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Tardigrades are the most resilient biospecies on Earth, capable of surviving extreme conditions including high temperatures, pressures, air deprivation, and exposure to noxious chemicals and radiation. The study here undertakes biomimicry of the remarkable adaptability of tardigrades by designing biomorph soft actuators (BSAs) that can endure these harsh environments. Unlike previous tardigrade‐inspired materials, which lacked a naturalistic interaction with their surroundings, the BSAs replicate the anatomical macrostructures and the non‐monotonic environmental resilience of tardigrades, especially their ability to adapt via dehydration and rehydration. Dual‐layer hydrogel spheres are employed with embedded fluid bubbles, creating cohesive yet non‐monolithic smart BSA structures. These structures exhibit high resilience to compressive, thermal, and radiation stimuli, achieved through thermoresponsive shape morphing driven by fluid balance. Their advanced capabilities are also demonstrated, such as driving a McKibben‐type artificial muscle and rapidly regenerating themselves from a state exposed to hazardous chemicals. Such versatile actuating biomorphs hold great promise for various autonomous applications, including soft robotic operations in aqueous effluents, deserts, polar regions, and outer space. [ABSTRACT FROM AUTHOR]

The widespread adoption of dielectric elastomer actuators (DEAs) as compliant artificial muscle is on the horizon after a wide range of prototype demonstrations. The next step is to accelerate the material optimization for specific design requirements. This work proposes a data‐driven framework to predict long‐term DEA energy consumption and efficiency using measurements of initial electrical properties. DEA datasets are generated from 242 pre‐stretched single‐layer actuators and 53 multi‐layer bending actuators actuated for 30–180min. Devices are made with different elastomer and electrode materials, and tested with a novel instrument that can measure multiple aspects of DEA actuation. First, experiments are conducted to develop an empirical understanding of the electro‐mechanical energy conversion mechanism and the impact of material choices during DEA actuation. Second, data‐driven models are applied to the datasets to predict energy consumption and efficiency. Third, the potential generalization of this approach is investigated by using transfer learning strategies to predict energy efficiency at 100 min with as little as 1 min of input data. Moreover, it is found that linear regression can extend the prediction up to 180 min. Additionally, transfer learning is applied to predict energy‐related properties of multi‐layer DEAs using a small dataset. The proposed data‐driven framework can evolve into an intelligent system for accelerating new material discovery by predicting performance and providing device optimization strategies. [ABSTRACT FROM AUTHOR]

Biomimetic actuation technologies with high muscle strokes, cycle rates, and work capacities are necessary for robotic systems. We present a muscle type that operates based on changes in muscle stiffness caused by volume expansion. This muscle is created by coiling a mechanically strong braid, in which an elastomer hollow tube is adhesively attached inside. We show that the muscle reversibly contracts by 47.3% when driven by an oscillating input air pressure of 120 kilopascals at 10 Hz. It generates a maximum power density of 3.0 W/g and demonstrates a mechanical contractile efficiency of 74%. The muscle's low-pressure operation allowed for portable, thermal pneumatical actuation. Moreover, the muscle demonstrated bipolar actuation, wherein internal pressure leads to muscle length expansion if the initial muscle length is compressed and contraction if the muscle is not compressed. Modeling indicates that muscle expansion significantly alters its stiffness, which causes muscle actuation. We demonstrate the utility of BCMs for fast running and climbing robots. [ABSTRACT FROM AUTHOR]

In response to the technical challenge of sustainably powering electrostatic adsorption systems requiring voltages exceeding several thousand volts, a thin film electrostatic adsorption damper (EAD) based on triboelectric high‐voltage is proposed. The core concept of the EAD relies on utilizing the changeable electrostatic force propelled by a rotary freestanding triboelectric nanogenerator (RF‐TENG) to achieve a variable stiffness effect akin to artificial muscle. By adjusting the voltage in accordance with the electrostatic force, the variable stiffness and equivalent damping coefficient can be changed, realizing an electrically controllable damping effect. The modification of dynamic adsorption properties and equivalent damping of the EAD is successfully achieved by investigating a 1D mass‐spring‐EAD vibration system, demonstrating that the damping coefficient can be adjusted from 0.1 to 5 Ns m−1 at different RF‐TENG rotation speeds. Furthermore, the practical applicability of the EAD is validated through the design and testing of a fish‐like scale structure, a joint with variable stiffness, and a heavy‐load lifter. This triboelectric high‐voltage‐based EAD presents a novel approach to sustainable power supply for electrostatic adsorption, which holds significant potential for diverse applications such as advanced cloth defense, artificial muscle technologies, load lifting operations, etc. [ABSTRACT FROM AUTHOR]

The handling of fragile, sensitive or flexible components in assembly technology and production requires grippers that are designed for gentle handling of the objects to be gripped. Suction grippers are still a widespread standard solution for this purpose. However, rising energy prices are making pneumatic grippers, which work with a central upstream compressed air supply, increasingly unattractive. The generation of the compressed air itself, the mostly leaky transmission and the relatively inefficient vacuum generation are cost drivers that many users would like to avoid. Consequently, vacuum-based gripper means are required for industrial production, which work without externally generated compressed air. At the Fraunhofer IWU, a compressed-air-free suction pad composite has been developed that enables gripping of components with a wide variety of shapes. The underlying concept is inspired by the function of the suction arms (tentacles) of an octopus. By evacuating several small volume areas, which can be individually mechanically actuated, safe and sensitive gripping of objects is possible. For the generation of the vacuum, a piston system and a principle of an artificial muscle were developed, which is controlled based on shape memory alloys. [ABSTRACT FROM AUTHOR]

