Electroactive polymer (EAP) actuators—background review

Electromechanical Performances of Polyvinyl Chloride Gels Using (Polyvinyl Chloride-Co-Vinyl Acetate) (P(VC-VA)) Synergistic Plasticization

The current polyvinyl chloride (PVC) gel flexible actuators are facing challenges of high input voltage and an insufficient elastic modulus. In this study, we conducted a detailed study on the properties of PVC gel prepared by introducing the modifier polyvinyl chloride-vinyl acetate (P(VC-VA)). We compared a modified PVC gel with the traditional one in terms of the relative dielectric constant, mechanical modulus, and electromechanical actuation performance. Experimental results demonstrated that the introduction of P(VC-VA) enhanced the dielectric constant and reduced the driving electric field strength of PVC gels. The dielectric constant increased from 4.77 to 7.3. The electromechanical actuation performance increased by 150%. We employed the Gent model to fit the experimental results, and the actual experimental data aligned well with the expectations of the Gent model. The research results show that this type of plasticizing method effectively balanced the mechanical and electrical performance of PVC gels. This study summarizes the experimental results and performance analysis of PVC gels prepared using innovative plasticization methods, revealing the potential engineering applications of polymeric gels.

Body-temperature softening electronic ink for additive manufacturing of transformative bioelectronics via direct writing

Mechanically transformative electronic systems (TESs) built using gallium have emerged as an innovative class of electronics due to their ability to switch between rigid and flexible states, thus expanding the versatility of electronics. However, the challenges posed by gallium's high surface tension and low viscosity have substantially hindered manufacturability, limiting high-resolution patterning of TESs. To address this challenge, we introduce a stiffness-tunable gallium-copper composite ink capable of direct ink write printing of intricate TES circuits, offering high-resolution (~50 micrometers) patterning, high conductivity, and bidirectional soft-rigid convertibility. These features enable transformative bioelectronics with design complexity akin to traditional printed circuit boards. These TESs maintain rigidity at room temperature for easy handling but soften and conform to curvilinear tissue surfaces at body temperature, adapting to dynamic tissue deformations. The proposed ink with direct ink write printing makes TES manufacturing simple and versatile, opening possibilities in wearables, implantables, consumer electronics, and robotics.

Soft Sensors and Actuators for Wearable Human-Machine Interfaces

Haptic human-machine interfaces (HHMIs) combine tactile sensation and haptic feedback to allow humans to interact closely with machines and robots, providing immersive experiences and convenient lifestyles. Significant progress has been made in developing wearable sensors that accurately detect physical and electrophysiological stimuli with improved softness, functionality, reliability, and selectivity. In addition, soft actuating systems have been developed to provide high-quality haptic feedback by precisely controlling force, displacement, frequency, and spatial resolution. In this Review, we discuss the latest technological advances of soft sensors and actuators for the demonstration of wearable HHMIs. We particularly focus on highlighting material and structural approaches that enable desired sensing and feedback properties necessary for effective wearable HHMIs. Furthermore, promising practical applications of current HHMI technology in various areas such as the metaverse, robotics, and user-interactive devices are discussed in detail. Finally, this Review further concludes by discussing the outlook for next-generation HHMI technology.

Transparent and Flexible Actuator Based on a Hybrid Dielectric Layer of Wavy Polymer and Dielectric Fluid Mixture

Transparent and flexible vibrotactile actuators play an essential role in human-machine interaction applications by providing mechanical stimulations that can effectively convey haptic sensations. In the present study, we fabricated an electroactive, flexible, and transparent vibrotactile actuator with a dielectric layer including a dielectric elastomer and dielectric fluid mixture. The dielectric fluid mixture of propylene carbonate (PC) and acetyl tributyl citrate (ATBC) was injected to obtain a transparent dielectric layer. To further improve the haptic performance, different weight ratios of dielectric fluid (PC: ATBC) were injected. The fabricated vibrotactile actuators based on a transparent dielectric layer were investigated for their electrical and electromechanical behavior. The proposed actuators generate a large vibrational intensity (~2.5 g) in the range of 200-250 Hz. Hence, the proposed actuators open up a new class of vibrotactile actuators for possible use in various domains, including robotics, smart textiles, teleoperation, and the metaverse.

Exo Supportive Devices: Summary of Technical Aspects

Human societies have been trying to mitigate the suffering of individuals with physical impairments, with a special effort in the last century. In the 1950s, a new concept arose, finding similarities between animal exoskeletons, and with the goal of medically aiding human movement (for rehabilitation applications). There have been several studies on using exosuits with this purpose in mind. So, the current review offers a critical perspective and a detailed analysis of the steps and key decisions involved in the conception of an exoskeleton. Choices such as design aspects, base materials (structure), actuators (force and motion), energy sources (actuation), and control systems will be discussed, pointing out their advantages and disadvantages. Moreover, examples of exosuits (full-body, upper-body, and lower-body devices) will be presented and described, including their use cases and outcomes. The future of exoskeletons as possible assisted movement solutions will be discussed-pointing to the best options for rehabilitation.

