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Actuators based on moisture-sorption-responsive materials can convert moisture energy into mechanical/electrical energy, making the development of moisture-sorption materials a promising pathway for harnessing green energy to address the ongoing global energy crisis. The deformability of these materials plays a crucial role in the overall energy conversion performance, where moisture sorption capacity determines the energy density. Efforts to boost the moisture absorption capacity and rate have led to the development of a variety of moisture-responsive materials in recent years. These materials interact with water molecules in different manners and have shown diverse application scenarios. Here, in this review, we summarize the recent progress on moisture-sorption-responsive materials and their applications. We begin by categorizing moisture-sorption materials—biomaterials, polymers, nanomaterials, and crystalline materials—according to their interaction modes with water. We then review the correlation between moisture-sorption and energy harvesting performance. Afterwards, we provide examples of the typical applications using these moisture-sorption materials. Finally, we explore future research directions aimed at developing next-generation high-performance moisture-sorption materials with higher water uptake, tunable water affinity, and faster water absorption. [ABSTRACT FROM AUTHOR]

This review systematically explores the inherent structural advantages of fiber over conventional film or bulk forms for artificial muscles, emphasizing their enhanced mechanical properties and actuation, scalability, and design flexibility. Distinctive merits of electrically powered artificial muscle fiber actuation mechanisms, including electrothermal, electrochemical and dielectric actuation, are highlighted, particularly for their operational efficiency, precise control capabilities, miniaturizability and seamless integration with electronic components. A comprehensive overview of significant research driving performance enhancements in artificial muscle fibers through materials and structural innovations is provided, alongside a discussion of the diverse design methodologies that have emerged in this field. A detailed comparative assessment evaluates the performance metrics, advantages and manufacturing complexities of each actuation mechanism, underscoring their suitability for various applications. Concluding with a strategic outlook, the review identifies key challenges and proposes targeted research directions to advance and refine artificial muscle fiber technologies. [ABSTRACT FROM AUTHOR]

Owing to the intrinsic excellent mechanical, electrical, and thermal properties of carbon nanotubes (CNTs), carbon nanotube fibers (CNTFs) have been expected to become promising candidates for the next-generation of high-performance fibers. They have received considerable interest for cutting-edge applications, such as ultra-light electric wire, aerospace craft, military equipment, and space elevators. Wet-spinning is a broadly utilized commercial technique for high-performance fiber manufacturing. Thus, compared with array spinning from drawable CNTs vertical array and direct dry spinning from floating catalyst chemical vapor deposition (FCCVD), the wet-spinning technique is considered to be a promising strategy to realize the production of CNTFs on a large scale. In this tutorial review, we begin with a summative description of CNTFs wet-spinning process. Then, we discuss the high-concentration CNTs wet-spinning dope preparation strategies and corresponding non-covalent adsorption/charge transfer mechanisms. The filament solidification during the coagulation process is another critical procedure for determining the configurations and properties for derived CNTFs. Next, we discuss post-treatment, including continuous drafting and thermal annealing, to further optimize the CNTs orientation and compact configuration. Finally, we summarize the physical property-structure relationship to give insights for further performance promotion in order to satisfy the prerequisite for detailed application. Insights into propelling high-performance CNTFs production from lab-scale to industry-scale are proposed, in anticipation of this novel fiber having an impact on our lives in the near future. [ABSTRACT FROM AUTHOR]

Inflammation is associated with an increased risk of developing various cancers in both animals and humans, primarily solid tumors but also myeloproliferative neoplasms (MPNs), myelodysplastic syndromes (MDS), and acute myeloid leukemia (AML). Multi-walled carbon nanotubes (MWCNTs), a type of carbon nanotubes (CNTs) increasingly used in medical research and other fields, are leading to a rising human exposure. Our study demonstrated that exposing mice to MWCNTs accelerated the progression of spontaneous MOL4070LTR virus-induced leukemia. Additionally, similar exposures elevated pro-inflammatory cytokines such as interleukin (IL)-1β, IL-6, and tumor necrosis factor (TNF)-α and induced reactive oxygen species (ROS) in a murine macrophage cell line. These effects were significantly reduced in immunodeficient mice and when mice were treated with methoxypolyethylene glycol amine (PEG)-modified MWCNTs. These findings underscore the necessity of evaluating the safety of MWCNTs, particularly for those with hematologic cancers. [ABSTRACT FROM AUTHOR]