Soft crawling robots are usually driven by bulky and complex external pneumatic or hydraulic actuators. In this work, we proposed a miniaturized soft crawling caterpillar based on electrohydrodynamic (EHD) pumps. The caterpillar was mainly composed of a flexible EHD pump for providing the driving force, an artificial muscle for performing the crawling, a fluid reservoir, and several stabilizers and auxiliary feet. To achieve better crawling performances for our caterpillar, the flow rate and pressure of the EHD pump were improved by using a curved electrode design. The electrode gap, electrode overlap length, channel height, electrode thickness, and electrode pair number of the EHD pump were further optimized for better performance. Compared with the EHD pumps with conventional straight electrodes, our EHD pump showed a 50% enhancement in driving pressure and a 60% increase in flow rate. The bending capability of the artificial muscles was also characterized, showing a maximum bending angle of over 50°. Then, the crawling ability of the soft crawling caterpillar is also tested. Finally, our caterpillar owns the advantages of simple fabrication, low‐cost, fast movement speed, and small footprint, which has robust and wide potential for practical use, especially over various terrains. [ABSTRACT FROM AUTHOR]

Thermoplastic elastomer gels based on styrenic triblock copolymers have been increasingly used as dielectric elastomers, particularly due to the possibility of tailoring their properties based on their composition. However, these materials have a low relative permittivity, primarily attributed to their low dipole moment. Consequently, this characteristic poses a challenge for their application as dielectric elastomers. In this work, we aim to assess the impact of adding kraft lignin on the dielectric properties of thermoplastic elastomer gels. Additionally, we investigate the effects of kraft lignin dispersion on their viscoelastic and mechanical properties. For this purpose, we used two types of kraft lignin: acidic and alkaline (ac-KL and alk-KL). The alk-KL demonstrated higher dispersibility in the polymer, mainly attributed to the deprotonation of its structure during its production process. As a result, the dielectric elastomer with alk-KL showed a 50% increase in relative permittivity compared to the pristine polymer without compromising its mechanical and viscoelastic properties. Moreover, these samples demonstrated a greater actuation strain capability in response to an electrical stimulus. Thus, the incorporation of lignin demonstrates promise as a valuable reinforcement in the development of advanced dielectric materials, enhancing their electro-mechanical performance.

Lightweight artificial muscles with large strain and large stress output have great application prospects in robotics, rehabilitation, prosthetic, and exoskeletons. Despite the excellent performance of carbon nanotube‐based artificial muscles in recent years, their widespread use is hindered by the high manufacturing costs associated with carbon nanotubes. In this paper, the study introduces a novel approach by developing artificial muscles based on pure conductive polymer coiled yarns. This achievement is facilitated by the successful fabrication of high‐strength conductive polymer microfibers. Furthermore, the study elucidates the molecular structural changes occurring during electrochemical processes that induce a substantial radial volume expansion in the microfibers. The resultant anisotropic volume change is magnified by the coiled yarn, yielding a remarkable contractile strain exceeding 11% at a high stress of 5 MPa, equivalent to lifting loads more than 4000 times their own masses, all achieved with a low input voltage of 1 V. Additionally, these conductive polymer‐based artificial muscles exhibit hydration‐induced contraction up to 33%, with swift recovery through electrical heating, leveraging their intrinsic high conductivity. This breakthrough positions high‐performance conductive polymer microfibers as a promising cost‐effective alternative to carbon nanotubes, establishing them at the forefront of lightweight artificial muscles. [ABSTRACT FROM AUTHOR]

Highly electro‐responsive soft actuators have aroused immense attention due to their large bending deformation, fast response time, and long durability under low driving voltage. Herein we present a high‐performance ionic soft actuator using carboxylated cellulose nanofiber (CCNF), ionic liquid (IL), and polyvinyl alcohol (PVA). The proposed actuator displayed excellent actuation performances such as a large bending strain of 0.41% (peak‐to‐peak displacement of 13.6 mm), specific capacitance up to 43%, long working ability (95% maintain for 2.5 h), significantly reduced phase delay, and broad frequency bandwidth (0.1–3.0 Hz), all of which were ascribed to the strong ionic interactions of CCNF with PVA and IL. Simultaneously, bionic applications of the actuators were achieved including the active stent, bionic gripper, and bionic fingers for sliding electronic photos and human‐robot interactions. Thus, the proposed actuator provides a way for the advancement of next‐generation artificial muscles, soft robots, and human‐robot interactions. Highlights: Preparing an electro‐ionic actuator using carboxylated cellulose nanofibers.Ionic interactions and cross‐linking promoting ion transport capability.The actuator displaying excellent actuation responses and bioinspired applications. [ABSTRACT FROM AUTHOR]

The study examined the impact of various calcium salts crosslinking agents on the fatigue‐resistant actuation performance of gel‐based bionic artificial muscles (GBAMs) that exhibited directional bending deflection and generated actuation force when electrically stimulated, thereby converting electrical energy into mechanical energy. Furthermore, a comparative investigation was carried out to examine the mechanical properties, electrochemical characteristics, microstructure, material composition, and actuation lifespan of GBAMs doped with various calcium salts, which were commonly found in biological muscles. Moreover, this research paper offered a comprehensive analysis of the mechanoelectric coupling's contribution towards optimizing the fatigue‐resistant actuation performance of the GBAM. The findings indicated that the GBAM, synthesized through the cross‐linking of calcium iodide doped with a 25% volume fraction of ethanol absolute, exhibited superior mechanical properties, electrochemical characteristics, microstructure, and actuation lifespan when compared to various other calcium salts. Hence, following a comprehensive comparison, it could be deduced that the fatigue‐resistant actuation performance of the GBAM, synthesized using calcium iodide doped with a 25% volume fraction of ethanol absolute as a crosslinking agent, exhibited the highest level of effectiveness when compared to the other four calcium salts. [ABSTRACT FROM AUTHOR]