Exploring stimuli-responsive elastin-like polypeptide for biomedicine and beyond: potential application as programmable soft actuators

With the emergence of soft robotics, there is a growing need to develop actuator systems that are lightweight, mechanically compliant, stimuli-responsive, and readily programmable for precise and intelligent operation. Therefore, "smart" polymeric materials that can precisely change their physicomechanical properties in response to various external stimuli (e.g., pH, temperature, electromagnetic force) are increasingly investigated. Many different types of polymers demonstrating stimuli-responsiveness and shape memory effect have been developed over the years, but their focus has been mostly placed on controlling their mechanical properties. In order to impart complexity in actuation systems, there is a concerted effort to implement additional desired functionalities. For this purpose, elastin-like polypeptide (ELP), a class of genetically-engineered thermoresponsive polypeptides that have been mostly utilized for biomedical applications, is being increasingly investigated for stimuli-responsive actuation. Herein, unique characteristics and biomedical applications of ELP, and recent progress on utilizing ELP for programmable actuation are introduced.

From Nature to Technology: Exploring Bioinspired Polymer Actuators via Electrospinning

Nature has always been a source of inspiration for the development of novel materials and devices. In particular, polymer actuators that mimic the movements and functions of natural organisms have been of great interest due to their potential applications in various fields, such as biomedical engineering, soft robotics, and energy harvesting. During recent years, the development and actuation performance of electrospun fibrous meshes with the advantages of high permeability, surface area, and easy functional modification, has received extensive attention from researchers. This review covers the recent progress in the state-of-the-art electrospun actuators based on commonly used polymers such as stimuli-sensitive hydrogels, shape-memory polymers (SMPs), and electroactive polymers. The design strategies inspired by nature such as hierarchical systems, layered structures, and responsive interfaces to enhance the performance and functionality of these actuators, including the role of biomimicry to create devices that mimic the behavior of natural organisms, are discussed. Finally, the challenges and future directions in the field, with a focus on the development of more efficient and versatile electrospun polymer actuators which can be used in a wide range of applications, are addressed. The insights gained from this review can contribute to the development of advanced and multifunctional actuators with improved performance and expanded application possibilities.

A Concise Guide to Silicone-Based Spring-Roll Actuator Assembly

A spring-roll actuator is a multilayer configuration of dielectric elastomer actuators that deforms in response to an electric field. To date, all spring-roll actuators are based on acrylate dielectric elastomers (DEs), and a few can reach deformations on a par with strains observed in natural muscles. Sensitivity to temperature and humidity, as well as the slow response times of acrylates, limit the commercialisation of these actuators. In this work, we developed a spring-roll actuator using commercial silicone DEs because they allow for a broader range of processing temperature and rapid response. Electrodes were deposited on a pre-strained DE film, coated with functional organosilicone polymer composite, and rolled around a metal spring. The coating enhanced the interfacial adhesion between DE and compliant electrodes, preserving the integrity and electro-mechanical properties of the fabricated spring-roll actuator. As to performance, the silicone-based spring-roll actuator could bear 200 times its own weight and displace it by 6% at the applied electric field of 90 V/μm.

Cellulose-Based Ionic Conductor: An Emerging Material toward Sustainable Devices

Ionic conductors (ICs) find widespread applications across different fields, such as smart electronic, ionotronic, sensor, biomedical, and energy harvesting/storage devices, and largely determine the function and performance of these devices. In the pursuit of developing ICs required for better performing and sustainable devices, cellulose appears as an attractive and promising building block due to its high abundance, renewability, striking mechanical strength, and other functional features. In this review, we provide a comprehensive summary regarding ICs fabricated from cellulose and cellulose-derived materials in terms of fundamental structural features of cellulose, the materials design and fabrication techniques for engineering, main properties and characterization, and diverse applications. Next, the potential of cellulose-based ICs to relieve the increasing concern about electronic waste within the frame of circularity and environmental sustainability and the future directions to be explored for advancing this field are discussed. Overall, we hope this review can provide a comprehensive summary and unique perspectives on the design and application of advanced cellulose-based ICs and thereby encourage the utilization of cellulosic materials toward sustainable devices.

A Proposal of Bioinspired Soft Active Hand Prosthesis

Soft robotics have broken the rigid wall of interaction between humans and robots due to their own definition and manufacturing principles, allowing robotic systems to adapt to humans and enhance or restore their capabilities. In this research we propose a dexterous bioinspired soft active hand prosthesis based in the skeletal architecture of the human hand. The design includes the imitation of the musculoskeletal components and morphology of the human hand, allowing the prosthesis to emulate the biomechanical properties of the hand, which results in better grips and a natural design. CAD models for each of the bones were developed and 3D printing was used to manufacture the skeletal structure of the prosthesis, also soft materials were used for the musculoskeletal components. A myoelectric control system was developed using a recurrent neural network (RNN) to classify the hand gestures using electromyography signals; the RNN model achieved an accuracy of 87% during real time testing. Objects with different size, texture and shape were tested to validate the grasping performance of the prosthesis, showing good adaptability, soft grasping and mechanical compliance to object of the daily life.

