Biomimetic Soft Actuators Research Articles

Temperature-Adaptative Self-Oscillating Gels: Toward Autonomous Biomimetic Soft Actuators with Broad Operating Temperature Region.

Self-oscillating gel systems exhibiting an expanded operating temperature and accompanying functional adaptability are showcased. The developed system contains nonthermoresponsive main-monomers, such as N,N-dimethylacrylamide (DMAAm) or 2-acrylamido-2-methylpropane sulfonic acid (AMPS) or acrylamide (AAm) or 3-(methacryloylamino)propyl trimethylammonium chloride (MAPTAC). The gels volumetrically self-oscillate within the range of the conventional (20.0°C) and extended (27.0 and 36.5°C) temperatures. Moreover, the gels successfully adapt to the environmental changes; they beat faster and smaller as the temperature increases. The period and amplitude are also controlled by tuning the amount of main-monomers and N-(3-aminopropyl) acrylamide. Furthermore, the record amplitude in the bulk gel system consisting of polymer strand and cross-linker at 36.5°C is achieved (≈10.8%). The study shows new self-oscillation systems composed of unprecedented combinations of materials, giving the community a robust material-based insight for developing more life-like autonomous biomimetic soft robots with various operating temperatures and beyond.

Biomimetic shape-morphing actuators with controlled bending deformation and photo-mediated 3D shape programming for flexible smart devices

Biomimetic soft actuators with programmable morphing behaviors and remote actuations have drawn significant attention in recent years. In this work, we present the network architecture of a four-arm crystalline shape memory polymer actuator via efficient thiol-acrylate coupling of polycaprolactone precursor bearing crosslinkable methacrylate end-groups with pentaerythritol, followed by post-approach surface chemistry of polydopamine (PDA) nanospheres coating. The excellent photothermal transfer efficiency of the coated PDA can enable rapid temperature increase over the transition temperature of polymeric matrix and optically drive the shape morphings. Combined with built-in internal stress, anisotropic polymer chain relaxation of the strained thin actuator film would generate asymmetric contractions and thus causes controlled bending deformations via surface directing of an 532 nm green laser. Beyond this, the dynamic nature of transesterification reaction also provides the actuator film with reprogrammability. Remarkably, the morphing behaviors of a flexible plane film into various soft robots including 3D airplane and chiral helix were achieved under a 300 mW/cm2 simulated light irradiation. The results presented in this study clearly provide a new method for designing actuators with spatiotemporally programmable morphing behaviors and will pave way for the construction of flexible smart devices.

Ultrasensitive and robust mechanoluminescent living composites.

Mechanosensing, the transduction of extracellular mechanical stimuli into intracellular biochemical signals, is a fundamental property of living cells. However, endowing synthetic materials with mechanosensing capabilities comparable to biological levels is challenging. Here, we developed ultrasensitive and robust mechanoluminescent living composites using hydrogels embedded with dinoflagellates, unicellular microalgae with a near-instantaneous and ultrasensitive bioluminescent response to mechanical stress. Not only did embedded dinoflagellates retain their intrinsic mechanoluminescence, but with hydrophobic coatings, living composites had a lifetime of ~5 months under harsh conditions with minimal maintenance. We 3D-printed living composites into large-scale mechanoluminescent structures with high spatial resolution, and we also enhanced their mechanical properties with double-network hydrogels. We propose a counterpart mathematical model that captured experimental mechanoluminescent observations to predict mechanoluminescence based on deformation and applied stress. We also demonstrated the use of the mechanosensing composites for biomimetic soft actuators that emitted colored light upon magnetic actuation. These mechanosensing composites have substantial potential in biohybrid sensors and robotics.

Highly biomimetic triboelectric-generating soft actuator with a hollow bilayer structure for sensing, temperature-sensitive switching and high-temperature alarm

Biomimetic soft actuators have garnered significant attention due to their exceptional motion performance, which mimics the body structure of animals to deform upon stimulation. However, creating actuators that can generate electricity, emit light, and produce sound like animals remains a daunting challenge. Therefore, a triboelectric-generating soft actuator (TEG-SA) with a hollow bilayer structure that combines a triboelectric nanogenerator (TENG) with a liquid crystal elastomer (LCE) was prepared. The LCE is equipped with poly(vinylidene fluoride) (PVDF) electrospun film and nylon 6/6 film as electric friction layers. Upon deformation by heat, the LCE drives the PVDF and nylon 6/6 to rub together, generating electrical signals, enabling it to achieve self-sensing and obtain the relevant information of the stimulus. Furthermore, the electrical signal can be processed by electronic component and converted into light and sound to alarm for high temperature. The TEG-SA can switch between high-temperature disconnection and conduction modes by a facile position change. The integration of TENG with soft actuators enriches the design of highly bionic actuators, making it a framework for the development of intelligent soft actuators with more stimulus responses.