Artificial muscles actuated by negative pressure offer significant benefits over those driven by positive pressure, such as high contraction ratios and improved safety, making them a promising option for various applications. This paper studies the contraction force characteristic of a bellows-like artificial muscle actuated by negative pressure. Initially, the structure, fabrication, and working principle of the artificial muscle were introduced. Subsequently, based on the force balance method, the contraction force was decomposed as the forces acted by the difference value of the inner and the outer pressures on the end plate, and the tension force derived from the adjacent contraction unit. To reduce complexity, the contraction process was divided into three phases according to the distinct contact conditions of the contraction units: uncontacted, locally contacted, and fully contacted with crests. The deformations of the contraction units in each phase were analyzed, and the corresponding contraction forces were derived. An experiment platform was constructed to test the force by changing the dimension parameters and pressure, obtaining the output force data during isobaric contraction. Finally, a comparison of the experimental and calculated results substantiated the aptness of the theorem model. [ABSTRACT FROM AUTHOR]

Humidity-responsive fiber fabric-based artificial muscles represent a class of materials that exhibit sensitive actuation properties in response to changes in wet environments. Their motion behaviors originate from structural transformations undergone by the fiber fabric under humidity stimuli. This type of artificial muscle plays a pivotal role in various application fields, including soft robotics and smart textiles. Depending on configuration differences, the muscles are primarily categorized into four types: pure fiber, composite fiber, host-guest structure and sheath structure. This article briefly summarizes their current research status introduces the construction principles and structural characteristics of these four types of materials, and further analyzes their advantages and disadvantages in terms of performance. The analysis indicates that the pure fiber type is simple and practical, the composite fiber type exhibits superior performance, the host-guest structure type demonstrates ingenious design, and the sheath structure type is stable and reliable. On this basis, the future development trends are envisioned, highlighting the need for further research and improvement in areas such as stability, response speed, autonomous regulation capabilities, and multiple stimulus responses. This article provides scientifically meaningful references and inspirations for further research in this field. [ABSTRACT FROM AUTHOR]

Electrothermal polymer artificial muscle has drawn great attention because of its unique structure for imitating the functions of natural muscles with the external thermal stimulus. Herein, we develop a thermal responsible twisted and coiled polymer fiber-based artificial muscle. In brief, the polyethylene fibers and silver-plated nylon wire are prepared; these types of fibers are twisted causing coil nucleation and ultimately nucleation of supercoils to obtain novel parallel-stranded spiral structure of artificial muscle (PE@SPN fiber artificial muscle). The excellent electrothermal property of silver-plated nylon wire contributed to the superior performance of the actuator compared to nickel wire and copper wire. The composite yarn actuator generates contractile strokes of up to 11% under 2.5 Mpa tension and outputs 140 J/kg energy density; the composite yarn actuator can work at ambient temperature about to 50 ℃ with high contractile stroke and long-term stability. In contrast to previous fiber actuators based on PA6 fishing line and sewing thread, which are normally operated at 100 ℃, the actuator based on PE@SPN fiber artificial muscle is operated at a temperature of about 50 ℃. Meanwhile, a bionic elbow joint is designed and driven by the actuator based on polyethylene fiber. We successfully demonstrate the flexion/extension of finger by using the actuation of PE@SPN fiber artificial muscle. The results of experiments show that the promise as a soft actuator towards prosthetics, wearable robot, and power-assisted device applications. [ABSTRACT FROM AUTHOR]

In organisms, liquid as a continuum intertwines architected components (organs), including nervous, vascular, and musculoskeletal systems. In this regard, spiders exhibit remarkable embodiments where hemolymph, which infuses the animal, simultaneously enables muscle activation and exoskeleton compliance. Previous works on spider‐inspired artificial systems have focused on disentangled aspects, such as pressurization and flexible structures, yet organism‐like liquid‐mediated physical intelligence integrating control, distribution of resources, actuation, and support is still to be demonstrated. Here a spider‐leg‐inspired soft exoskeleton integrating a muscular system is shown, enabled by the contained liquid through hydration for compliance conditioning and charge transport for muscle activation. A two‐photon polymerized 0.8 mm‐diameter exoskeleton is reported that contains an electrolyte solution and is actuated via contraction of an ionic electroactive polymer muscle operated at 0–1 V. The exoskeleton features reversible bending and compliant interaction with natural entities such as anthers, spider webs, and pollen grains. The reported technology demonstrator, which functionally intertwines muscularization, vascularization, and innervation via liquid, supports the development of liquid‐enabled systems based on embodied energy and multi‐material design, particularly for bioinspired soft robotics. [ABSTRACT FROM AUTHOR]

Soft continuum robots, characterized by their dexterous and compliant nature, often face limitations due to buckling under small loads. This study explores the enhancement of axial performance in soft robots intrinsically actuated with extensile fluidic artificial muscles (EFAMs) through the incorporation of bio-inspired radial supports, or ossicles. By conducting quasi-static force response experiments under varying pressure conditions (103.4–517.1 kPa), and a modified Euler column buckling model, we demonstrate that ossicles significantly increase the robots' resistance to buckling, thereby extending their application scope in payload-carrying tasks. These findings not only underscore the effectiveness of ossicle reinforcement in improving structural robustness but also pave the way for future research to optimize soft robot design for enhanced performance. [ABSTRACT FROM AUTHOR]

