High-performance Actuators Research Articles

A graphene-based photo-electro-thermal metamaterial for soft fixtures with superior grasping performance.

Soft actuators are valued for their adaptability and diverse applications but often face challenges like slow response, high activation energy, and high energy consumption. To address these issues, we developed a graphene-assembled film (GAF) via the redox method, characterized by high thermal conductivity, conductivity, and stiffness. Using GAF as a photothermal and electrothermal driver, we engineered a sandwich-structured metamaterial (SSM) by combining two polymers with vastly different thermal expansion coefficients. The SSM achieved rapid response (<5 s), low actuation energy (≤0.22W cm⁻2 or ≤3.55 V), and large bending curvature (>0.18mm⁻1), surpassing conventional designs in response speed (226.2% faster) and curvature (249.1% higher). This metamaterial enables soft fixtures with superior gripping capabilities and low energy consumption, handling up to eight times the object mass of traditional designs. This work highlights advances in multi-stimulus metamaterials, offering significant implications for the development of high-performance soft actuators.

A high-performance elastic-soft hybrid pneumatic actuator with origami structure

A high-performance elastic-soft hybrid pneumatic actuator with origami structure

Improved Multiobjective Optimization of Tubular Slotless Permanent Magnet Linear Synchronous Motor for High-Performance Z-Axis Actuators

Improved Multiobjective Optimization of Tubular Slotless Permanent Magnet Linear Synchronous Motor for High-Performance Z-Axis Actuators

Electro-thermal responses polymer systems with continuous shape memory alloys: Merging rapid shape memory and color transitions

Electro-thermal responses polymer systems with continuous shape memory alloys: Merging rapid shape memory and color transitions

Ultralow Voltage High-Performance Nanocellulose-Based Electro-Ionic Actuators for Soft Robots.

High-performance eco-friendly soft actuators showing large displacement, fast response, and long-term operational capability require further development for next-generation bioinspired soft robots. Herein, we report an electro-ionic soft actuator based on carboxylated cellulose nanocrystals (CCNC) and carboxylated cellulose nanofibers (CCNF), graphene nanoplatelets (GN), and ionic liquid (IL). The actuator exhibited exceptional actuation performances, achieving large displacements ranging from 1.6 to 12.3 mm under ultralow actuation voltages of 0.25-1.5 V. It also operated stably across a broad frequency band from 0.1 to 10 Hz and displayed a significant working stability of 99.3% after up to 240 cycles. Remarkably, the electro-active actuator demonstrated a fast response (0.39 s delay under 1.0 V at 0.1 Hz), and a long lifespan (with only a minor decrease of 2% for 2 years). The enhanced actuation performances of the actuator were attributed to its superior ionic conductivity, high charge storage ability, strong ionic interaction, and physical-chemical cross-linked networks. Furthermore, we successfully demonstrated the bioinspired applications of CCNC/CCNF-IL-GN actuators including micro-grippers, spiral-structure electroactive stents, biomimetic fingers, and bionic dragonfly wings. The proposed actuator and its bioinspired robot designs could offer a significant way for the development of next-generation eco-friendly soft actuators, soft robots, and biomedical microdevices in microenvironments requiring low-voltage environment.

Bio-inspired piezoelectric stick-slip actuation: Synergistic bridge-type and leveraged amplification mechanism via rowing-motion mimicry.

This paper presents the development of a new bionic piezoelectric stick-slip actuator (PSSA). This actuator is designed to simulate the human rowing motion. By synergizing a lever amplification structure with a bridge amplification mechanism, the design not only mimics the rowing motion, where the lever amplification structure acts like an oar and the bridge amplification mechanism resembles the force exerted by a person operating the oar, but also suppresses the problem of backward displacement in traditional PSSAs. Finite element analysis and experimental results demonstrate the feasibility of the design, with a peak velocity of 17.48 mm/s and a maximum load capacity of 55g. Comparative experiments have shown that the rowing-motion piezoelectric actuation mode outperforms the traditional PSSA mode, with a 16.8% increase in peak velocity and a 120% increase in load capacity. The innovative design has significant implications for the development of high-performance actuators.