Carbon nanotubes (CNTs) are considered an advanced form of carbon. They have superior characteristics in terms of mechanical and thermal properties compared to other available fibers and can be used in various applications, such as supercapacitors, sensors, and artificial muscles. The properties of single-walled carbon nanotubes (SWNTs) are significantly affected by geometric parameters such as chirality and aspect ratio, and testing conditions such as temperature and strain rate. In this study, the effects of geometric parameters and temperature on the mechanical properties of SWNTs were studied by molecular dynamics (MD) simulations using the Large-scaled Atomic/Molecular Massively Parallel Simulator (LAMMPS). Based on the second-generation reactive empirical bond order (REBO) potential, SWNTs of different diameters were tested in tension and compression under different strain rates and temperatures to understand their effects on the mechanical behavior of SWNTs. It was observed that the Young's modulus and the tensile strength decreases with increasing SWNT tube diameter. As the chiral angle increases, the tensile strength increases, while the Young's modulus decreases. The simulations were repeated at different temperatures of 300 K, 900 K, 1500 K, 2100 K and different strain rates of 1 × 10−3/ps, 0.75 × 10−3/ps, 0.5 × 10−3/ps, and 0.25 × 10−3/ps to investigate the effects of temperature and strain rate, respectively. The results show that the ultimate tensile strength of SWNTs increases with increasing strain rate. It is also seen that when SWNTs were stretched at higher temperatures, they failed at lower stresses and strains. The compressive behavior results indicate that SWNTs tend to buckle under lower stresses and strains than those under tensile stress. The simulation results were validated by and consistent with previous studies. The presented approach can be applied to investigate the properties of other advanced materials. [ABSTRACT FROM AUTHOR]

In recent years, the field of microrobots has exploded, yielding many exciting new functions and applications, from object grasping and release to in vivo drug transport. Smart responsive materials have had a profound impact on the field of microrobots and have given them unique functions and structures. We analyze three aspects of microrobots, in which the future development of microrobots requires more efforts to be invested, and in which smart materials play a significant role in the development of microrobots. These three aspects are smart materials for building microrobots, manufacturing methods, and the functions and applications they achieve. In this review, we discuss the deformation mechanism of materials in response to external stimuli, starting from smart materials, and discuss fabrication methods to realize microrobots, laying the theoretical foundation for future smart material-based microrobots to realize their intelligence and programmability. [ABSTRACT FROM AUTHOR]

Small robots for drug transportation, environmental detection and military reconnaissance have been a popular research topic in the field of robotics. Recently, people have proposed using light-driven actuators to make flexible and remote-controllable small robots. Herein, we reviewed the research on light-driven soft robots in recent years. First, we summarized and compared the performance and fabrication method of light-driven actuators. Then, we classified and summarized the structures of robots according to their move mode. After that, we described how to control the robot. Finally, the challenges of light-driven robots are discussed. [ABSTRACT FROM AUTHOR]

A Dielectric Elastomer Actuator (DEA) consists of electrodes with a dielectric layer between them. By controlling the design of the electrodes, voltage, and frequency, the operating range and speed of the DEA can be adjusted. These DEAs find applications in biomimetic robots, artificial muscles, and similar fields. When voltage is applied to the DEA, the dielectric layer undergoes compression and expansion due to electrostatic forces, which can lead to electrical breakdown. This phenomenon is closely related to the performance and lifespan of the DEA. To enhance stability and improve dielectric properties, a DEA Reservoir layer is introduced. Here, stability refers to the ability of the DEA to perform its functions even as the applied voltage increases. The Reservoir layer delays electrical breakdown and enhances stability due to its enhanced thickness. The proposed DEA in this paper is composed of a Reservoir layer and electrode layer. The Reservoir layer is placed between the electrode layers and is independently configured, not subjected to applied voltage like the electrode layers. The performance of the DEA was evaluated by varying the number of polymer layers in the Reservoir and electrode designs. Introducing the Reservoir layer improved the dielectric properties of the DEA and delayed electrical breakdown. Increasing the dielectric constant through the DEA Reservoir can enhance output characteristics in response to electrical signals. This approach can be utilized in various applications in wearable devices, artificial muscles, and other fields. [ABSTRACT FROM AUTHOR]