Plasticized polyvinyl chloride (PVC) gel has large deformation under an applied external electrical field and high driving stability in air and is a candidate artificial muscle material for manufacturing a flexible actuator. A porous PVC gel actuator consists of a mesh positive pole, a planar negative pole, and a PVC gel core layer. The current casting method is only suitable for manufacturing simple 2D structures, and it is difficult to produce multilayer porous structures. This study investigated the feasibility of a 3D-printed carbon nanotube-doped silicone electrode for manufacturing multilayer porous PVC gel artificial muscle. Carbon nanotube-doped silicone (CNT-PDMS) composite inks were developed for printing electrode layers of PVC gel artificial muscles. The parameters for the printing plane and mesh electrodes were explored theoretically and experimentally. We produced a CNT-PDMS electrode and PVC gel via integrated printing to manufacture multilayer porous PVC artificial muscle and verified its good performance. [ABSTRACT FROM AUTHOR]

Conventional passive ankle foot orthoses (AFOs) have not seen substantial advances or functional improvements for decades, failing to meet the demands of many stakeholders, especially the pediatric population with neurological disorders. Our objective is to develop the first comfortable and unobtrusive powered AFO for children with cerebral palsy (CP), the DE-AFO. CP is the most diagnosed neuromotor disorder in the pediatric population. The standard of care for ankle control dysfunction associated with CP, however, is an unmechanized, bulky, and uncomfortable L-shaped conventional AFO. These passive orthoses constrain the ankle's motion and often cause muscle disuse atrophy, skin damage, and adverse neural adaptations. While powered orthoses could enhance natural ankle motion, their reliance on bulky, noisy, and rigid actuators like DC motors limits their acceptability. Our innovation, the DE-AFO, emerged from insights gathered during customer discovery interviews with 185 stakeholders within the AFO ecosystem as part of the NSF I-Corps program. The DE-AFO is a biomimetic robot that employs artificial muscles made from an electro-active polymer called dielectric elastomers (DEs) to assist ankle movements in the sagittal planes. It incorporates a gait phase detection controller to synchronize the artificial muscles with natural gait cycles, mimicking the function of natural ankle muscles. This device is the first of its kind to utilize lightweight, compact, soft, and silent artificial muscles that contract longitudinally, addressing traditional actuated AFOs' limitations by enhancing the orthosis's natural feel, comfort, and acceptability. In this paper, we outline our design approach and describe the three main components of the DE-AFO: the artificial muscle technology, the finite state machine (the gait phase detection system), and its mechanical structure. To verify the feasibility of our design, we theoretically calculated if DE-AFO can provide the necessary ankle moment assistance for children with CP—aligning with moments observed in typically developing children. To this end, we calculated the ankle moment deficit in a child with CP when compared with the normative moment of seven typically developing children. Our results demonstrated that the DE-AFO can provide meaningful ankle moment assistance, providing up to 69% and 100% of the required assistive force during the pre-swing phase and swing period of gait, respectively. [ABSTRACT FROM AUTHOR]

Flexible grippers require appropriate stiffness to ensure stability and efficiency in unpredictable environments. While combining materials with variable stiffness and elastomers holds significant promise in this regard, concurrently achieving actuation and stiffness modulation typically results in heightened structural complexity and responsiveness issues. In this study, a giant electrorheological dielectric elastomer (GERDE) with high dielectric and high electrorheological (ER) properties is obtained by introducing giant electrorheological particles into silicone elastomers, further substantiating the ability to functionally couple actuation and stiffness‐tuning, as well as application of a flexible gripper in mimicking emotive calligraphy. Specifically, GERDE exhibits better actuating (area strain rate of 33%) and ER performance (storage modulus increment of 1.5 MP) than existing conventional dielectric elastomer (DE) actuators (such as PDMS and VHB4910) under a low electric field. Compared to reported flexible grippers, bionic flexible grippers based on GERDE actuator have enhanced actuation, stiffness adjustment capability (i.e., stiffness is increased by 2.4 times), fast response (≈180 ms), and coupling effect, and can write Chinese calligraphy of different emotions by the same trajectory. This work provides ideas and methods for achieving the integration of actuator‐variable stiffness and emotional transmission in robots. [ABSTRACT FROM AUTHOR]

Mechanical stimulation is prevalent within organisms, and appropriate regulation of such stimulation can significantly enhance cellular functions. Consequently, the in vitro construction and simulation of mechanical stimulation have emerged as a research hotspot in biomechanics. In recent years, a class of artificial muscles named electroactive polymers (EAPs), especially ionic EAPs, have shown promising applications in biomechanics. While several techniques utilizing ionic EAPs for cell mechanical stimulation have been reported, further research is needed to advance and enhance their practical applications. Here, we prepared a microactuator array based on ionic EAP artificial muscles for cell mechanical stimulation. As a preliminary effort, we created a 5 × 5 microactuator array on a supporting membrane by employing laser cutting. We evaluated the electro-actuation performance of the microactuators through experimental testing and numerical simulations, affirming the potential use of the microactuator array for cell mechanical stimulation. The devised approach could inspire innovative design concepts in the development of miniaturized intelligent electronic devices, not only in biomechanics and biomimetics but also in other related fields. [ABSTRACT FROM AUTHOR]

This paper focuses on soft actuators that utilize fluid power to drive soft robots and describes their features and applications. First, it discusses how soft actuators function as elemental technology in robots. This is followed by an introduction to the driving principle and features of fluid-driven soft actuators. It also classifies these soft actuators based on the fluid power source and the active mode of operation. Furthermore, an overview is provided on the materials employed in soft actuators and the control and evaluation methods for them. Finally, currently reported applications of these soft actuators, such as wearable devices, grippers, and bio-inspired robots, are presented. [ABSTRACT FROM AUTHOR]

