequentially are created. Finally, by encapsulating 3D printed polymer composite patterns using water-permeable PDMS membrane, a programmable braille with visual and tactile regulation is demonstrated for the purpose of information encryption. Our study provides a facile approach to generate customizable shape-morphing structures, aiming to broaden the range of techniques and applications for morphing devices.

A Wrist-Inspired Magneto-Pneumatic Hybrid-Driven Soft Actuator with Bidirectional Torsion.

A novel wrist-inspired soft actuator, which is driven by a magneto-pneumatic hybrid system and based on a Kresling origami unit, is proposed. The geometric model, kinematic analysis model, and quasistatic analysis model of the Kresling origami unit are presented. A key focus is on the formulation and investigation of the variation in rotation angle using the kinematic analysis model. A wrist-inspired soft actuator is designed, and its quasistatic characteristics are validated through various experiments. The paper proposes an innovative magneto-pneumatic hybrid actuation method, capable of achieving bidirectional torsion. This actuation method is experimentally validated, demonstrating the actuator's ability to maintain 3 steady states and its capability for bidirectional torsion deformation. Furthermore, the paper highlights the potential of the Kresling origami unit in designing soft actuators capable of achieving large rotation angles. For instance, an actuator with 6 sides (n = 6) is shown to achieve a rotation angle of 239.5°, and its rotation ratio exceeds 277°, about twice the largest one reported in other literature. The actuator offers a practical and effective solution for bidirectional torsion deformation in soft robotic applications.

Silicone-layered waterproof electrohydraulic soft actuators for bio-inspired underwater robots.

Electrohydraulic soft actuators are a promising soft actuation technology for constructing bio-inspired underwater robots owing to the features of this technology such as large deformations and forces, fast responses, and high electromechanical efficiencies. However, this actuation technology requires high voltages, thereby limiting the use of these actuators in water and hindering the development of underwater robots. This paper describes a method for creating bio-inspired underwater robots using silicone-layered electrohydraulic soft actuators. The silicone layer functions as an insulator, enabling the application of high voltages underwater. Moreover, bending and linear actuation can be achieved by applying the silicone layers on one or both sides of the actuator. As a proof of concept, bending and linear actuators with planar dimensions of 20 mm × 40 mm (length × width) are fabricated and characterized. Underwater actuation is observed in both types of actuators. The bending actuators exhibit a bending angle and blocked force of 39.0° and 9.6 mN, respectively, at an applied voltage of 10 kV. Further, the linear actuators show a contraction strain and blocked force of 6.6% and 956.1 mN, respectively, at an applied voltage of 10 kV. These actuators are tested at a depth near the surface of water. This ensured that they can operate at least at that depth. The actuators are subsequently used to implement various soft robotic devices such as a ray robot, a fish robot, a water-surface sliding robot, and a gripper. All of the robots exhibit movements as expected; up to 31.2 mm/s (0.91 body length/s) of locomotion speed is achieved by the swimming robots and a retrieve and place task is performed by the gripper. The results obtained in this study indicate the successful implementation of the actuator concept and its high potential for constructing bio-inspired underwater robots and soft robotics applications.

Robust Control of Dielectric Elastomer Smart Actuator for Tracking High-Frequency Trajectory

Dielectric elastomer smart actuator (DESA) has shown great potentials in soft robot applications. The control of the DESA is one of key issues for soft robots. However, the precise control of the DESA is a challenge work, especially when tracking high-frequency trajectories and guaranteeing a certain robustness. To this end, this paper presents a robust tracking control method for a DESA to track various high-frequency trajectories. Firstly, to characterize the complex nonlinear properties (including the quadratic input, asymmetric and rate-dependent hysteresis, as well as creep) of the DESA, its dynamic model is built by combining a square function module, a modified Prandtl-Ishlinskii (P-I) hysteresis model and a linear system. Subsequently, by combining the inverse of the modified P-I hysteresis model with a square root function module, the quadratic input and asymmetric hysteresis properties of the DESA are compensated to reduce tracking the control error. Since model uncertainties and external disturbances are unavoidable in practical applications, a robust controller is designed to achieve the tracking control of the DESA, the controller also guarantees the robustness of the control system. In the end, the effectiveness of the proposed control method is demonstrated through a series of tracking control experiments with different high-frequency trajectories, whose maximal frequency is 8 (Hz). The root- mean-square errors of all experimental results are lower than 1.5%, which proves that the presented method is remarkable from the respective of the practical application.