Morph-genetic bamboo-reinforced hydrogel complex for bio-mimetic actuator

Stimuli-responsive hydrogels are most promising for the fabrication of autonomous bio-mimetic soft actuators. However, their weak actuation forces and isotropic volume change hinder their practical utilization as versatile actuators, owing to their fragility. Herein, we used the morph-genetic method to fabricate anisotropic bamboo/poly(N-isopropylacrylamide) hydrogel (ABH) complex for use as soft actuator. First of all, the bamboo fiber structure provides an anisotropic framework for the ABH actuator to achieve precise deformational programmability. Secondly, benefiting from the ultra-high directional strength (110 MPa) of bamboo, ABH actuator exhibits sufficiently robust mechanical property, which generates a powerful actuating force. Lastly, owing to the regulation of bamboo sheet and PNIPAM hydrogel, the ABH actuator not only achieves ultra-fast response speed (825°/s of the bending speed), but also has excellent synergetic performance. We demonstrate several bio-mimetic actuating devices based on ABH actuator, inspired by the intricate motions of natural organisms, to highlight how the specific materials properties and their synergy can be systematically exploited for the rational design of soft actuators. Henceforth, it is anticipated that the development of hydrogel actuators could continue to benefit from the use of various naturally-anisotropic materials, such as shape-memory polymers or liquid crystals, for the preparation of further advanced hydrogel actuators by the morph-genetic method.

Bayesian design optimization of biomimetic soft actuators

The design of versatile soft actuators remains a challenging task, as it is a complex trade-off between robotic adaptability and structural complexity. Recently, researchers have used statistical and physical models to simulate the mechanical behavior of soft actuators. These simulations can help identify optimal actuator designs that fulfill specific robotic objectives. However, automated optimization of soft robots is a delicate balance between simplifying assumptions that reduce predictive fidelity and expensive simulations that limit design space exploration. Here we propose a generalized Bayesian optimization method to identify the designs of fiber-based biomimetic soft-robotic arms that minimize the actuation energy under arbitrary robotic control requirements. We use the reduced-order active filament theory as the overarching design paradigm and mechanical model, which enables a computationally robust and efficient optimization process. We evaluate the performance of our Bayesian optimization for a simple control objective in which the actuator has to reach a given target position. We show that our proposed optimization scheme outperforms a random-search baseline; it identifies more desirable designs faster and more frequently. Although we illustrate the performance of our approach for a single actuation problem, the derived method easily generalizes to the design optimization of fiber-based actuators under a large family of robotic applications.

Graphene oxide and low-density polyethylene based highly sensitive biomimetic soft actuators powered by multiple clean energies of humidity and light

A biomimetic soft actuator with ultrahigh sensitivity and multi-responsive characteristics is proposed, which can make full use of the clean energies of light and humidity in nature for various of bionic and engineering designs.

Solvent‐Driven Biomimetic Soft Sensors and Actuators

AbstractThe emergence of soft actuators that exhibit large, complex, programmable, and reversible shape deformation is of fundamental interest having potential applications in optics, medicals, and robotics fields. However, existing soft actuators are generally driven by only few given external stimuli such as temperature, humidity, or light which limit their interactions with their surroundings. Here, biomimetic soft actuators that respond to a variety of solvent vapors via programmable motion studied by Finite Element Modeling (FEM) are presented. A versatile micromachining process is used to fabricate these biomimetic soft actuators able to bend, curve, and twist in different manners according to their designs mimicking stamen, seed pots, and petals of Bauhinia variegate and Dendrobium orchids. The kinetic parameters of the transient response and recovery actuation are taken as the input feature in principal component analysis (PCA) to discriminate analyte molecules. Finally, to broaden the accessible 3D motions and thus functions of these smart actuators, an origami approach is employed to provide further flexibility and novel controlled structural changes in continuum structures such as snake‐like soft actuators, walkers, and grippers.