Textiles are often used to protect people from cold environments. While most garments are designed for temperatures not far below 0 °C, very cold regions on the earth near the poles or on mountains necessitate special clothing. The same is true for homeless people who have few possibilities to warm up or workers in cooling chambers and other cold environments. Passive insulating clothing, however, can only retain body heat. Active heating, on the other hand, necessitates energy, e.g., by batteries, which are usually relatively heavy and have to be recharged regularly. This review gives an overview of energy-self-sufficient textile solutions for cold environments, including energy harvesting by textile-based or textile-integrated solar cells; piezoelectric sensors in shoes and other possibilities; energy storage in supercapacitors or batteries; and heating by electric energy or phase-change materials. [ABSTRACT FROM AUTHOR]

The load-adaptive behavior of the muscles in the human musculoskeletal system offers great potential for minimizing resource and energy requirements in many technical systems, especially in drive technology and robotics. However, the lack of knowledge about suitable technical linear actuators that can reproduce the load-adaptive behavior of biological muscles in technology is a major reason for the lack of successful implementation of this biological principle. In this paper, therefore, the different types of linear actuators are investigated. The focus is particularly on artificial muscles and rope pulls. The study is based on literature, on the one hand, and on two physical demonstrators in the form of articulated robots, on the other hand. The studies show that ropes are currently the best way to imitate the load-adaptive behavior of the biological model in technology. This is especially illustrated in the context of this paper by the discussion of different advantages and disadvantages of the technical linear actuators, where ropes, among other things, have a good mechanical and control behavior, which is very advantageous for use in an adaptive system. Finally, the next steps for future research are outlined to conclude how ropes can be used as linear actuators to transfer load-adaptive lightweight design into technical applications. [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]

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]

Comprehensive Summary: Spider silk has attracted increasing attention due to its fascinating combination of ultra‐high tenacity high strength, and excellent elasticity. Based on the fundamental biological studies on spider silk, significant research efforts have been devoted to biotechnology and chemical synthesis to mimic or even exceed the properties of natural spider silk fibers. Moreover, the natural spider silk fiber has been simulated with the burgeoning development of numerous spinning technologies, including wet spinning, dry spinning, electrostatic spinning, and microfluidic spinning, which continuously help to optimize the properties of synthetic spider silk. The unique characteristics of natural spider silk include high refraction transmission, heat resistance, antimicrobial properties, biocompatibility, and super shrinking. Biconical recreation of spider silk with special features and extraordinary capabilities demonstrates potential applications in biomedicine, smart wearables, artificial muscles and sensors, aerospace and other domains. [ABSTRACT FROM AUTHOR]

Copyright of Acta Mechanica Sinica is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Traditional rigid grippers that are used for underwater systems lack flexibility and have lower degrees of freedom. These systems might damage the underwater environment while conducting data acquisition and data sampling. Soft robotics, which is mainly focused on creating robots with extremely soft materials are more delicate for the grasping of objects underwater. These systems tend to damage the underwater ecosystem in the least possible way. In this paper, we have presented a simplified design of a soft arm inspired by the octopus arm actuated by coiled Shape Memory Alloys (SMAs) using completely flexible lightweight material. The characterization arm performance under various load and input current conditions is shown. We hope this work will serve as a basis for the future of underwater grasping utilizing soft robotics. [ABSTRACT FROM AUTHOR]

According to ISO/TR 23383, smart textiles reversibly interact with their environment and respond or adapt to changes in the environment. The present review and bibliometric analysis was performed on 5810 documents (1989–2022) from the Scopus database, using VOSviewer and Bibliometrix/Biblioshiny for science mapping. The results show that the field of smart textiles is highly interdisciplinary and dynamic, with an average growth rate of 22% and exponential growth in the last 10 years. Beeby, S.P., and Torah, R.N. have published the highest number of papers, while Wang, Z.L. has the highest number of citations. The leading journals are Sensors, ACS Applied Materials and Interfaces, and Textile Research Journal, while Advanced Materials has the highest number of citations. China is the country with the most publications and the most extensive cooperative relationships with other countries. Research on smart textiles is largely concerned with new materials and technologies, particularly in relation to electronic textiles. Recent research focuses on energy generation (triboelectric nanogenerators, thermoelectrics, Joule heating), conductive materials (MXenes, liquid metal, silver nanoparticles), sensors (strain sensors, self-powered sensors, gait analysis), speciality products (artificial muscles, soft robotics, EMI shielding), and advanced properties of smart textiles (self-powered, self-cleaning, washable, sustainable smart textiles). [ABSTRACT FROM AUTHOR]