Wearable mechatronics for powered orthoses, exoskeletons and prostheses require improved soft actuation systems acting as 'artificial muscles' that are capable of large strains, high stresses, fast response and self-sensing and that show electrically safe operation, low specific weight and large compliance. Among the diversity of soft actuation technologies under investigation, pneumatic devices have been the focus, during the last couple of decades, of renewed interest as an intrinsically soft artificial muscle technology, due to technological advances stimulated by applications in soft robotics. As of today, quite a few solutions are available to endow a pneumatic soft device with linear actuation and self-sensing ability, while also easily achieving these features with off-the-shelf materials and low-cost fabrication processes. Here, we describe a simple process to make self-sensing pneumatic actuators, which may be used as 'inverse artificial muscles', as, upon pressurisation, they elongate instead of contracting. They are made of an elastomeric tube surrounded by a plastic coil, which constrains radial expansions. As a novelty relative to the state of the art, the self-sensing ability was obtained with a piezoresistive stretch sensor shaped as a conductive elastomeric body along the tube's central axis. Moreover, we detail, also by means of video clips, a step-by-step manufacturing process, which uses off-the-shelf materials and simple procedures, so as to facilitate reproducibility. [ABSTRACT FROM AUTHOR]

Air cylinders are actuators that slide a piston inside cylinders by applying air pressure. We propose an air-cylinder-type artificial muscle that can be flexibly bent by using a flexible tube for the cylindrical part. The actuator output was a string connected to a piston. When the air-cylinder-type artificial muscle bends, the inner wall of the tube and the string come into contact, causing output fluctuations owing to friction. In this study, we investigated the output when an artificial muscle was bent. After describing the structure of the air-cylinder-type artificial muscle, the measurement results of the resistance force at each part of the actuator are presented. A theoretical output inspired by the capstan equation was derived, and its validity was verified by comparison with experimental results. [ABSTRACT FROM AUTHOR]

Loss of an upper limb exerts a negative influence on an individual's ability to perform their activities of daily living (ADLs), reducing quality of life and self-esteem. A prosthesis capable of performing basic ADLs functions has the capability of restoring independence and autonomy to amputees. However, current technologies present in robotic prostheses are based on rigid actuators with several drawbacks, such as high weight and low compliance. Recent advances in robotics have allowed for the development of flexible actuators and artificial muscles to overcome the limitations of rigid actuators. Dielectric elastomer actuators (DEAs) consist of a thin elastomer membrane arranged between two compliant electrodes capable of changing dimensions when stimulated with an electrical potential difference. In this work, we present the design and testing of a finger prosthesis driven by two DEAs arranged as agonist–antagonist pairs as artificial muscles. The soft actuators are designed as fiber-constrained dielectric elastomers (FCDE), enabling displacement in just one direction as natural muscles. The finger prosthesis was designed and modeled to show bend movement using just one pair of DEAs and was made of PLA in an FDM 3D printer to be lightweight. The experimental results show great agreement with the proposed model and indicate that the proposed finger prosthesis is promising in overcoming the limitations of the current rigid based actuators. [ABSTRACT FROM AUTHOR]

Soft pneumatic artificial muscles are a well actuation scheme in soft robotics due to its key features for robotic machines being safe, lightweight, and conformable. In this work, we present a versatile vacuum-powered artificial muscle (VPAM) with manually tunable output motion. We developed an artificial muscle that consists of a stack of air chambers that can use replaceable external reinforcements. Different modes of operation are achieved by assembling different reinforcements that constrain the output motion of the actuator during actuation. We designed replaceable external reinforcements to produce single motions such as twisting, bending, shearing and rotary. We then conducted a deformation and lifting force characterization for these motions. We demonstrated sophisticated motions and reusability of the artificial muscle in two soft machines with different modes of locomotion. Our results show that our VPAM is reusable and versatile producing a variety and sophisticated output motions if needed. This key feature specially benefits unpredicted workspaces that require a soft actuator that can be adjusted for other tasks. Our scheme has the potential to offer new strategies for locomotion in machines for underwater or terrestrial operation, and wearable devices with different modes of operation. [ABSTRACT FROM AUTHOR]

Self‐healable electroactive carboxymethyl cellulose/polythiophene/acid hydrolyzed cellulose (CMC/PTh/AHC) hydrogels were successfully fabricated. AHC particles dispersed well in the CMC matrix improving hydrogels thermal stability. The electro‐responsive performance of the hydrogels was investigated with respect to bending angle and bending sensitivity. The results showed that under an applied electric field, the CMC/PTh/AHC hydrogels bend toward a cathode electrode. In addition, the electroactive performance of the hydrogels decreased with increased AHC content. The CMC/PTh/AHC10 (10 wt.% AHC) hydrogel exhibited the shortest induction time (τind) of 3.35 ± 0.56 s. For self‐healing, it was found that the hydrogel with addition of 2 wt.% AHC had the highest self‐healing efficiency on both tensile strength and elongation at break (93.37 ± 3.17% and 99.35 ± 12.11%, respectively). While the self‐healing efficiency on bending angle was 82.73 ± 14.55%. The results demonstrated that the properties of the CMC/PTh/AHC2 hydrogel were close to its original properties after healing for 24 h. The results demonstrated that the CMC/PTh/AHC hydrogel can be utilized as an actuator or artificial muscle using electrical stimulus. [ABSTRACT FROM AUTHOR]

Inspired by the natural skeletal muscles, this paper presents a novel shape memory alloy-based artificial muscle matrix (AMM) with advantages of a large output force and displacement, flexibility, and compactness. According to the composition of the AMM, we propose a matrix control strategy to achieve independent control of the output force and displacement of the AMM. Based on the kinematics simulation and experiments, we obtained the output displacement and bearing capacity of the smart digital structure (SDS) and confirmed the effectiveness of the matrix control strategy to achieve force and displacement output independently and controllably. A bionic mechanical ankle actuated by AMM was proposed to demonstrate the actuating capability of the AMM. Experimental results show that the angle and force of the bionic mechanical ankle are output independently and have a significant gradient. In addition, by using a self-sensing method (resistance self-feedback) and PD control strategy, the output angle and force of the bionic mechanical ankle can be maintained for a long time without overheating of the AMM. [ABSTRACT FROM AUTHOR]