Design of a Fuel Explosion-Based Chameleon-Like Soft Robot Aided by the Comprehensive Dynamic Model

Soft robotics have advantages over the traditional rigid ones to achieve the bending motion but face with challenges to realize the rapid and long-distance linear motion due to the lack of a suitable actuation system. In this paper, a new explosion-based soft robot is proposed to generate the axial fast extension by the explosion pressure. To support and predict the performance of this explosion-based soft robot, a novel dynamic model is developed by considering the change of working fluid (molecular numbers) and some unavoidable and influential factors in the combustion process. Then, based on the physical prototype, a set of experiments is conducted to test the performance of the explosion-based soft robot in performing the axial extensions, as well as to validate the model proposed in this article. It is found that the novel explosion-based soft robot can achieve rapid axial extension by the developed explosion-based actuation system. The explosion-based soft robot can achieve 41-mm displacement at a fuel mass of 180 mg. In addition, the proposed dynamic model can be validated with an average error of 1.5%. The proposed approach in this study provides a promising solution for future high-power density explosion-based soft robots.

Biopolymer-based electrospun fibers in electrochemical devices: versatile platform for energy, environment, and health monitoring

Electrochemical power tools are regarded as essential keys in a world that is becoming increasingly reliant on fossil fuels in order to meet the challenges of rapidly depleting fossil fuel supplies. Additionally, due to the industrialization of societies and the growth of diseases, the need for sensitive, reliable, inexpensive, and portable sensors and biosensors for noninvasive monitoring of human health and environmental pollution is felt more than ever before. In recent decades, electrospun fibers have emerged as promising candidates for the fabrication of highly efficient electrochemical devices, such as actuators, batteries, fuel cells, supercapacitors, and biosensors. Meanwhile, the use of synthetic polymers in the fabrication of versatile electrochemical devices has raised environmental concerns, leading to an increase in the quest for natural polymers. Natural polymers are primarily derived from microorganisms and plants. Despite the challenges of processing bio-based electrospun fibers, employing natural nanofibers in the fabrication of electrochemical devices has garnered tremendous attention in recent years. Here, various natural polymers and the strategies employed to fabricate various electrospun biopolymers are briefly covered. The recent advances and research strategies used to apply the bio-based electrospun membranes in different electrochemical devices are carefully summarized, along with the scopes in various advanced technologies. A comprehensive and critical discussion about the use of biopolymer-based electrospun fibers as the potential alternative to non-renewable ones in future technologies is briefly highlighted. This review will serve as a field opening platform for using different biopolymer-based electrospun fibers to advance the electrochemical device-based renewable and sustainable technologies, which will be of high interest to a large community. Accordingly, future studies should focus on feasible and cost-effective extraction of biopolymers from natural resources as well as fabrication of high-performance nanofibrous biopolymer-based components applicable in various electrochemical devices.

QPSO-MPC based tracking algorithm for cable-driven continuum robots

Cable-driven continuum robots (CDCRs) can flexibly travel through narrow space for complex workspace tasks. However, it is challenging to design the trajectory tracking algorithm for CDCRs due to their nonlinear dynamic behaviors and cable hysteresis characteristics. In this contribution, a model predictive control (MPC) tracking algorithm based on quantum particle swarm optimization (QPSO) is designed for CDCRs to realize effective trajectory tracking under constraints. In order to make kinematic analysis of a CDCR, the forward and inverse mapping among actuation space, joint space and work space is analyzed by using the piecewise constant curvature method and the homogeneous coordinate transformation. To improve the performance of conventional MPC for complex tracking tasks, QPSO is adopted in the rolling optimization of MPC for its global optimization performance, robustness and fast convergence. Both simulation and operational experiment results demonstrate that the designed QPSO-MPC presents high control stability and trajectory tracking precision. Compared with MPC and particle swarm optimization (PSO) based MPC, the tracking error of QPSO-MPC is reduced by at least 43 and 24%, respectively.

Modeling dynamic swelling of polymer-based artificial muscles

Polymer-based artificial muscles are lightweight, are flexible, can have variable stiffness, and provide actuation in applications in which heavy actuators are not feasible. Achieving device requirements, such as strain, strain rate, lifetime, achievable work, and efficiency, requires material and muscle geometry design. This study is motivated by the possibility of significant actuation from twisted and coiled polymer (TCP) fibers that rely on radial swelling to produce reversible work. Modeling the actuation of advanced polymers is essential for defining design metrics. An analytical thermodynamic expression based on Flory-Rehner Theory was combined with a numerical transport model in order to simulate transient swelling of a polymeric network driven by diffusion and migration. Radial swelling of polymer fibers was modeled, including parametric studies and comparison to experimental data. By increasing the transport distance, swelling is shown to increase the time to equilibrium, but this can be more than compensated by applying voltage to take advantage of ion migration/electroosmotic drag. This work indicates that, in addition to migration, dimensions smaller than 100 micrometers here are needed to achieve the sub-second response times of natural muscles. The impact of polymer swelling on transport in polymers is directly evaluated by locally accounting for the length increase of discrete elements due to solvent presence, which cannot be done analytically. Furthermore, strain and work done by swelling a TCP is modelled, and the benefit of anisotropic swelling and constant modulus is quantified.