Textiles composed of fibers can have their mechanical properties adjusted by changing the arrangement of the fibers, such as strength and flexibility. Particularly, in the case of smart textiles incorporating active materials, various deformations could be created based on fiber patterns that determine the directivity of active materials. In this study, we design a smart fiber-based textile actuator with a chain structure and evaluate its actuation characteristics. Smart fiber composed of shape memory alloy (SMA) generates deformation when the electric current is applied, causing the phase transformation of SMA. We fabricated the smart chain column and evaluated its actuating mechanism based on the size of the chain and the number of rows. In addition, a crochet textile actuator was designed using interlooping smart chains and developed into a soft gripper that can grab objects. With experimental verifications, this study provides an investigation of the relationship between the chain actuator's deformation, actuating force, actuator temperature, and strain. The results of this study are expected to be relevant to textile applications, wearable devices, and other technical fields that require coordination with the human body. Additionally, it is expected that it can be utilized to configure a system capable of flexible operation by combining rigid elements such as batteries and sensors with textiles. [ABSTRACT FROM AUTHOR]

Highlights: Convincing candidates of flexible (stretchable/compressible) electromagnetic interference shielding nanocomposites are discussed in detail from the views of fabrication, mechanical elasticity and shielding performance. Detailed summary of the relationship between deformation of materials and electromagnetic shielding performance. The future directions and challenges in developing flexible (particularly elastic) shielding nanocomposites are highlighted. With the extensive use of electronic communication technology in integrated circuit systems and wearable devices, electromagnetic interference (EMI) has increased dramatically. The shortcomings of conventional rigid EMI shielding materials include high brittleness, poor comfort, and unsuitability for conforming and deformable applications. Hitherto, flexible (particularly elastic) nanocomposites have attracted enormous interest due to their excellent deformability. However, the current flexible shielding nanocomposites present low mechanical stability and resilience, relatively poor EMI shielding performance, and limited multifunctionality. Herein, the advances in low-dimensional EMI shielding nanomaterials-based elastomers are outlined and a selection of the most remarkable examples is discussed. And the corresponding modification strategies and deformability performance are summarized. Finally, expectations for this quickly increasing sector are discussed, as well as future challenges. [ABSTRACT FROM AUTHOR]

Soft robotics aims to close the performance gap between built and biological machines through materials design. Soft robots are constructed from soft, actuatable materials to be physically intelligent, or to have traits that living organisms possess such as passive adaptability and morphological computation through their compliant, deformable bodies. However, materials selection for physical intelligence often involves low-performance and/or energy-inefficient, stimuli-responsive materials for actuation. Additional challenges in soft robot sensorization and control further limit the practical utility of these machines. Recognizing that electrically controllable materials are crucial for the development of soft machines that are both physically and computationally intelligent, we review progress in the development of electroprogrammable materials for soft robotic actuation. We focus on thermomechanical, electrostatic, and electrochemical actuation strategies that are directly controlled by electric currents and fields. We conclude with an outlook on the design and fabrication of next-generation robotic materials that will facilitate true bioinspired autonomy. [ABSTRACT FROM AUTHOR]

The engineering application of electrically responsive hydrogels is restricted by its hysteretic response as well as relatively small bending force and displacement. In this study, with macromolecular polysaccharide substance sodium alginate as the matrix, conductive nanoparticles were introduced to prepare a novel two-component flexible nanocomposites electroactive actuator using the vacuum drying method. First of all, the electroactive actuator was prepared with different dosage concentrations of silver nanoparticles (AgNPs). Secondly, the bending force and displacement testing devices were used to quantitively analyze the electroactive properties of samples with different dosage concentrations of AgNPs, e.g. bending force, deformability and response speed. Thirdly, the electrochemical method was applied to explore the variation pattern of the samples' electroactive properties based on parameters such as specific capacitance and resistance. Fourthly, the tensile strength, elongation break and modulus of elasticity of the materials were studied based on a microanalysis and an analysis of the materials' mechanical characteristics. The results show that the silver–sodium alginate nanocomposites electroactive actuator, with excellent electroactive characteristics, bending force and displacement, is applicable to biological electronic devices and micro electro mechanical systems. Fabrication processes of a conductive actuating membrane. (a) Schematic diagram of the fabrication steps for actuating membrane. (b) Schematic diagram of ion movement. (c) Premix of SA–AgNPs [ABSTRACT FROM AUTHOR]