Slippery liquid-infused porous surfaces for high-performance moisture-responsive actuators

Smart actuators convert environmental changes into mechanical energy. However, the actuation performance and robustness of smart actuators are limited by the weak interlaminar force and poor adhesion between layers. Herein, we report moisture-responsive actuators integrated with slippery liquid-infused porous surfaces (SLIPSs). The difference in adsorption capacity of water molecules further increases because the SLIPS layer is isolated from air by the lubricating oil film. Compared with the initial (graphene oxide/candle soot, GO/CS) bilayer film, the integrated SLIPS layer improved the bending performance by 12.6% and shortened the response–recovery time by one-third. Moreover, the GO/SLIPS actuator exhibited excellent long-term stability over 10 000 cycles due to the lubricating oil's capillary fluidity. In addition, a moisture-controlled water-transport device based on a GO/SLIPS film was demonstrated.

High-Performance SAW-Based Microfluidic Actuators Composed of Sputtered Al–Cu IDT Electrodes

To realize highly sensitive SAW devices, novel Al–Cu thin films were developed using a combinatorial sputtering system. The Al–Cu sample library exhibited a wide range of chemical compositions and electrical resistivities, providing valuable insights for selecting optimal materials for SAW devices. Considering the significant influence of electrode resistivity and density on acoustic wave propagation, an Al–Cu film with 65 at% Al was selected as the IDT electrode material. The selected Al–Cu film demonstrated a resistivity of 6.0 × 10−5 Ω-cm and a density of 4.4 g/cm3, making it suitable for SAW-based microfluidic actuator applications. XRD analysis revealed that the Al–Cu film consisted of a physical mixture of Al and Cu without the formation of Al–Cu alloy phases. The film exhibited a fine-grained microstructure with an average crystallite size of 7.5 nm and surface roughness of approximately 6 nm. The SAW device fabricated with Al–Cu IDT electrodes exhibited excellent acoustic performance, resonating at 143 MHz without frequency shift and achieving an insertion loss of −13.68 dB and a FWHM of 0.41 dB. In contrast, the Au electrode-based SAW device showed significantly degraded acoustic characteristics. Moreover, the SAW-based microfluidic module equipped with optimized Al–Cu IDT electrodes successfully separated 5 μm polystyrene (PS) particles even at high flow rates, outperforming devices with Au IDT electrodes. This enhanced performance can be attributed to the improved resonance characteristics of the SAW device, which resulted in a stronger acoustic radiation force exerted on the PS particles.

A new type of arc-plate flexible driving foot stick-slip piezoelectric actuator

Abstract Because of its high precision and high speed, stick-slip actuators in piezoelectric actuators have important research significance in aerospace and other fields. To make the performance of the actuator superior, a high-performance stick-slip actuator suitable for the aerospace field is developed. In this paper, based on the in-depth study of the related theories, a kind of arc-plate flexible driving foot is proposed. On this basis, a kind of arc-plate flexible driving foot stick-slip piezoelectric actuator is designed to further improve the performance of the actuator. After the test, its maximum speed can reach 4.12 mm/s, and the maximum load is 330 g.

Interfacially Fabricated Covalent Organic Framework Membranes for Film-Based Fluorescence Humidity Sensors and Moisture Driven Actuators.

Rapid, on-site measurement of ppm-level humidity in real time remains a challenge. In this work, we fabricated a few micrometer thick, β-ketoenamine-linked covalent organic framework (COF) membrane via interfacially confined condensation of 1,3,5-tris-(4-aminophenyl)triazine (TTA) with 1,3,5-tri-formylphloroglucinol (TP). Based on the super-sensitive and reversible response of the COF membrane to water vapor, we developed a high-performance film-based fluorescence humidity sensor, depicting unprecedented detection limit of 0.005 ppm, fast response/recovery (2.2 s/2.0 s), and a detection range from 0.005 to 100 ppm. Remarkably, more than 7,000-time continuous tests showed no observable change in the performance of the sensor. The applicability of the sensor was verified by on-site and real-time monitoring of humidity in a glovebox. The superior performance of the sensor was ascribed to the highly porous structure and unique affinity of the COF membrane to water molecules as they enable fast mass transfer and efficient utilization of the water binding sites. Moreover, based on the remarkable moisture driven deformation of the COF membrane and its composition with the known polyimide films, some conceptual actuators were created. This study brings new ideas to the design of ultra-sensitive film-based fluorescent sensors (FFSs) and high-performance actuators.