Smart Compression Therapy Devices for Treatment of Venous Leg Ulcers: A Review

Venous leg ulcers can have significant social and economic impacts, and are generally treated by applying compression to the lower limb, which aids in promoting blood return to the heart. Compression therapies commonly involve the use of passive bandages that suffer from issues associated with incorrect application, and although automated solutions have begun to appear; these are often bulky and hinder mobility. Emerging microtechnologies and new materials enable the development of "smart" compression therapy devices, which are defined as systems that use miniaturized and lightweight actuators and electronics to control the applied pressure. This paper reviews the state of the art in smart compression therapy research. A total of seventeen different devices has been identified, categorized as using one of three actuation mechanisms: pneumatic compression, motor-driven mechanisms, and smart materials (including shape memory alloys, shape memory polymers, and electroactive polymers). The field is still in its relative infancy and further refinements are required to create mass manufacturable compression dressing systems that meet medical, ergonomic, and economic standards. The use of miniaturized actuators has immense potential for the development of smart compression dressings, which will ultimately lead to higher compliance, increased patient comfort, enhanced mobility, and better treatment outcomes.

Recent Progress in Development and Applications of Ionic Polymer-Metal Composite

Electroactive polymer (EAP) is a polymer that reacts to electrical stimuli, such as voltage, and can be divided into electronic and ionic EAP by an electrical energy transfer mechanism within the polymer. The mechanism of ionic EAP is the movement of the positive ions inducing voltage change in the polymer membrane. Among the ionic EAPs, an ionic polymer-metal composite (IPMC) is composed of a metal electrode on the surface of the polymer membrane. A common material for the polymer membrane of IPMC is Nafion containing hydrogen ions, and platinum, gold, and silver are commonly used for the electrode. As a result, IPMC has advantages, such as low voltage requirements, large bending displacement, and bidirectional actuation. Manufacturing of IPMC is composed of preparing the polymer membrane and plating electrode. Preparation methods for the membrane include solution casting, hot pressing, and 3D printing. Meanwhile, electrode formation methods include electroless plating, electroplating, direct assembly process, and sputtering deposition. The manufactured IPMC is widely demonstrated in applications such as grippers, micro-pumps, biomedical, biomimetics, bending sensors, flow sensors, energy harvesters, biosensors, and humidity sensors. This paper will review the overall field of IPMC by demonstrating the categorization, principle, materials, and manufacturing method of IPMC and its applications.

Electroactive Polymer-Based Composites for Artificial Muscle-like Actuators: A Review

Unlike traditional actuators, such as piezoelectric ceramic or metallic actuators, polymer actuators are currently attracting more interest in biomedicine due to their unique properties, such as light weight, easy processing, biodegradability, fast response, large active strains, and good mechanical properties. They can be actuated under external stimuli, such as chemical (pH changes), electric, humidity, light, temperature, and magnetic field. Electroactive polymers (EAPs), called ‘artificial muscles’, can be activated by an electric stimulus, and fixed into a temporary shape. Restoring their permanent shape after the release of an electrical field, electroactive polymer is considered the most attractive actuator type because of its high suitability for prosthetics and soft robotics applications. However, robust control, modeling non-linear behavior, and scalable fabrication are considered the most critical challenges for applying the soft robotic systems in real conditions. Researchers from around the world investigate the scientific and engineering foundations of polymer actuators, especially the principles of their work, for the purpose of a better control of their capability and durability. The activation method of actuators and the realization of required mechanical properties are the main restrictions on using actuators in real applications. The latest highlights, operating principles, perspectives, and challenges of electroactive materials (EAPs) such as dielectric EAPs, ferroelectric polymers, electrostrictive graft elastomers, liquid crystal elastomers, ionic gels, and ionic polymer–metal composites are reviewed in this article.

Preparation and Modification Technology Analysis of Ionic Polymer-Metal Composites (IPMCs)

As a new type of flexible smart material, ionic polymer-metal composite (IPMC) has the advantages of being lightweight and having fast responses, good flexibility, and large deformation ranges. However, IPMC has the disadvantages of a small driving force and short lifespan. Based on this, this paper firstly analyzes the driving mechanism of IPMC. Then, it focuses on the current preparation technology of IPMC from the aspects of electroless plating and mechanical plating. The advantages and disadvantages of various preparation methods are analyzed. Due to the special driving mechanism of IPMC, there is a problem of short non-aqueous working time. Therefore, the modification research of IPMC is reviewed from the aspects of the basement membrane, working medium, and electrode materials. Finally, the current challenges and future development prospects of IPMC are discussed.