Immersive technology, refers to various novel ways of creating and interacting with applications and experiences, e.g., virtual reality (VR), has been used in various simulations and training where preparing real/physical settings is not ideal or possible, or where the use of virtual contents is otherwise beneficial. Realizing realistic interactions with virtual content is crucial for a quality experience and the effectiveness of such simulation and training. In this paper, we propose a kinematics-based realistic hand interaction method to enable a physically plausible grip-lifting experience in VR. The method reflects three kinematic characteristics of the hand: the force at contact points, finger flexion, and the speed of hand/finger motion, and we developed a grip-lift interaction prototype using the proposed method. To examine the sense of realism and hand poses during the grip-lift interaction, we conducted a human subjects experiment using the prototype, resulting in positive effects on the perceived realism and usefulness of the interaction. Grip-lifting is a fundamental interaction technique that is involved in most embodied interaction scenarios. Our method would contribute to the design and development of realistic virtual experiences, of which we will discuss the implications and potential based on our findings. [ABSTRACT FROM AUTHOR]

Highlights: The dual-ion co-regulation system shortens ion migration pathways, which endow the yarn muscle with high contractile stroke (34.7%) and contractile rate (9.4% s−1), more than twice that of the "rocking-chair" -type ion migration yarn muscles. The yarn muscle shows high isometric stress of 18.4 MPa (61 times that of skeletal muscles) and 8 times the isometric stress of the "rocking-chair" -type yarn muscles at a higher frequency. The intercalation reaction between PF 6 - and collapsed carbon nanotubes allows the yarn muscle to achieve an energy-free high-tension catch state Artificial yarn muscles show great potential in applications requiring low-energy consumption while maintaining high performance. However, conventional designs have been limited by weak ion-yarn muscle interactions and inefficient "rocking-chair" ion migration. To address these limitations, we present an electrochemical artificial yarn muscle design driven by a dual-ion co-regulation system. By utilizing two reaction channels, this system shortens ion migration pathways, leading to faster and more efficient actuation. During the charging/discharging process, PF 6 - ions react with carbon nanotube yarn, while Li+ ions react with an Al foil. The intercalation reaction between PF 6 - and collapsed carbon nanotubes allows the yarn muscle to achieve an energy-free high-tension catch state. The dual-ion coordinated yarn muscles exhibit superior contractile stroke, maximum contractile rate, and maximum power densities, exceeding those of "rocking-chair" type ion migration yarn muscles. The dual-ion co-regulation system enhances the ion migration rate during actuation, resulting in improved performance. Moreover, the yarn muscles can withstand high levels of isometric stress, displaying a stress of 61 times that of skeletal muscles and 8 times that of "rocking-chair" type yarn muscles at higher frequencies. This technology holds significant potential for various applications, including prosthetics and robotics. [ABSTRACT FROM AUTHOR]

Artificial muscle fibers driven electrothermally with excellent properties of response, stroke, and work capacity are expected to serve in some intelligent structures and systems. However, muscle fibers that operate in subzero environments are highly needed in industrial production and aerospace applications but remain challenging. Herein, we reported a coaxial artificial muscle fiber by electrospinning a sheath of polycaprolactone (PCL) nanofibers on the surface of a carbon nanotube (CNT) fiber core, achieving the actuation in response to thermal at subzero temperatures. The CNT@PCL coaxial muscle fiber under 0.3 MPa achieved a maximum contractile stroke of ~18% as the temperature changed from −130°C to 45°C. The actuation mechanism at subzero temperatures of this muscle fiber was analyzed in combination with the temperature-deformation schematic curve of different polymers. Furthermore, a temperature sensor based on this muscle fiber was developed, due to the excellent linear relationship between the contraction and temperature. A 3D-printed prosthetic arm was designed to further exhibit the application demonstrations of this muscle fiber in subzero environments. This work provides new insights into artificial muscle fibers for serving in extreme environments with ultralow temperatures. [ABSTRACT FROM AUTHOR]