Defect Dipole Asymmetry Response Induces Electrobending Deformation in Thin Piezoceramics.

Ultrahigh electrostrains (>1%) in several piezoceramic systems have been reported since 2022, which attracts more and more interest in the field of piezoelectricity; however, the mechanism is still unclear. Here, in nonstoichiometric (K_{0.48}Na_{0.52})_{0.99}NbO_{2.995} ceramics, we have directly observed a novel electric field-induced bending (electrobending) phenomenon that visually exhibits an alternating concave-convex deformation under an electric field of ±50 kV cm^{-1}, leading to the measured ultrahigh electrostrain. It is demonstrated that the electrobending deformation arises from the different stresses due to the stretching or compression of the oriented-defect dipoles in the upper and lower surface layers of the ceramics under an electric field. Consequently, a giant apparent electrostrain of 31.8% is obtained at room temperature. Our discovery is an important addition and refinement to the field of condensed matter physics, while also providing a new strategy and shedding light on the design of future high-performance actuators and intelligent devices.

Environmentally Friendly, Dual-Responsive Actuator Based on Nafion, Carboxylated Multiwalled Carbon Nanotubes, and Polyethylene.

As a type of smart material, flexible stimulus-responsive actuators have become a hot research topic nowadays. However, flexible actuators responding to a single stimulus source are susceptible to external perturbations, which may lead to an unstable function or even failure. Therefore, in this paper, we proposed a bilayer actuator that can be driven by both humidity and light by combining the humidity-sensitive Nafion, carboxylated multiwalled carbon nanotubes (cMWCNT) with excellent photothermal conversion properties, and commercial polyethylene (PE) tape with good humidity insensitivity and thermal expansion. First, the cMWCNT-Nafion film was prepared by a solution casting method and bonded together with PE tape to obtain a bilayer actuator. Then, the effects of the cMWCNT mass fraction and film thickness on the humidity and light response performance of the bilayer actuator were investigated. The optimal ratios of raw materials were obtained for different stimulation sources, respectively. Furthermore, the performance of the bilayer actuator with the optimal ratios was tested; it was verified that the proposed dual-responsive actuator can realize different degrees of bending deformation under different relative humidity (RH) and ultraviolet (UV) light intensity with good stability. Finally, the application potential in multiple scenarios was further verified by applying the prepared cMWCNT-Nafion/PE bilayer actuator to a smart window, crawling robot, and flexible gripper. This paper will provide a meaningful reference for the development and performance optimization of high-performance dual-responsive actuators.

Sulphonated-graphene oxide nanocomposite membranes with PVA-ZnO nanostructures and mechanized agitation-enhanced pt coating for soft robotics bending actuator