Fluid-driven hydrogel actuators with an origami structure

SummaryOwing to the innate good biocompatibility, tissue-like softness and other unique properties, hydrogels are of particular interest as promising compliant materials for biomimetic soft actuators. However, the actuation diversity of hydrogel actuators is always restricted by their structure design and fabrication methods. Herein, origami structures were introduced to the design of fluid-driven hydrogel actuators to achieve diverse actuation movements, and a facile fabrication strategy based on removable templates and inside-out diffusion-induced in situ hydrogel crosslinking was adopted. As a result, three types of modular cuboid actuator units (CAUs) achieved linear motion, bending, and twisting. Moreover, combinations of multiple CAUs achieved different actuation modes, including actuation decoupling, superposition, and reprogramming. The diverse actuation functionality would enable new possibilities in application fields for hydrogel soft actuators. Several simple application demos, such as grippers for grasping tasks and a multi-way circuit switch, demonstrated their potential for further applications.

Frontispiece: Thermo‐ and Mechanochromic Camouflage and Self‐Healing in Biomimetic Soft Actuators Based on Liquid Crystal Elastomers

Soft Actuators In their Research Article (e202115755), Hong Yang, Quan Li et al. report on thermo- and mechanochromic camouflage and self-healing in biomimetic soft actuators based on liquid crystal elastomers.

Thermo‐ and Mechanochromic Camouflage and Self‐Healing in Biomimetic Soft Actuators Based on Liquid Crystal Elastomers

AbstractIn nature, many mysterious creatures capable of deformation camouflage, color camouflage, and self‐healing have inspired scientists to develop various biomimetic soft robots. However, the systematic integration of all the above functionalities into a single soft actuator system still remains a challenge. Here we chemically introduce a multi‐stimuli‐responsive tetraarylsuccinonitrile (TASN) chromophore into a liquid crystal elastomer (LCE) network through a facile thiol‐ene photoaddition method. The obtained TASN‐LCE soft actuators not only exhibit reversible shape‐morphing and reversible color‐changing behavior in response to heat and mechanical compression, but also show excellent self‐healing, reprogramming and recycling characteristics. We hope that such a TASN‐LCE actuator system endowed with dynamic distortion, thermo‐ and mechano‐chromic camouflage, and self‐healing functionalities would pave the way for further development of multifunctional biomimetic soft robotic devices.

Thermo- and Mechanochromic Camouflage and Self-Healing in Biomimetic Soft Actuators Based on Liquid Crystal Elastomers.

In nature, many mysterious creatures capable of deformation camouflage, color camouflage, and self-healing have inspired scientists to develop various biomimetic soft robots. However, the systematic integration of all the above functionalities into a single soft actuator system still remains a challenge. Here we chemically introduce a multi-stimuli-responsive tetraarylsuccinonitrile (TASN) chromophore into a liquid crystal elastomer (LCE) network through a facile thiol-ene photoaddition method. The obtained TASN-LCE soft actuators not only exhibit reversible shape-morphing and reversible color-changing behavior in response to heat and mechanical compression, but also show excellent self-healing, reprogramming and recycling characteristics. We hope that such a TASN-LCE actuator system endowed with dynamic distortion, thermo- and mechano-chromic camouflage, and self-healing functionalities would pave the way for further development of multifunctional biomimetic soft robotic devices.

Flexible anisotropic magneto-sensitive elastomer films with out-of-plane particle chain for bionic actuator

Owing to the flexible and controllable characteristics, the magnetic composite film becomes an ideal option for future portable, efficient and multifunctional magnetic soft actuators. Here, an anisotropic magneto-sensitive elastomer film (MSEF) composite based on polydimethylsiloxane (PDMS) and high concentration of carbonyl iron particles (CIPs) was developed. The off-plane design of CIP structures endows MSEF excellent field-dependent deformability and actuation ability. The off-plane bending angle of the MSEF-30° in 87mT uniform magnetic field could reach 70.78°. Moreover, the MSEF-20° could lift a heavy object 66.4 times its own weight. The influences of particle chain orientation, CIP contents, thickness and applied magnetic field on the magneto-induced deformation behavior were fully discussed, and finite element calculations were performed to clarify the experimental results. An improved balance equation was proposed and qualitatively explained the experimental results under different magnetic fields. Based on the MSEF composite, biomimetic soft actuators with bidirectional deformation and self-sensing functions were produced respectively. The two easy preparation and programmable soft actuators could achieve the expected actuation effect, indicating that the anisotropic MSEFs have great potential as soft actuators in the fields of biomedicine, microfluidics, intelligent robots and bionics applications.