Hierarchically structured polymeric fibers, composed of structural nanoscale motifs that assemble into a microscale fiber are frequently found in natural fibers including cellulose and silk. The creation of synthetic fibers with nano-to-microscale hierarchical structures represents a promising avenue for the development of novel fabrics with distinctive physical, chemical, and mechanical characteristics. In this work, we introduce a novel approach for creating polyamine-based core–sheath microfibers with controlled hierarchical architectures. This approach involves a polymerization-induced spontaneous phase separation and subsequent chemical fixation. Through the use of various polyamines, the phase separation process can be manipulated to produce fibers with diverse porous core architectures, ranging from densely packed nanospheres to segmented "bamboo-stem" morphology. Moreover, the nitrogen-rich surface of the core enables both the chemisorption of heavy metals and the physisorption of proteins and enzymes. Our method offers a new set of tools for the production of polymeric fibers with novel hierarchical morphologies, which has a high potential for a wide range of applications such as filtering, separation, and catalysis. [ABSTRACT FROM AUTHOR]

Copyright of Acta Materiae Compositae Sinica is the property of Acta Materiea Compositae Sinica Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Stretchable yarn/fiber electronics with conductive features are optimal components for different wearable devices. This paper presents the construction of coil structure-based carbon nanotube (CNT)/polymer fibers with adjustable piezoresistivity. The composite unit fiber is prepared by wrapping a conductive carbon CNT sheath onto an elastic spandex core. Owing to the helical coil structure, the resultant CNT/polymer composite fibers are highly stretchable (up to approximately 300%) without a noticeable electrical breakdown. More specifically, based on the difference in the coil index (which is the ratio of the coil diameter to the diameter of the fiber within the coil) according to the polymeric core fiber (spandex or nylon), the composite fiber can be used for two different applications (i.e., as strain sensors or supercapacitors), which are presented in this paper. The coiled CNT/spandex composite fiber sensor responds sensitively to tensile strain. The coiled CNT/nylon composite fiber can be employed as an elastic supercapacitor with excellent capacitance retention at 300% strain. [ABSTRACT FROM AUTHOR]

A multifilament feeder was developed to achieve the high-throughput 3D printing of continuous carbon fiber–reinforced thermoplastic composites. Four filaments were supplied to the feeder and simultaneously printed by controlling the feeding speeds to quadruple the manufacturing volume. A water-resistant filament was also developed by the polymer blending of polyamide 6 (PA6) and polypropylene (PP), which provided good adhesion to the carbon fibers and water resistance, respectively. The polymer structure in the continuous carbon fiber–reinforced thermoplastic composites was characterized by scanning electron microscopy and energy-dispersive X-ray spectroscopy. The multilayer polymer structure was observed, which enhanced the water-resistant property. The bending test results revealed that the blending minimized the degradation of the flexural modulus of the 3D-printed unidirectional carbon fiber–reinforced thermoplastic composite under wet conditions. [ABSTRACT FROM AUTHOR]

Muscles are capable of modulating the body and adapting to environmental changes with a highly integrated sensing and actuation. Inspired by biological muscles, coiled/twisted fibers are adopted that can convert volume expansion into axial contraction and offer the advantages of flexibility and light weight. However, the sensing-actuation integrated fish line/yarn-based artificial muscles are still barely reported due to the poor actuation-sensing interface with off-the-shelf fibers. We report herein artificial coiled yarn muscles with self-sensing and actuation functions using the commercially available yarns. Via a two-step process, the artificial coiled yarn muscles are proved to obtain enhanced electrical conductivity and durability, which facilitates the long-term application in human-robot interfaces. The resistivity is successfully reduced from 172.39 Ω·cm (first step) to 1.27 Ω·cm (second step). The multimode sense of stretch strain, pressure, and actuation-sensing are analyzed and proved to have good linearity, stability and durability. The muscles could achieve a sensitivity (gauge factor, GF) of the contraction strain perception up to 1.5. We further demonstrate this self-aware artificial coiled yarn muscles could empower non-active objects with actuation and real-time monitoring capabilities without causing damage to the objects. Overall, this work provides a facile and versatile tool in improving the actuation-sensing performances of the artificial coiled yarn muscles and has the potential in building smart and interactive soft actuation systems. [ABSTRACT FROM AUTHOR]