Ionic Polymer-Metal Composite (IPMC) actuators have garnered significant scientific attention in robotics and artificial muscles for their ability to operate at low voltage, high strain capacity, and lightweight construction. The lack of uniform bending in IPMC actuators undermines their control precision and restricts their range of potential applications. This study utilized the unique properties of nanoscale materials and Polyvinyl alcohol (PVA) to develop a membrane for soft robotic bending actuation. Subsequently, a platinum coating was applied to the membrane to mitigate the limitations of IPMCs in soft robotics applications. Herein, mechanized agitation was employed during the solution-casting process to enhance platinum metal (Pt-metal) coating on zinc oxide (ZnO) nanostructures within a PVA- sulphonated graphene oxide nanocomposite, achieving enhanced soft robotics bending actuation capabilities. The resultant membrane composed of sulphonated-graphene oxide and polyvinyl-zinc oxide coated with pt (PsGZ-Pt) was examined by exploring advanced analytical techniques such as Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction spectroscopy (XRD). Furthermore, the ionic exchange capacity (IEC), proton conductivity (PC), water uptake and water loss characteristics were evaluated to be 2.1 meq. g−1, 1.95 × 10−3 Scm−1, 59.62% at 45 °C and water loss at 9 min immersion found 38%, respectively. Electromechanical studies of the PsGZ-Pt membrane (size 30 mm length, 10 mm width, 0.07 mm thickness) showed an actuation force of 0.3253 mN and a displacement of roughly 22.8 mm at ± 3 VDC. These findings highlighted the PsGZ-Pt membrane’s potential as a low-cost alternative to expensive commercial IPMC actuators based on polymers. These results presented a straightforward, low-cost approach for synthesizing PsGZ-Pt utilizing conventional technologies. The PsGZ-Pt membrane shows promise for generating low-cost, high-performance actuation materials with a wide range of industrial applications.

The role of water mobility on water-responsive actuation of silk

Biological water-responsive materials that deform with changes in relative humidity have recently demonstrated record-high actuation energy densities, showing promise as high-performance actuators for various engineering applications. However, there is a lack of theories capable of explaining or predicting the stress generated during water-responsiveness. Here, we show that the nanoscale confinement of water dominates the macroscopic dehydration-induced stress of the regenerated silk fibroin. We modified silk fibroin’s secondary structure, which leads to various distributions of bulk-like mobile and tightly bound water populations. Interestingly, despite these structure variations, all silk samples start to exert force when the bound-to-mobile (B/M) ratio of confined water reaches the same level. This critical B/M water ratio suggests a common threshold above which the chemical potential of water instigates the actuation. Our findings serve as guidelines for predicting and engineering silk’s WR behavior and suggest the potential of describing the WR behavior of biopolymers through confined water.

Construction of MXene interlayer conductive ion transport channel by polypyrrole-coated cellulose nanofibers for ultralow voltage high-performance ionic soft actuators

Construction of MXene interlayer conductive ion transport channel by polypyrrole-coated cellulose nanofibers for ultralow voltage high-performance ionic soft actuators

A Pneumatic Flexible Linear Actuator Inspired by Snake Swallowing.

Soft robots spark a revolution in human-machine interaction. However, developing high-performance soft actuators remains challenging due to trade-offs among output force, driving distance, control precision, safety, and compliance. Here, addressing the lack of long-distance, high-precision flexible linear actuators, an innovative pneumatic flexible linear actuator (PFLA) is introduced, inspired by the smooth and controlled process observed in snakes ingesting sizable food, such as eggs. This PFLA combines a soft tube, emulating the snake's body cavity, with a pneumatically driven piston. Through the joint modulation of moving resistance and driving force by pneumatic pressure, the PFLA exhibits exceptional motion control capabilities, including self-holding without pressure supply, smooth low-speed motion (down to 0.004 m s-1), high-speed motion (up to 5.6 m s-1) with low air pressure demand, and a self-protection mechanism. Highlighting its adaptability and versatility, the PFLA finds applications in various settings, including a wearable assistive devices, a manipulator capable of precise path tracking and positioning, and rapid transportation in diverse environments for pipeline inspection and firefighting. This PFLA combines biomimetic principles with sophisticated fluidic actuation to achieve long-distance, flexible, precise, and safe actuation, offering a more adaptive solution for force/motion transmission, particularly in challengingenvironments.

Acoustofluidic Diversity Achieved by Multiple Modes of Acoustic Waves Generated on Piezoelectric-Film-Coated Aluminum Sheets.