Bioinspired Ultrathin Piecewise Controllable Soft Robots

AbstractIn nature, animals or plants often use soft organs to move and hunt. Research works on bioinspired materials and devices have attracted more and more interest as which show the potential for future intelligent robots. As key components of soft robots, biomimetic soft actuators are adapted to greater requirements for convenient, accurate, and programmable controlling robots. Here, a class of materials and processing routes of ultrathin actuators are reported for bioinspired piecewise controllable soft robots, where the actuators associate with thermal‐responsible soft silicone thin film with thickness as thin as 45 µm and electrically driven by well mechanical designed metallic thin film electrodes. Multiple electrodes in the robots in charge of individual segments control allow the soft robots exhibiting similar functionalities of animals or plants (for example, imitating the tongue of a reptile, such as chameleon to hunt moving preys, and mimicking vines to tightly wind around objects). These bionic results in the soft robots demonstrate their advantages in precise and flexible operation, which provides a good reference for the future research of intelligent soft actuators and robots.

Biomimetic Hierarchically Arranged Nanofibrous Structures Resembling the Architecture and the Passive Mechanical Properties of Skeletal Muscles: A Step Forward Toward Artificial Muscle.

Skeletal muscles are considered to date the best existing actuator in nature thanks to their hierarchical multiscale fibrous structure capable to enhance their strength and contractile performances. In recent years, driven by the growing of the soft robotics and tissue-engineering research field, many biomimetic soft actuators and scaffolds were designed by taking inspiration from the biological skeletal muscle. In this work we used the electrospinning technique to develop a hierarchically arranged nanofibrous structure resembling the morphology and passive biomechanical properties of skeletal muscles. To mimic the passive properties of muscle, a low-modulus polyurethane was used. Several electrospun structures (mats, bundles, and a muscle-like assembly) were produced with different internal 3D arrangements of the nanofibers. A thermal characterization through thermogravimetric and differential scanning calorimetry analysis investigated the physico-chemical properties of the material. The multiscale morphological similarities with the biological counterpart were verified by means of scanning electron microscopy investigation. The tensile tests on the different electrospun samples revealed that the muscle-like assembly presented slightly higher strength and stiffness compared to the skeletal muscle ones. Moreover, mathematical models of the mechanical behavior of the nanofibrous structures were successfully developed, allowing to better investigate the relationships between structure and mechanics of the samples. The promising results suggest the suitability of this hierarchical electrospun nanofibrous structure for applications in regenerative medicine and, if combined with active materials, in soft actuators for robotic.

Selectively aligned cellulose nanofibers towards high-performance soft actuators

Motion of plants in response to environment stimuli (e.g., opening and closing of pinecones) often finds its origin in the organized microscopic structures of the moving part, which sheds light on a new way to design and fabricate high-performance biomimetic soft actuators. In this paper, we design a micro-patterned soft actuator consisting of a selectively aligned cellulose nanofiber layer and a passivation layer. The unique structure of the cellulose nanofiber layer is achieved by an evaporation-assisted self-assembly method (inspired by the “coffee ring” effect). Benefiting from the hydrophilic, nanoporous and well-aligned cellulose nanofiber network, the resultant soft actuator demonstrates a fast (response time less than 1s), extremely powerful (∼1000 times lifting weight ratio), and controllable response to external environmental stimuli, which is comparable to the best performing soft actuators reported in the literature. Mechanics modeling further reveals that the well-aligned cellulose nanofiber layer plays an important role in both the final curvature and generation of the actuation forces. Proof-of-concept demonstrations of the micro-patterned soft actuators as mechanical arms and soft walking robots indicate their great potential for soft robots and biomimetic systems.