Soft pneumatic biomimetic robotic systems excel at the specific application they are designed for, often to interact or navigate unstructured environments safely. However, redeployment to new purposes requires substantial resources, from redesign to revalidation. Despite most pneumatic artificial muscles surpassing the power and contraction performance of natural muscles, natural muscles largely remain unmatched in terms of their versatility and complex performance. This is likely due to artificial muscle's low effective strain and high radial expansion, limiting parallel operating efficiencies. To address these challenges, a class of compact versatile pneumatic actuators, called multilayer artificial muscle (MAM), that are capable of deployment to different applications through configurable modularity, is presented. The MAMs are biomimetically inspired by the sarcomere, the building block for natural muscle architecture. Similarly, MAM can extend and contract as well as be rearranged to mimic muscle‐like actions and functions, such as a caterpillar locomotion robot and an entire robotic arm. The MAMs are fabricated through multilayer, multimaterial, low‐cost additive manufacturing, which offers certain advantages such as higher extension, contraction force, and durability. MAMs have the potential to provide a crucial fundamental building block toward future versatile reconfigurable architecture. [ABSTRACT FROM AUTHOR]

Soft continuum robots, characterized by their dexterous and compliant nature, often face limitations due to buckling under small loads. This study explores the enhancement of axial performance in soft robots intrinsically actuated with extensile fluidic artificial muscles (EFAMs) through the incorporation of bio-inspired radial supports, or ossicles. By conducting quasi-static force response experiments under varying pressure conditions (103.4–517.1 kPa), and a modified Euler column buckling model, we demonstrate that ossicles significantly increase the robots’ resistance to buckling, thereby extending their application scope in payload-carrying tasks. These findings not only underscore the effectiveness of ossicle reinforcement in improving structural robustness but also pave the way for future research to optimize soft robot design for enhanced performance.

Plasticized polyvinyl chloride (PVC) gel has large deformation under an applied external electrical field and high driving stability in air and is a candidate artificial muscle material for manufacturing a flexible actuator. A porous PVC gel actuator consists of a mesh positive pole, a planar negative pole, and a PVC gel core layer. The current casting method is only suitable for manufacturing simple 2D structures, and it is difficult to produce multilayer porous structures. This study investigated the feasibility of a 3D-printed carbon nanotube-doped silicone electrode for manufacturing multilayer porous PVC gel artificial muscle. Carbon nanotube-doped silicone (CNT-PDMS) composite inks were developed for printing electrode layers of PVC gel artificial muscles. The parameters for the printing plane and mesh electrodes were explored theoretically and experimentally. We produced a CNT-PDMS electrode and PVC gel via integrated printing to manufacture multilayer porous PVC artificial muscle and verified its good performance.

Conventional passive ankle foot orthoses (AFOs) have not seen substantial advances or functional improvements for decades, failing to meet the demands of many stakeholders, especially the pediatric population with neurological disorders. Our objective is to develop the first comfortable and unobtrusive powered AFO for children with cerebral palsy (CP), the DE-AFO. CP is the most diagnosed neuromotor disorder in the pediatric population. The standard of care for ankle control dysfunction associated with CP, however, is an unmechanized, bulky, and uncomfortable L-shaped conventional AFO. These passive orthoses constrain the ankle’s motion and often cause muscle disuse atrophy, skin damage, and adverse neural adaptations. While powered orthoses could enhance natural ankle motion, their reliance on bulky, noisy, and rigid actuators like DC motors limits their acceptability. Our innovation, the DE-AFO, emerged from insights gathered during customer discovery interviews with 185 stakeholders within the AFO ecosystem as part of the NSF I-Corps program. The DE-AFO is a biomimetic robot that employs artificial muscles made from an electro-active polymer called dielectric elastomers (DEs) to assist ankle movements in the sagittal planes. It incorporates a gait phase detection controller to synchronize the artificial muscles with natural gait cycles, mimicking the function of natural ankle muscles. This device is the first of its kind to utilize lightweight, compact, soft, and silent artificial muscles that contract longitudinally, addressing traditional actuated AFOs’ limitations by enhancing the orthosis’s natural feel, comfort, and acceptability. In this paper, we outline our design approach and describe the three main components of the DE-AFO: the artificial muscle technology, the finite state machine (the gait phase detection system), and its mechanical structure. To verify the feasibility of our design, we theoretically calculated if DE-AFO can provide the necessary ankle moment assistance for children with CP—aligning with moments observed in typically developing children. To this end, we calculated the ankle moment deficit in a child with CP when compared with the normative moment of seven typically developing children. Our results demonstrated that the DE-AFO can provide meaningful ankle moment assistance, providing up to 69% and 100% of the required assistive force during the pre-swing phase and swing period of gait, respectively.

Soft pneumatic artificial muscles are a well actuation scheme in soft robotics due to its key features for robotic machines being safe, lightweight, and conformable. In this work, we present a versatile vacuum-powered artificial muscle (VPAM) with manually tunable output motion. We developed an artificial muscle that consists of a stack of air chambers that can use replaceable external reinforcements. Different modes of operation are achieved by assembling different reinforcements that constrain the output motion of the actuator during actuation. We designed replaceable external reinforcements to produce single motions such as twisting, bending, shearing and rotary. We then conducted a deformation and lifting force characterization for these motions. We demonstrated sophisticated motions and reusability of the artificial muscle in two soft machines with different modes of locomotion. Our results show that our VPAM is reusable and versatile producing a variety and sophisticated output motions if needed. This key feature specially benefits unpredicted workspaces that require a soft actuator that can be adjusted for other tasks. Our scheme has the potential to offer new strategies for locomotion in machines for underwater or terrestrial operation, and wearable devices with different modes of operation.