Self-assembled biomolecular soft materials and their physical properties

Self-assembling biomolecular soft materials are a novel type of soft matter formed through the self-assembly process by using biomolecules or biomolecular building blocks. The characteristics of bio-sourced origin and assembly driven by weak interactions endow these materials with advantages such as high biocompatibility, reversible assembly, dynamic responsiveness, and controllable microstructures. These properties offer immense potential for development in fields such as biomedicine, tissue engineering, and flexible sensing. This paper concisely reviews the fundamental construction principles of self-assembling biomolecular soft materials and discusses three categories, i.e. nanomaterials, gel materials, and composite materials, by using amino acids and peptides as examples of assembly units. The specific self-assembly molecular mechanisms, material construction strategies, and functional application scenarios of these materials are elucidated. We anticipate that the research on self-assembling soft matter biomolecular materials will evolve from exploring structural units and measuring properties to customizing multifunctional properties and integrating advanced applications. This will lead to the development of novel composite intelligent biomolecular soft matter materials, and further promoting their applications in biomedicine, organic semiconductors, and soft robotics.

Bioinspired layered hydrogel actuator via L-ascorbic acid-triggered interfacial self-growing from stiff hydrogel

Stimuli-response layered hydrogel actuators are highly attractive in broad applications of soft robots, intelligent devices and etc., owing to softness, asymmetric responsiveness and deformability. However, current layered hydrogel actuators suffer...

Unlocking the potential of self-healing and recyclable ionic elastomers for soft robotics applications.

In the field of soft robotics, current materials face challenges related to their load capacity, durability, and sustainability. Innovative solutions are required to address these problems beyond conventional strategies, which often lack long-term ecological viability. This study aims to overcome these limitations using mechanically robust, self-healing, and recyclable ionic elastomers based on carboxylated nitrile rubber (XNBR). The designed materials exhibited excellent mechanical properties, including tensile strengths (TS) exceeding 19 MPa and remarkable deformability, with maximum elongations (EB) over 650%. Moreover, these materials showed high self-healing capabilities, with 100% recovery efficiency of TS and EB at 110 °C after 3 to 5 h, and full recyclability, preserving their mechanical performance even after three recycling cycles. Furthermore, they were also moldable and readily scalable. Tendon-driven soft robotic grippers were successfully developed out of ionic elastomers, illustrating the potential of self-healing and recyclability in the field of soft robotics to reduce maintenance costs, increase material durability, and improve sustainability.

Pre-programmable pneumatic actuator: leveraging mechanical anisotropy of nonwoven fabrics with an integrated tensile sensor.

The emergence of flexible fabric-based pneumatic actuators (FPAs) with pre-programmable motion capabilities, enhanced security and versatile interaction features significantly advances the construction of sophisticated soft robotic systems, owing to their enhanced security and versatile interaction features. Despite these promising attributes, the commercial viability of FPA products faces a considerable amount of challenges, primarily stemming from the scarcity of highly deformable fabric structures and the availability of industrial fabrication approaches. Taking inspiration from the anisotropic nature of lobster antennae, we propose a scalable and economical strategy to fabricate functional FPAs using nonwoven fabric material with superior mechanical anisotropy. This innovative method involves the adoption of tunable inelastic constrained wires sewn onto extensible nonwoven fabrics with regular wrinkles. This nonwoven fabric-based pneumatic actuator (NFPA) demonstrates specific motion profiles with curvature of over 0.6 cm-1 and output forces of over 140 cN under adjustable pressure conditions. Guided by the constrained wire combinations, NFPA enables diverse programmable motions like spiraling, assistance, and grasping. Furthermore, NFPA incorporated with specific sensors exhibits significant potential in wearable devices with real-time environmental detection for rehabilitation applications. Our work contributes a distinctive insight into the design of programmable NFPAs and enlightens an arena toward versatile soft robotic applications.