Micromachining‐Compatible, Facile Fabrication of Polymer Nanocomposite Spin Crossover Actuators

Abstract[FeII(Htrz)2(trz)](BF4) spin crossover particles of 85 nm mean size are dispersed in an SU‐8 polymer matrix and spray‐coated onto silicon microcantilevers. The subsequent photothermal treatment of the polymer resist leads to micrometer thick, smooth, and homogeneous coatings, which exhibit well‐reproducible actuation upon the thermally induced spin transition. The actuation amplitude as a function of temperature is accurately determined by combining integrated piezoresistive detection with external optical interferometry, which allows for the assessment of the associated actuation force (9.4 mN), stress (28 MPa), strain (1.0%), and work density (140 mJ cm−3) through a stratified beam model. The dynamical mechanical characterization of the films evidences an increase of the resonance frequency and a concomitant decrease of the damping in the high‐temperature phase, which arises due to a combined effect of the thickness and mechanical property changes. The spray‐coating approach is also successfully extended to scale up the actuators for the centimeter range on a polymer substrate providing perspectives for biomimetic soft actuators.

1A2-R10 跳躍・走行・舞踏ロボット用バイオミメティックアクチュエータの開発 : シリコンゴム腱構造アクチュエータによる屈伸反動跳躍の実現(バイオミメティクス・バイオメカトロニクス(2))

We have been developing motor-tendon-joint series connection type biomimetic soft actuators to make robots act jumping, running and dancing like animals. We proposed and have been developing a silicone rubber compression type tendon structure for robots which act as a tendon of the muscular-skeletal system of the animals. Our first actuator using this silicone rubber tendon structure is a bit rack of motor power as a jumping robot. Therefore, in the previous paper, we newly produced a One-axis actuator using 200W coreless motor. We also modified the tendon structure. However, we could not demonstrate that the tendon structure improved the jumping height of 1 axis type actuator. Moreover, it was clarified that the knee joint angle was not controlled correctly after presenting the previous report. Therefore, in this study, we modified the tendon structure to load both tension/compression. We also introduce feedforward/feedback adding type control program to reduce vibration. The results showed that the newly made control program drastically decreased the vibration of the knee joint angle. The jumping height of the bend and stretch reaction jumping also exceeded the height of the simple jumping from full-bending position. This result showed that the modified tendon structure improved the jumping height of 1 axis actuator.

2A1-A20 跳躍・走行・舞踏ロボット用バイオミメティックアクチュエータの開発 : シリコンゴムを用いたロボット用腱構造の開発

The authers have been developing motor-spring-joint series connection type biomimetic soft actuators to make robots act jumping, runnning and dancing like animals. The spring plays the role of the tendon of the mascular-skeletal system of the animals. In this study, instead of the formerly developed actuators using normal torsion coil type spring, a silicone rubber compression type tendon structure was proposed. After the trial manufacturing, the silicone rubber tendon structure can be composed less weight with more load capacity. It also can be adjusted its rigidity easily to the same order of such as human achilles tendon. The load capacity and the rigidity of the silicone rubber tendon structure can be adjusted by the size (width and size of the cross-sectional area) and the rigidity of the silicone rubber. A single joint type biomimetic actuator was also produced using silicone rubber tendon structure and 150W D.C. coreless motor. The actuator was set on the one-axis movable test bench to restrict the motion along the spline shaft. After the simple jumping experiment, it was found that the actuator could jump to the 115mm height softly and without needless vibrations.

Load dependence of soft actuators based on polypyrrole tubes

Isotonic load stress dependence of biomimetic soft actuators based on polypyrrole tubes has been studied to elucidate the work behaviour. Polypyrrole (PPy) tubes were electrochemically prepared on gold coated acryl resin in an aqueous solution of pyrrole and dodecylbenzensulfonic acid (DBS). The tubes were operated electrochemically in aqueous 1 M LiCl, and the change of tube length was measured under various load stresses. It was found that with increasing load stresses the response time slowed down and the contraction ratio reduced. Hence, the current decreased and lasted longer, indicating that the tube was sensing the load stress. During contraction of the tube, the conversion efficiency was estimated from the electrical input and mechanical output energies to be 0.12%. The maximum volumetric work was approximately 120 kJ/m 3. The results were discussed taking the dynamics of ion migration into consideration.