Soft pneumatic biomimetic robotic systems excel at the specific application they are designed for, often to interact or navigate unstructured environments safely. However, redeployment to new purposes requires substantial resources, from redesign to revalidation. Despite most pneumatic artificial muscles surpassing the power and contraction performance of natural muscles, natural muscles largely remain unmatched in terms of their versatility and complex performance. This is likely due to artificial muscle's low effective strain and high radial expansion, limiting parallel operating efficiencies. To address these challenges, a class of compact versatile pneumatic actuators, called multilayer artificial muscle (MAM), that are capable of deployment to different applications through configurable modularity, is presented. The MAMs are biomimetically inspired by the sarcomere, the building block for natural muscle architecture. Similarly, MAM can extend and contract as well as be rearranged to mimic muscle‐like actions and functions, such as a caterpillar locomotion robot and an entire robotic arm. The MAMs are fabricated through multilayer, multimaterial, low‐cost additive manufacturing, which offers certain advantages such as higher extension, contraction force, and durability. MAMs have the potential to provide a crucial fundamental building block toward future versatile reconfigurable architecture.

Dielectric elastomer actuators (DEAs) offer robust, high-energy-density solutions for soft robotics. The proposed end effector consists of three spring roll configuration DEAs, each acting as a robotic finger, using a 3M VHB-F9473PC adhesive membrane. Spring roll DEAs can be designed to achieve highly specialised actuations depending on the electrode patterning and structural supports. This allows a spring roll DEA-based soft end effector to be tailor-made by simply altering the electrode patterning. The lateral force, bending angle and response time of the actuator are measured experimentally and compared with the predictions of an analytical model. The cylindrical actuator measures 70 mm in length and 15 mm in diameter and achieves a lateral force of 30 mN, a bending angle of 6.8° and a response time of ≈ 1 s. Spring roll configuration DEAs are shown to reduce the effects of viscoelasticity seen in the membrane, making the actuator more controllable at higher voltages. The dielectric constant of the membrane is shown to be a limiting factor of actuation, with a decrease in dielectric constant resulting in larger actuation. The end effector successfully grips numerous light objects for extended periods, showing the applicability of spring roll DEAs for soft end effectors. [ABSTRACT FROM AUTHOR]

Designing soft robots that are able to perceive unstructured, dynamic environments and their deformations has been a long-term goal. Previously reported self-sensing soft actuators were mostly constructed via integrating separate actuators and sensors. The actuation performances and the sensing reliability are affected owing to the unmatched materials and weak connections. Realizing a seamless integration of soft actuators and sensors remains a grand challenge. Here, we report a fabrication strategy to endow soft actuators with sensing capability and programmable actuation performances. The foam inside the actuator functions as actuator and sensor simultaneously, effectively addressing the conformability and connection reliability issues that existed in current self-sensing actuators. The actuators are lightweight (a decrease of 58% in weight), powerful (lifting a load of 433 times of its own weight), and versatile (coupling twisting and contraction motions). Furthermore, the actuators are able to detect multiple physical stimuli with high reliability, demonstrating their exteroception and proprioception capability. Two self-sensing soft robotic prototypes, including a bionic bicep and a bionic neck, are constructed to illustrate their multifunctionality. Our study opens up new possibilities for the design of soft actuators and has promising potential in a variety of applications, ranging from human-robot interaction, soft orthotics, to wearable robotics. [ABSTRACT FROM AUTHOR]

Work-related musculoskeletal disorders (WMSDs) are often caused by repetitive lifting, making them a significant concern in occupational health. Although wearable assist devices have become the norm for mitigating the risk of back pain, most spinal assist devices still possess a partially rigid structure that impacts the user's comfort and flexibility. This paper addresses this issue by presenting a smart textile-actuated spine assistance robotic exosuit (SARE), which can conform to the back seamlessly without impeding the user's movement and is incredibly lightweight. To detect strain on the spine and to control the smart textile automatically, a soft knitting sensor that utilizes fluid pressure as a sensing element is used. Based on the soft knitting hydraulic sensor, the robotic exosuit can also feature the ability of monitoring and rectifying human posture. The SARE is validated experimentally with human subjects (N = 4). Through wearing the SARE in stoop lifting, the peak electromyography (EMG) signals of the lumbar erector spinae are reduced by 22.8% ± 12 for lifting 5 kg weights and 27.1% ± 14 in empty-handed conditions. Moreover, the integrated EMG decreased by 34.7% ± 11.8 for lifting 5 kg weights and 36% ± 13.3 in empty-handed conditions. In summary, the artificial muscle wearable device represents an anatomical solution to reduce the risk of muscle strain, metabolic energy cost and back pain associated with repetitive lifting tasks. [ABSTRACT FROM AUTHOR]

Soft robots have gained significant attention in recent years owing to their high safety in human–machine interactions and exceptional adaptability to unpredictable environments. Despite great advances, achieving continuous rotation with tunable stepping angle in soft robots remains a challenge. Herein, inspired by the stepping rotation strategy of the flagellum, an artificial soft rotary motor capable of bidirectional continuous rotation and tunable stepping angles is presented. The motor features a wide range of stepping angles (−72.5° to 73.4°), enabling it to rotate to any angle position with high resolution. The soft motor also exhibits high rotation speed (18.23 r min−1), zero‐energy position‐holding, and excellent durability. Furthermore, the potential applications of the soft rotary motors, including tuning the grasping direction of a soft gripper and adjusting the winding direction of a soft tentacle is demonstrated. This work offers a universal soft fluidic component for soft robots, endowing them with enhanced agility and movement capabilities. [ABSTRACT FROM AUTHOR]