Tube Mechanism With 3-Axis Rotary Joints Structure to Achieve Variable Stiffness Using Positive Pressure

Studies on soft robotics have explored mechanisms of switching the stiffness of a robot structure. The hybrid soft-rigid approach, which combines soft materials and high-rigidity structures, is the most commonly-used method for the variable stiffness mechanism. The positive-pressurization method, in particular, has attracted significant attention in recent years as it can remove the limit on the driving pressure. Moreover, it can change the shape holding force according to the value of internal pressure. In this study, a variable stiffness mechanism, consisting of 3-axis rotary ball joints and a single chamber, is devised via frictional force using positive pressure. The prototype can change joint angles arbitrarily when not pressurized and can hold joint angles when a positive pressure is applied. By using a theoretical model of the torque required to hold the joint angle, we simulated the holding torque using finite element modeling analysis and measured the holding torque in the pitch and roll directions when internal pressure was applied. Based on the interaction of the theoretical model, measurement, and FEM analysis, it was confirmed that the value of the holding torque in the roll direction was approximately π/2 times larger than that in the pitch direction for each value of the internal pressure. Further, we evaluated the FEM value, theoretical value, and measured value of holding torque by numerical comparison with each other. We believe that our approach will aid the design of effective stiffening mechanisms for soft robotics applications.

Soft Medical Robots and Probes: Concise Survey of Current Advances

Soft robotics has emerged as a new branch of robotics gaining huge research interest in recent decades. Owning intrinsic advantages such as compliance and safety, soft robots are closely associated with the medical requirements of medical robots. This review is written to overview advances in the medical applications of soft robots, either for readers primarily familiar with traditional medical systems, or for researchers planning to develop soft robots for medical applications. Recent publications related to soft medical robots were reviewed to represent the state’, ’of’, ’the’, ’art advances in this field. The review tends to compress the scope to trunk’, ’shaped soft robots and appraise the status of soft robots and their distance from clinical use. Several papers related to the construction and capabilities of soft robots were referenced. Roughly 190 related articles published in the current period from 2018 to the publication date (representing almost 90% of the references to the theme totally identified) were reviewed. Structure of soft robots, advances in technology, and the aptitudes in medical applications were discussed. The trunk’, ’like soft robots conspicuously are proposed for applications including robot assisted surgery where a probe is inserted into the human body. Such robots are also present in other medical robots as actuators. The literature shows that different methods are used to fabricate soft robots and employ them in different robotics tasks including positioning, grasping, and force exertion. Noticeably, such studies were done in robotics laboratories, dealing with robotics engineering problems. This review suggests that the technology is actively developing, but further focus on specific medical applications is required to fill the gap between soft robotics and its clinical use.

Unidirectional Freezing of Polymer Solution Droplets.

Ice templating provides a means of generating textures with a well-defined topography. Recent applications involve the freezing of water droplets, with or without colloids, on flat or textured surfaces. An interesting feature of water droplets freezing on a substrate is the formation of a pointy tip at a constant angle, regardless of the substrate temperature, surface energy, or droplet volume. Here, by adding the polymer to water, we demonstrate how to manipulate and even prevent the formation of such an icy tip. We find that the sharpness of the tip decreases with increasing polymer concentration until completely disappearing above the overlap concentration, while the total freezing time increases concomitantly. Building on these observations, we combined simple geometrical arguments with heat flux measurements to model and connect the spatial and temporal evolution of polymer droplets under unidirectional freezing. Together our results provide new ways to control the shape of frozen droplets for ice templating or microstructure fabrication, with applications in tissue engineering, separation membranes, and soft robotics.