Recent advances in the 3D printing of ionic electroactive polymers and core ionomeric materials

The recent advances in the 3D printing, or additive manufacturing, of ionic electroactive polymers (EAP) and their future applications.

A Novel 3D Ring-Based Flapper Valve for Soft Robotic Applications

In this paper, the design and testing of a novel valve for the intuitive spatial control of soft or continuum manipulators are presented. The design of the valve is based on the style of a hydraulic flapper valve, but with simultaneous control of three pressure feed points, which can be used to drive three antagonistically arranged hydraulic actuators for positioning soft robots. The variable control orifices are arranged in a rotationally symmetric radial pattern to allow for an inline mounting configuration of the valve within the body of a manipulator. Positioning the valve ring at various 3D configurations results in different pressurizations of the actuators and corresponding spatial configurations of the manipulator. The design of the valve is suitable for miniaturization and use in applications with size constraints such as small soft manipulators and surgical robotics. Experimental validation showed that the performance of the valve can be reasonably modeled and can effectively drive an antagonistic arrangement of three actuators for soft manipulator control.

Accurate Electroadhesion Force Measurements of Electrostrictive Polymers: The Case of High Performance Plasticized Terpolymers

Electroadhesion is a phenomenon ruled by many characteristic intrinsic parameters. To achieve a good adhesion, efficient and durable, a particular attention must be provided to the adhesion forces between the involved parts. In addition to the size and geometry of electrodes, parameters of materials such as dielectric constant, breakdown electric field, and Young's modulus are key factors in the evaluation of electroadhesion efficiency for electrostrictive polymers and electroactive devices. By analyzing these material parameters, a method is proposed to justify the choice of polymer matrices that are fit to specific electroadhesion applications. Another purpose of this work aims to demonstrate a possibility of accurately measuring the electroadhesion force. This physical parameter has been usually estimated through equations instead, because of the complexity in setup implementation to achieve highly precise measure. Comparisons based on the parameters criterion reveal that besides the intrinsic properties of material, some other parameters relating to its physical phenomena (e.g., saturation of dipolar orientation under high electric field leads to decrease dielectric constant), or physical behavior of the system (i.e., surface roughness reduces the active electrode area) must be thoroughly considered. Experimental results pointed out that plasticized terpolymer leads boosted electroadhesion performance compared to the other counterparts, up to 100 times higher than conventional polymers. The developed materials show high potential in applications of active displacement control for electrostrictive actuation.

The Soft and High Actuation Response of Graphene Oxide/Gelatin Soft Gel

The high actuation response of soft gel from a graphene oxide/gelatin composite was prepared as an alternative material in soft robotics applications. Graphene oxide (GO) was selected as the electroresponsive (ER) particle. GO was synthesized by modifying Hummer's method at various ratios of graphite (GP) to potassium permanganate (KMnO₄). To study the effect of ER particles on electromechanical properties, GO was blended with gelatin hydrogel (GEL) at various concentrations. The electrical properties of the ER particles (GO and GP) and matrix (GEL) were measured. The capacitance (C), resistance (R), and dielectric constant of the GO/GEL composite were lower than those of the GO particles but higher than those of the GEL and GP/GEL composite at the given number of particles. The effects of external electric field strength and the distance between electrodes on the degree of bending and the dielectrophoresis force (F_d) were investigated. When the external electric field was applied, the composite bent toward electrode, because the electric field polarized the functional group of polymer molecules. Under applied 400 V/mm, the GO/GEL composite (5% w/w) showed the highest deflection angle (θ = 82.88°) and dielectrophoresis force (7.36 N). From the results, we conclude that the GO/GEL composite can be an alternative candidate material for electromechanical actuator applications.

Shape-programmable magneto-active elastomer composites for curve and biomimetic behavior imitation

A programming methodology, which can be applied to soft-magnetic-material-based magneto-active elastomers (MAEs), to catch the predefined specific objective curves is proposed in this study. The objective curves have been equally separated into a couple of segments, which will be filled by the designed MAE elements. Furthermore, the designed MAE segments with different chain angles, in which the deformation orientation of each element under applied homogeneous magnetic fields has been investigated based on the designed experimental setup, are arrayed based on the proposed programming methodology to constitute the MAE composite to catch the orientation of the objective curve. The experimental results show that based on the proposed programming methodology, the MAE composites can describe different curves, which include harmonic, tangential and arc tangential functions under applied homogeneous magnetic fields with good agreement. Furthermore, on the basis of the proposed programming methodology, the MAE composites are utilized to mimic the typical biomimetic behavior (the peeking-up behavior of snakes and the flapping behavior of birds) with smooth curvature properties, in which the dynamic procedures present continuous curves.