Purpose: Fetoscopic laser coagulation for twin-to-twin transfusion syndrome is challenging for anterior placenta due to the rigidity of current tools. The capacity to keep entry port forces minimal is critical for this procedure, as is optimal coagulation distance and orientation. This work introduces technological tools to this end. Methods: A novel fetoscope is presented with a rigid shaft and a flexible steerable segment at the distal end. The steerable segment can bend up to 90 ∘ even when loaded with a laser fiber. An artificial pneumatic muscle makes such acute bending possible while allowing for a low-weight and disposable device. Results: The flexible fetoscope was validated in a custom-made phantom model to measure visual range and coagulation efficacy. The flexible fetoscope shows promising results when compared to a clinical rigid curved fetoscope to reach anterior targets. The new fetoscope was then evaluated in vivo (pregnant ewe) where it successfully coagulated placental vasculature. Conclusion: The flexible fetoscope improved the ability to achieve optimal coagulation angle and distance on anteriorly located targets. The fetoscope also showed the potential to lead fetoscopic laser coagulation and other fetal surgical procedures toward safer and more effective interventions. [ABSTRACT FROM AUTHOR]

Mechanical stimulation is prevalent within organisms, and appropriate regulation of such stimulation can significantly enhance cellular functions. Consequently, the in vitro construction and simulation of mechanical stimulation have emerged as a research hotspot in biomechanics. In recent years, a class of artificial muscles named electroactive polymers (EAPs), especially ionic EAPs, have shown promising applications in biomechanics. While several techniques utilizing ionic EAPs for cell mechanical stimulation have been reported, further research is needed to advance and enhance their practical applications. Here, we prepared a microactuator array based on ionic EAP artificial muscles for cell mechanical stimulation. As a preliminary effort, we created a 5 × 5 microactuator array on a supporting membrane by employing laser cutting. We evaluated the electro-actuation performance of the microactuators through experimental testing and numerical simulations, affirming the potential use of the microactuator array for cell mechanical stimulation. The devised approach could inspire innovative design concepts in the development of miniaturized intelligent electronic devices, not only in biomechanics and biomimetics but also in other related fields.

Wearable mechatronics for powered orthoses, exoskeletons and prostheses require improved soft actuation systems acting as ‘artificial muscles’ that are capable of large strains, high stresses, fast response and self-sensing and that show electrically safe operation, low specific weight and large compliance. Among the diversity of soft actuation technologies under investigation, pneumatic devices have been the focus, during the last couple of decades, of renewed interest as an intrinsically soft artificial muscle technology, due to technological advances stimulated by applications in soft robotics. As of today, quite a few solutions are available to endow a pneumatic soft device with linear actuation and self-sensing ability, while also easily achieving these features with off-the-shelf materials and low-cost fabrication processes. Here, we describe a simple process to make self-sensing pneumatic actuators, which may be used as ‘inverse artificial muscles’, as, upon pressurisation, they elongate instead of contracting. They are made of an elastomeric tube surrounded by a plastic coil, which constrains radial expansions. As a novelty relative to the state of the art, the self-sensing ability was obtained with a piezoresistive stretch sensor shaped as a conductive elastomeric body along the tube’s central axis. Moreover, we detail, also by means of video clips, a step-by-step manufacturing process, which uses off-the-shelf materials and simple procedures, so as to facilitate reproducibility.

Vertebrates achieve a high degree of flexibility and skillful performance via a musculoskeletal system consisting of multiple joints. These joints are simultaneously driven by some multi-articular muscles, which run over two or more joints and synchronize the musculoskeletal system. However, when multi-articular muscles contract, buckling may occur in the system if each joint is not adequately supported, such as by monoarticular muscles or intervertebral discs, and we previously investigated the stability conditions for avoiding such buckling by calculating the potential energy of the muscle elasticity. Although in our previous work we considered only the muscles themselves, actual animal muscles are surrounded and constrained by fascia, other muscles, and skin, which may also influence the stability of the musculoskeletal system. Based on this characteristic, in this study, we examined the effect of the surrounding elastic elements that constrain the muscle pathway on the stability of the musculoskeletal system. We analyzed the static stability of the system with respect to potential energy using a muscle path restraint model of the serial link mechanism driven by McKibben-type pneumatic artificial muscles. Moreover, we confirmed the analytical result by conducting an experiment using a six-joint serial link robot driven by antagonistically arranged pneumatic artificial muscles. The results revealed that the restraint of the muscle path influences the stability of the system, and that the support of each joint and restraint is critical for the stability of the system.

Conventional robotic systems are built with rigid materials to deal with large forces and predetermined processes. Soft robotics, however, is an emerging field seeking to develop adaptable robots that can perform tasks in unpredictable environments and biocompatible devices that close the gap between humans and machines. Dielectric elastomers (DEs) have emerged as a soft actuation technology that imitates the properties and performance of natural muscles, making them an attractive material choice for soft robotics. However, conventional DE materials suffer from electromechanical instability (EMI), which reduces their performance and limits their applications in soft robotics. This review discusses key innovations in DE artificial muscles from a material standpoint, followed by a survey on their representative demonstrations of soft robotics. Specifically, we introduce modifications of DE materials that enable large strains, fast responses, and high energy densities by suppressing EMI. Additionally, we examine materials that allow variable stiffness and self‐healing abilities in DE actuators. Finally, we review dielectric elastomer actuator (DEA) applications in soft robotics in four categories, including automation, manipulation, locomotion, and human interaction. [ABSTRACT FROM AUTHOR]