A multifilament feeder was developed to achieve the high-throughput 3D printing of continuous carbon fiber--reinforced thermoplastic composites. Four filaments were supplied to the feeder and simultaneously printed by controlling the feeding speeds to quadruple the manufacturing volume. A water-resistant filament was also developed by the polymer blending of polyamide 6 (PA6) and polypropylene (PP), which provided good adhesion to the carbon fibers and water resistance, respectively. The polymer structure in the continuous carbon fiber--reinforced thermoplastic composites was characterized by scanning electron microscopy and energy-dispersive X-ray spectroscopy. The multilayer polymer structure was observed, which enhanced the water-resistant property. The bending test results revealed that the blending minimized the degradation of the flexural modulus of the 3D-printed unidirectional carbon fiber--reinforced thermoplastic composite under wet conditions. [ABSTRACT FROM AUTHOR]

Human muscles can grow and change their length with body development; therefore, artificial muscles that modulate their morphology according to changing needs are needed. In this paper, we report a strategy to transform an artificial muscle into a new muscle with a different morphology by thermodynamic-twist coupling, and illustrate its structural evolution during actuation. The muscle length can be continuously modulated over a large temperature range, and actuation occurs by continuously changing the temperature. This strategy is applicable to different actuation modes, including tensile elongation, tensile contraction and torsional rotation. This is realized by twist insertion into a fibre to produce torsional stress. Fibre annealing causes partial thermodynamic relaxation of the spiral molecular chains, which serves as internal tethering and inhibits fibre twist release, thus producing a self-supporting artificial muscle that actuates under heating. At a sufficiently high temperature, further relaxation of the spiral molecular chains occurs, resulting in a new muscle with a different length. A structural study provides an understanding of the thermodynamic-twist coupling. This work provides a new design strategy for intelligent materials. [ABSTRACT FROM AUTHOR]

The self-adaptive nature of smart textiles to the ambient environment has made them an indispensable part of emerging wearable technologies. However, current advances generally suffer from complex material preparation, uncomfortable fitting feeling, possible toxicity, and high cost in fabrication, which hinder the real-world application of smart materials in textiles. Herein, humidity-response torsional and tensile yarn actuators from twisted and coiled structures are developed using commercially available, cost-effective, and biodegradable viscose fibers based on yarn-spinning and weaving technologies. The twisted yarn shows a reversible torsional stroke of 1400° cm−1 in 5 s when stimulated by water fog with a spraying speed of 0.05 g s−1; the coiled yarn exhibits a peak tensile stroke of 900% upon enhancing the relative humidity. Further, textile manufacturing allows for the scalable fabrication to create fabric artificial muscles with high-dimensional actuation deformations and human-touch comfort, which can boost the potential applications of the humidly adaptive yarns in smart textile and advanced textile materials. [ABSTRACT FROM AUTHOR]

Astronauts suffer skeletal muscle atrophy in microgravity and/or zero-gravity environments. Artificial muscle-actuated exoskeletons can aid astronauts in physically strenuous situations to mitigate risk during spaceflight missions. Current artificial muscle fabrication methods are technically challenging to be performed during spaceflight. The objective of this research is to unveil the effects of critical operating conditions on artificial muscle formation and geometry in a newly developed helical fiber extrusion method. It is found that the fiber outer diameter decreases and pitch increases when the printhead temperature increases, inlet pressure increases, or cooling fan speed decreases. Similarly, fiber thickness increases when the cooling fan speed decreases or printhead temperature increases. Extrusion conditions also affect surface morphology and mechanical properties. Particularly, extrusion conditions leading to an increased polymer temperature during extrusion can result in lower surface roughness and increased tensile strength and elastic modulus. The shape memory properties of an extruded fiber are demonstrated in this study to validate the ability of the fiber from shape memory polymer to act as an artificial muscle. The effects of the operating conditions are summarized into a phase diagram for selecting suitable parameters for fabricating helical artificial muscles with controllable geometries and excellent performance in the future. [ABSTRACT FROM AUTHOR]

In recent years, the field of soft robotics has gained much attention by virtue of its aptness to work in certain environments unsuitable for traditional rigid robotics. Along with the uprising field of soft robotics is the increased attention to soft actuators which provide soft machines the ability to move, manipulate, and deform actively. This article provides a focused review of various high-performance and novel electrically driven soft actuators due to their fast response, controllability, softness, and compactness. Furthermore, this review aims to act as a reference guide for building electrically driven soft machines. The focus of this paper lies on the actuation principle of each type of actuator, comprehensive performance comparison across different actuators, and up-to-date applications of each actuator. The range of actuators includes electro-static soft actuators, electro-thermal soft actuators, and electrically driven soft pumps. [ABSTRACT FROM AUTHOR]