Optimization of Graphene infused Natural Rubber Sensing Film and Polydimethylsiloxane for Flexible Pressure Sensor

A flexible and stretchable pressure sensor offers significant benefits in human-computer interaction, healthcare, and tactile sensing in robots. We present a novel study optimising Polydimethylsiloxane (PDMS) and graphene-infused unvulcanised natural rubber sensing film to increase sensor sensitivity and dielectric permittivity. By optimising the PDMS thickness uniformity, NR-G film’s impedance and capacitance-pressure loading response, it is possible to enhance the pressure sensor's sensitivity across a wide pressure range, covering human finger motion. With our synthesized homogenous 5wt% of NRG composite, a capacitance value of 193pF was achieved when applying pressure of 150 kPa at a frequency of 0.5 Hz. Excellent sensitivity and dielectric permittivity of 0.020 kPa-1 and 109.1, respectively, which is ~ 6.5 folds higher than pure NR. PDMS thickness of 300μm with ±3% uniformity was achieved using 90s spin time and 200rpm spin speed. This optimisation of sensing material and substrate is important in developing wearable sensors having applications in soft robotics, health monitoring electronics, and soft human-machine interfaces.

Pom Functionalized Ionogels with Tunable Optical, Mechanical, Electrical, and Sensory Properties

AbstractIonogels, with wide applications in tissue engineering, soft robotics, and flexible iontronic devices, require tunable optical, mechanical, and electrical properties for advanced functionality applications. Here, a facile strategy is reported to tune a set of properties of ionogels via tuning the redox states of the added polyoxometalate (POM) clusters. Upon external electrical stimuli, the POM clusters in the ionogels can be reversibly tuned from a transparent, oxidized state to a blue, reduced state. The redox states of the POM anions influence the POM‐polymer interactions, which promotes the in situ modulation of the ionogel properties reversibly over a large window: optical transparency from 91% to 7%, dissipated energy from 0.9 to 3.1 MJ m−3, elastic modulus from 1.5 to 2 MPa, conductivity from 1.6 × 10−4 to 2.2 × 10−4 S cm−1. Meanwhile, the sensory properties of the ionogels can be modulated simultaneously. For strain sensing and pressure sensing, the GF can be tuned from 2.3 to 7.2, and the sensitivity can be tuned from 0.8 to 1.2 kPa−1. Such an ionogel with tunable optical, mechanical, and electrical properties may find a variety of applications meeting specific demands. The POM functionalization strategy may also bring new insights into the design of the stimuli‐responsive ionogels.

Bending sensor using ionic liquid crystal elastomers as solid electrolyte of organic electrochemical transistors

ABSTRACT Organic Electrochemical Transistors (OECTs) have the potential to enable fully flexible, low-cost electronics. Here, we demonstrate that OECTs can be combined with ionic liquid crystal elastomers (iLCEs) to realise highly sensitive bending sensors. The transfer curve of the iLCE-based OECT shows opposite variation with upward and downward bending representing a directional sensitive strain sensor. The change in the drain current is 4 orders of magnitude larger than the flexo-ionic current. This high sensitivity is due to the OECT that amplifies the flexo-ionic current. iLCE-based OECTs therefore present a new class of curvature sensors that may find applications in soft robotics and biosensing.

Multi-pole magnetization of NdFeB magnetic elastomers via a programmable magnetic stamp inspired by movable type printing

Multi-pole magnetization is crucial for enhancing the magnetic field strength of magnetic films. Programmable multi-pole magnetization with adjustable pole pitch and covering thicknesses from submillimeter to millimeter are challenging tasks. This paper introduces a programmable magnetic stamp method inspired by movable printing. Demagnetization curves at various temperatures illustrate that NdFeB has lower coercivity when heated, making it easier to magnetize. SmCo magnets as high temperature resistant magnetic stamps provide enough external magnetic field. Heating transfers the magnetic pole distribution of magnetic stamps to the NdFeB film. Using this method, we magnetize the NdFeB magnetic film with a checkerboard pattern (interlaced N and S poles). The minimum width of the pole pitch is 1.3 mm. Comparing the measured magnetic field results with the simulation values of ANSYS Maxwell, the trends are relatively close. Furthermore, we investigate the magnetic field component (Bz) related to height and compare the differences between direct and reverse magnetization. Additionally, five magnetic patterns are customized using arranged SmCo magnet arrays. Notably, this study accomplishes multi-pole magnetization with up to 100 poles, covering a magnetic film thickness ranging from 100 µm to 1 mm. The proposed approach provides submillimeter/millimeter-thick NdFeB magnetic films that work as powerful flux sources and exhibit promising applications in magnetic tactile sensors and soft robots.