Excitation of multiple acoustic wave modes on a single chip is beneficial to implement diversified acoustofluidic functions. Conventional acoustic wave devices made of bulk LiNbO3 substrates generally generate few acoustic wave modes once the crystal-cut and electrode pattern are defined, limiting the realization of acoustofluidic diversity. In this paper, we demonstrated diversity of acoustofluidic behaviors using multiple modes of acoustic waves generated on piezoelectric-thin-film-coated aluminum sheets. Multiple acoustic wave modes were excited by varying the ratios between IDT pitch/wavelength and substrate thickness. Through systematic investigation of fluidic actuation behaviors and performances using these acoustic wave modes, we demonstrated fluidic actuation diversities using various acoustic wave modes and showed that the Rayleigh mode, pseudo-Rayleigh mode, and A0 mode of Lamb wave generally have better fluidic actuation performance than those of Sezawa mode and higher-order modes of Lamb wave, providing guidance for high-performance acoustofluidic actuation platform design. Additionally, we demonstrated diversified particle patterning functions, either on two sides of acoustic wave device or on a glass sheet by coupling acoustic waves into the glass using the gel. The pattern formation mechanisms were investigated through finite element simulations of acoustic pressure fields under different experimental configurations.

Fast Responsive and High-Strain Electro-Ionic Soft Actuator Based on the 3D-Structure MXene-EGaIn/MXene Bilayer Composite Electrode.

Electro-ionic soft actuators have garnered significant attention owing to their promising applications in flexible electronics, wearable devices, and soft robotics. However, achieving high actuation performance (large bending strain and fast response time) of these soft actuators under low voltage has been challenging due to issues related to ion diffusion and accumulation. In this study, an electro-ionic soft actuator is fabricated using Ti3C2Tx MXene and eutectic gallium-indium (EGaIn) composite material as the bilayer electrode and methylammonium formate/1-ethyl-3-methylimidazolium tetrafluoroborate/poly(vinylidene fluoride) (MAF-EMIMBF4/PVDF) as the ionic liquid-type electrolyte. The research results indicate that the prepared soft actuator exhibits excellent actuation performance with a peak-to-peak displacement of 35 mm and a bending strain of 0.69% (a peak-to-peak strain of 1.38%) under a low voltage (3 V). The electro-ionic soft actuator shows a wide frequency range (0.1-10 Hz), fast response time (0.35 s), and a rise time of 7.5 s. Furthermore, it demonstrates good cyclic durability, with a retention rate of 92.5% of its performance for 10 000 cycles. These excellent performances are attributed to the 3D structure of the Ti3C2Tx-EGaIn/Ti3C2Tx bilayer composite electrode, as well as the characteristics of the low viscosity, high conductivity, small ion volume, and larger volume difference between cations and anions in MAF ionic liquid. The high-performance electro-ionic soft actuator can be used in various fields such as artificial muscles, tactile devices, and soft robots.

Polyelectrolyte-Mediated Modulation of Spatial Internal Stresses of Hydrogels for Complex 3D Actuators.

Hydrogel actuators with complex 3D initial shapes show numerous important applications, but it remains challenging to fabricate such actuators. This article describes a polyelectrolyte-based strategy for modulating small-scale internal stresses within hydrogels to construct complex actuators with tailored 3D initial shapes. Introducing polyelectrolytes into precursor solutions significantly enhances the volume shrinkage of hydrogel networks during polymerization, allowing us to modulate internal stresses. Photopolymerization of these polyelectrolyte-containing solutions through a mask produces mechanically strong hydrogel sheets with large patterned internal stresses. Consequently, these hydrogel sheets attain complex 3D initial shapes at equilibrium, in contrast to the planar initial configuration of 2D actuators. We demonstrate that these 3D actuators can reversibly transform into other 3D shapes (i.e., 3D-to-3D shape transformations) in response to external stimuli. Additionally, we develop a predictive model based on the Flory-Rehner theory to analyze the polyelectrolyte-mediated shrinking behaviors of hydrogel networks during polymerization, allowing precise modulation of shrinkage and internal stress. This polyelectrolyte-boosted shrinking mechanism paves a route to the fabrication of high-performance 3D hydrogel actuators.

Full-scale hybrid fire test in real-time with multiple degree of freedom

Full-scale hybrid fire test in real-time with multiple degree of freedom