In-Situ Synchrotron SAXS and WAXS Investigation on the Deformation of Single and Coaxial Electrospun P(VDF-TrFE)-Based Nanofibers

Coaxial core/shell electrospun nanofibers consisting of ferroelectric P(VDF-TrFE) and relaxor ferroelectric P(VDF-TrFE-CTFE) are tailor-made with hierarchical structures to modulate their mechanical properties with respect to their constituents. Compared with two single and the other coaxial membranes prepared in the research, the core/shell-TrFE/CTFE membrane shows a more prominent mechanical anisotropy between revolving direction (RD) and cross direction (CD) associated with improved resistance to tensile stress for the crystallite phase stability and good strength-ductility balance. This is due to the better degree of core/shell-TrFE-CTFE nanofiber alignment and the crystalline/amorphous ratio. The coupling between terpolymer P(VDF-TrFE-CTFE) and copolymer P(VDF-TrFE) is responsible for phase stabilization, comparing the core/shell-TrFE/CTFE with the pristine terpolymer. Moreover, an impressive collective deformation mechanism of a two-length scale in the core/shell composite structure is found. We apply in-situ synchrotron X-ray to resolve the two-length scale simultaneously by using the small-angle X-ray scattering to characterize the nanofibers and the wide-angle X-ray diffraction to identify the phase transformations. Our findings may serve as guidelines for the fabrication of the electrospun nanofibers used as membranes-based electroactive polymers.

Monolithic processing of a layered flexible robotic actuator film for kinetic electronics

Low-invasive soft robotic techniques can potentially be used for developing next-generation body-machine interfaces. Most soft robots require complicated fabrication processes involving 3D printing and bonding/assembling. In this letter, we describe a monolithic soft microrobot fabrication process for the mass production of soft film robots with a complex structure by simple 2D processing of a robotic actuator film. The 45 µg/mm² lightweight film robot can be driven at a voltage of CMOS compatible 5 V with 0.15 mm^-1 large curvature changes; it can generate a force 5.7 times greater than its self-weight. In a durability test, actuation could be carried out over 8000 times without degradation. To further demonstrate this technique, three types of film robots with multiple degrees of freedom and a moving illuminator robot were fabricated. This technique can easily integrate various electrical circuits developed in the past to robotic systems and can be used for developing advanced wearable sensing devices; it can be called "Kinetic electronics".

Electroactive Smart Materials for Neural Tissue Regeneration

Repair in the human nervous system is a complex and intertwined process that offers significant challenges to its study and comprehension. Taking advantage of the progress in fields such as tissue engineering and regenerative medicine, the scientific community has witnessed a strong increase of biomaterial-based approaches for neural tissue regenerative therapies. Electroactive materials, increasingly being used as sensors and actuators, also find application in neurosciences due to their ability to deliver electrical signals to the cells and tissues. The use of electrical signals for repairing impaired neural tissue therefore presents an interesting and innovative approach to bridge the gap between fundamental research and clinical applications in the next few years. In this review, first a general overview of electroactive materials, their historical origin, and characteristics are presented. Then a comprehensive view of the applications of electroactive smart materials for neural tissue regeneration is presented, with particular focus on the context of spinal cord injury and brain repair. Finally, the major challenges of the field are discussed and the main challenges for the near future presented. Overall, it is concluded that electroactive smart materials play an ever-increasing role in neural tissue regeneration, appearing as potentially valuable biomaterials for regenerative purposes.

Reversible Underwater Adhesion for Soft Robotic Feet by Leveraging Electrochemically Tunable Liquid Metal Interfaces

Soft crawling robots have potential applications for surveillance, rescue, and detection in complex environments. Despite this, most existing soft crawling robots either use nonadjustable feet to passively induce asymmetry in friction to actuate or are only capable of moving on surfaces with specific designs. Thus, robots often lack the ability to move along arbitrary directions in a two-dimensional (2D) plane or in unpredictable environments such as wet surfaces. Here, leveraging the electrochemically tunable interfaces of liquid metal, we report the development of liquid metal smart feet (LMSF) that enable electrical control of friction for achieving versatile actuation of prismatic crawling robots on wet slippery surfaces. The functionality of the LMSF is examined on crawling robots with soft or rigid actuators. Parameters that affect the performance of the LMSF are investigated. The robots with the LMSF prove capable of actuating across different surfaces in various solutions. Demonstration of 2D locomotion of crawling robots along arbitrary directions validates the versatility and reliability of the LMSF, suggesting broad utility in the development of advanced soft robotic systems.