In this paper, we propose a novel and facile methodology to chemically construct a thin and highly compliant metallic electrode onto a twisted and coiled nylon-6 fiber (TCN) with a three-dimensional structure via surface modification of the TCN eliciting gold-sulfur (Au-S) interaction for enabling durable electro-thermally-induced actuation performance of a TCN actuator (TCNA). The surface of the TCN exposed to UV/Ozone plasma was modified to (3-mercaptopropyl)trimethoxysilane (MPTMS) molecules with thiol groups through a hydrolysis-condensation reaction. Thanks to the surface modification inducing strong interaction between gold and sulfur as a formation of covalent bonds, the Au electrode on the MPTMS-TCN exhibited excellent mechanical robustness against adhesion test, simultaneously could allow overall surface of the TCN to be evenly heated without any significant physical damages during repetitive electro-thermal heating tests. Unlike the TCNAs with physically coated metallic electrode, the TCNA with the Au electrode established on the MPTMS-TCN could produce a large and repeatable contractile strain over 12% as lifting a load of 100 g even during 2000 cyclic actuations. Demonstration of the durable electrode for the TCNA can lead to technical advances in artificial muscles for human-assistive devices as well as soft robots those requires long-term stability in operation. [ABSTRACT FROM AUTHOR]

Carbon fiber reinforced polymer (CFRP) composites are increasingly being used to strengthen structures and to retrofit existing structures. CFRP composites are used in various industries: construction, automotive, and many others. This literature review has shown that CFRP composites find numerous practical applications. Improving structures by reinforcing them with CFRP composite is an innovative approach in design. This review aims to explore the current state of the art in the types of structures that can be reinforced with CFRP, and modifications to the CFRP composite as an additional aspect to increase the strength of the reinforced structure. It has been shown that regardless of the type of reinforced material, the most critical element in this connection is the bonded joint. Proper surface preparation and the use of an appropriate adhesive are also important. [ABSTRACT FROM AUTHOR]

To achieve high durability and excellent mechanical performances of cementitious materials, research on fiber-reinforced cementitious composites (FRCC) containing various fibers has been actively conducted. On the other hand, in robotics and other fields, research on artificial muscles using Twisted and Coiled Polymer Actuator (TCPA), which have similar functions to human muscle fibers, has attracted much attention. In this study, use of this TCPA as a reinforcing fiber in high performance FRCC (HPFRCC) was proposed. The employed TCPA has a structure of coiled nylon fibers with wrapping stainless-steel fibers. The effect of the TCPA and its shrinkage motion on the crack dispersion properties of HPFRCC was investigated. The experimental results showed that the strain-hardening with multiple cracks in HPFRCC continued up to more than 7% of the ultimate strain when the TCPA was electrically stimulated to shrinkage motion. This information indicates that the TCPA has high potential to further improve HPFRCC performance. [ABSTRACT FROM AUTHOR]

Rehabilitation and mobility assistance using robotic orthosis or exoskeletons have shown potential in aiding those with musculoskeletal disorders. Artificial muscles are the main component used to drive robotics and bio-assistive devices. However, current fabrication methods to produce artificial muscles are technically challenging and laborious for medical staff at clinics and hospitals. This study aims to investigate a printhead system for material extrusion of helical polymer artificial muscles. In the proposed system, an internal fluted mandrel within the printhead and a temperature control module were used simultaneously to solidify and stereotype polymer filaments prior to extrusion from the printhead with a helical shape. Numerical simulation was applied to determine the optimal printhead design, as well as analyze the coupling effects and sensitivity of the printhead geometries on artificial muscle fabrication. Based on the simulation analysis, the printhead system was designed, fabricated, and operated to extrude helical filaments using polylactic acid. The diameter, thickness, and pitch of the extruded filaments were compared to the corresponding geometries of the mandrel to validate the fabrication accuracy. Finally, a printed filament was programmed and actuated to test its functionality as a helical artificial muscle. The proposed printhead system not only allows for the stationary extrusion of helical artificial muscles but is also compatible with commercial 3D printers to freeform print helical artificial muscle groups in the future. [ABSTRACT FROM AUTHOR]