Magnetoactive Soft Drivers with Radial-Chain Iron Microparticles

Magnetoactive elastomers (MAEs), one kind of typical novel magnetoactive driver applied in the soft robotic area, have become one of the research hotspots as they can provide biologically friendly driving methods with safe, preprogrammed, and easy-to-implement properties. In this study, novel MAEs embedding soft magnetic iron microparticles with radial chains, which can be molded in one piece, achieve 3D deformation, and co-work between multiple MAEs under single homogeneous stimuli, are proposed. Then, two kinds of novel magnetoactive drivers are established based on the proposed MAEs, which can achieve the synchronous pumping behavior of heart and the extension behavior of muscle under applied homogeneous magnetic fields. The experimental data show that (1) for the pumping behavior, the maximum instantaneous flow rate and total pumping volume can reach 200.1 and 52.3 mL/min, respectively, under 120 BPM applied harmonic magnetic field with 0-300 mT amplitude; (2) the muscle extension behavior can achieve a strain of 0.925 without a loading mass and carry a load of 40 times its own weight with a pronounced dynamic movement. It should be emphasized that the behavior of the proposed magnetoactive drivers can be excited by remote homogeneous magnetic fields, and it has great application potential in biomimetic or bioinspired soft driving systems.

PVDF Ultrasonic Sensors for In-Air Applications: A Review

Polyvinylidene fluoride (PVDF), a material with ferroelectric characteristics, is still extremely topical for the manufacturing of transducers, and different examples, some of which have been actively commercialized since the 1980s, are reported in the literature. In this work, we present a review focused on the PVDF technology for the manufacturing of in-air ultrasonic transducers, which found application in medical robotics, sonar systems, and automation industry (e.g., proximity sensors and obstacle detection). The aim is to provide a comprehensive view on the development of such ultrasonic transducers, highlighting the constructive choices and the advantages/disadvantages in a thorough and concise way.

Tunable Mechanical and Electrical Properties of Coaxial Electrospun Composite Nanofibers of P(VDF-TrFE) and P(VDF-TrFE-CTFE)

The coaxial core/shell composite electrospun nanofibers consisting of relaxor ferroelectric P(VDF-TrFE-CTFE) and ferroelectric P(VDF-TrFE) polymers are successfully tailored towards superior structural, mechanical, and electrical properties over the individual polymers. The core/shell-TrFE/CTFE membrane discloses a more prominent mechanical anisotropy between the revolving direction (RD) and cross direction (CD) associated with a higher tensile modulus of 26.9 MPa and good strength-ductility balance, beneficial from a better degree of nanofiber alignment, the increased density, and C-F bonding. The interfacial coupling between the terpolymer P(VDF-TrFE-CTFE) and copolymer P(VDF-TrFE) is responsible for comparable full-frequency dielectric responses between the core/shell-TrFE/CTFE and pristine terpolymer. Moreover, an impressive piezoelectric coefficient up to 50.5 pm/V is achieved in the core/shell-TrFE/CTFE composite structure. Our findings corroborate the promising approach of coaxial electrospinning in efficiently tuning mechanical and electrical performances of the electrospun core/shell composite nanofiber membranes-based electroactive polymers (EAPs) actuators as artificial muscle implants.

Resonant vibration of a thin polymer film under optical excitation

We report on the mechanical excitation of a 220 μm thick thermoplastic film in its amorphous state by the radiation pressure of light. By modulating a low power visible laser (from 100 to 600 mW) at low frequencies (below 100 Hz), we observe a deformation of the film interfaces. The phenomenon, that is independent of the laser wavelength, is amplified at a resonant frequency and reaches 0.68 μm. The deformation is reversible and varies linearly with the optical power. Using the damped oscillator model, we show that the resonant frequency depends on the surface tension of the film. The associated free energy is then compared with the energy lost, taking into account the contribution of the damping corresponding to the imaginary part of the Young's modulus.

Synergizing microfluidics with soft robotics: A perspective on miniaturization and future directions

Soft robotics has gone through a decade of tremendous progress in advancing both fundamentals and technologies. It has also seen a wide range of applications such as surgery assistance, handling of delicate foods, and wearable assistive systems driven by its soft nature that is more human friendly than traditional hard robotics. The rapid growth of soft robotics introduces many challenges, which vary with applications. Common challenges include the availability of soft materials for realizing different functions and the precision and speed of control required for actuation. In the context of wearable systems, miniaturization appears to be an additional hurdle to be overcome in order to develop truly impactful systems with a high user acceptance. Microfluidics as a field of research has gone through more than two decades of intense and focused research resulting in many fundamental theories and practical tools that have the potentials to be applied synergistically to soft robotics toward miniaturization. This perspective aims to introduce the potential synergy between microfluidics and soft robotics as a research topic and suggest future directions that could leverage the advantages of the two fields.

Soft Underwater Robot Actuated by Shape-Memory Alloys “JellyRobcib” for Path Tracking through Fuzzy Visual Control

Recent developments in bioinspired technologies combined with the advance of intelligent and soft materials have allowed soft robots to replicate the behavior of different animal species. These devices can perform complicated tasks such as reaching or adapting in constrained and unstructured environments. This article proposes a methodology to develop a soft robot called “JellyRobcib” inspired in morphology and behavior by jellyfish, using shape-memory alloy springs as actuators (as bio-muscles). Such actuators can move the jellyfish both vertically and laterally by applying closed-loop fuzzy and visual controls. Additionally, Computer-Assisted Designs and Computational Fluid Dynamics simulations have been carried out to validate the soft robot model. The results show that the robot movements are very close to the morphological behavior of a real jellyfish regarding the curves of displacements, speeds and accelerations, after performing several experiments for autonomous movement: vertical ascent, lateral movements and trajectory tracking, obtaining an accuracy of ±1479 cm and repeatability of 0.944 for lateral movements for fuzzy visual control. Furthermore, thermal measurements were taken throughout a given path, allowing the generation of temperature gradients within the underwater environment for monitoring purposes.

Modeling of a Passive-Valve Piezoelectric Micro-Pump: A Parametric Study

Piezoelectric micro-pumps offer many applications and could provide considerable flow rates in miniature systems. This study parametrically investigates the effects of major parameters, namely the length, width and attack angle of valves, piezoelectric length, and applied voltage. The results show that these parameters significantly affect the performance of the designed micro-pump. Even though increasing the piezoelectric length and operating voltage raise the flow rate, the modification of valve dimensions is more efficient since these parameters do not rely on any external power. According to the obtained results, as the length of the working valves increases, the provided flow rate becomes larger. There is an optimum condition for the width and attack angle of the valves. This optimum width is not dependent on the flow rate. With the use of the attack angle and the length of the valves as design parameters, the studied design shows promising results.

Polymer-Based MEMS Electromagnetic Actuator for Biomedical Application: A Review

In this study, we present a comprehensive review of polymer-based microelectromechanical systems (MEMS) electromagnetic (EM) actuators and their implementation in the biomedical engineering field. The purpose of this review is to provide a comprehensive summary on the latest development of electromagnetically driven microactuators for biomedical application that is focused on the movable structure development made of polymers. The discussion does not only focus on the polymeric material part itself, but also covers the basic mechanism of the mechanical actuation, the state of the art of the membrane development and its application. In this review, a clear description about the scheme used to drive the micro-actuators, the concept of mechanical deformation of the movable magnetic membrane and its interaction with actuator system are described in detail. Some comparisons are made to scrutinize the advantages and disadvantages of electromagnetic MEMS actuator performance. The previous studies and explanations on the technology used to fabricate the polymer-based membrane component of the electromagnetically driven microactuators system are presented. The study on the materials and the synthesis method implemented during the fabrication process for the development of the actuators are also briefly described in this review. Furthermore, potential applications of polymer-based MEMS EM actuators in the biomedical field are also described. It is concluded that much progress has been made in the material development of the actuator. The technology trend has moved from the use of bulk magnetic material to using magnetic polymer composites. The future benefits of these compact flexible material employments will offer a wide range of potential implementation of polymer composites in wearable and portable biomedical device applications.

Toward Conductive Polymer-Based Soft Milli-Robots for Vacuum Applications

For the last two decades, the development of conducting polymers (CP) as artificial muscles, by materials researchers and chemists, has made establishing a reliable and repeatable synthesis of such materials possible. CP-based milli-robots were mostly unknown in soft robotics, however, today, they play a vital role in robotics and smart materials forums. Indeed, this subclass of soft robots has reached a crucial moment in their history, a moment where they can display rather interesting features, based on established foundations in terms of modeling, control, sensing, and planning in various applications. The purpose of this paper is to present the potential of conductive polymer-based soft milli-robots as high-performance devices for vacuum applications. To that end, a trilayer polypyrrole-based actuator was first used inside a scanning electron microscope (SEM), characterized for different applied voltages, over a relatively long period. Additionally, the tip positioning of the cantilever was also controlled using a closed-loop control. Furthermore, as a proof of concept for more complex soft milli-robots, an S-shaped soft milli-robot was modeled, using a hybrid model comprised of two models; a multi-physics model and a kinematic model. It was then fabricated using laser machining and finally characterized using its tip displacement. polypyrrole-based soft milli-robots proved to have tremendous potential as high-performance soft robots at the microscale for a wide range of applications, including SEM micro-manipulation as well as biomedical applications.

PEDOT-Based Conducting Polymer Actuators

Conducting polymers, particularly poly(3,4-ethylenedioxythiophene) (PEDOT) and its complex with poly(styrene sulfonate) (PEDOT:PSS), provide a promising materials platform to develop soft actuators or artificial muscles. To date, PEDOT-based actuators are available in the field of bionics, biomedicine, smart textiles, microactuators, and other functional applications. Compared to other conducting polymers, PEDOT provides higher conductivity and chemical stability, lower density and operating voltages, and the dispersion of PEDOT with PSS further enriches performances in solubility, hydrophility, processability, and flexibility, making them advantageous in actuator-based applications. However, the actuators fabricated by PEDOT-based materials are still in their infancy, with many unknowns and challenges that require more comprehensive understanding for their current and future development. This review is aimed at providing a comprehensive understanding of the actuation mechanisms, performance evaluation criteria, processing technologies and configurations, and the most recent progress of materials development and applications. Lastly, we also elaborate on future opportunities for improving and exploiting PEDOT-based actuators.