Fabrication Of Soft Actuators Research Articles

3D‐printed biomimetic and bioinspired soft actuators

AbstractA major intent of scientific research is the replication of the behaviour observed in natural spaces. In robotics, these can be through biomimetic movements in devices and inspiration from diverse actions in nature, also known as bioinspired features. An interesting pathway enabling both features is the fabrication of soft actuators. Specifically, 3D‐printing has been explored as a potential approach for the development of biomimetic and bioinspired soft actuators. The extent of this method is highlighted through the large array of applications and techniques used to create these devices, as applications from the movement of fern trees to contraction in organs are explored. In this review, different 3D‐printing fabrication methods, materials, and types of soft actuators, and their respective applications are discussed in depth. Finally, the extent of their use for present operations and future technological advances are discussed.

Stiffness-tunable and self-sensing integrated soft machines based on 4D printed conductive shape memory composites

Through the synergy of nervous system and the self-regulation of muscle stiffness, living organisms are capable of quickly adjusting movements and actively adapting to dynamic environments. Likewise, the stiffness-changing and self-sensing functionalities are critical to empower soft robots with adjustable load capacity and agile movement. This work presents a paradigm for the design and fabrication of soft actuators with stiffness tunability and intrinsic self-sensing feedback through 4D printing method. The integration of 4D printed conductive composite into soft actuator body allows for stiffness adjustment within three orders of magnitude and ensures real-time stiffness-sensing, bending-sensing and pressure-sensing feedback. By constructing the theoretical deformation models and decoupling the resistance signals by machine learning methods, information on the stiffness, deformation and pressure of the material at different temperatures can be obtained. Cardiac-mimicking actuator and active therapeutic insoles are fabricated as proof-of-concept demonstrations, among which the active therapeutic insoles can perceive plantar pressure changes and conduct pressure-releasing actuation to ease the pain of patient at walk. It demonstrates the potential of this design approach for versatile applications such as medical assistive devices, artificial muscles, soft robotics, etc.

Harnessing fiber induced anisotropy in design and fabrication of soft actuator with simultaneous bending and twisting actuations

Most of the soft dielectric elastomer actuators (DEAs) are able to provide either planar or twisting deformations only. Development of a bio-inspired actuator with functionalities similar to the mammalian tongue or octopus tentacles is highly desirable for soft robotics applications. Here, design and fabrication of a multi-layered soft DEA capable of simultaneous bending and twisting actuation is reported through a unified computational and experimental approach. An anisotropic layer is introduced to couple the bending and twisting deformation in the conventional DEA. The fiber spacing and fiber orientation in the anisotropic layer is optimized with classical laminate theory (CLT) and finite element (FE) analysis. A multi-layered DEA with bending-twisting actuation is experimentally fabricated as a ‘proof of concept’. The computational and experimental results suggest that bend-twist coupling in multi-layered DEA can be suitably designed by varying the fiber spacing and orientation in the anisotropic layer. The twisting actuation of DEA enhances at the expense of bending deformation with an increase in the fiber angle. Finally, it is shown that a single anisotropic layer having 2 mm fiber spacing and 45° fiber orientation induces sufficiently large bending and twisting actuations in DEA. The findings of the present study will be a significant step ahead to develop bio-mimicking anisotropic actuators and grippers for soft robotics applications.

Photochemically and Photothermally Controllable Liquid Crystalline Network and Soft Walkers.

Developing intelligent soft robots capable to perform various responses to different stimulations has been a hot topic in recent years. Liquid crystalline networks (LCNs) have been considered as one of the most promising candidates in the fabrication of soft actuators because of the combination of elasticity of the polymer and anisotropy of the liquid crystals. However, the design and fabrication of advanced LCN materials with outstanding performances and multiple responsivities is highly demanded but still a challenge. In this work, a NIR-UV dual light-responsive LCN actuator was prepared by selectively coating a polydopamine (PDA) layer on an azobenzene-doped LCN film. This actuator presents UV responsivity in the uncoated region because of the photochemical isomerization of azobenzene and NIR sensitivity in the PDA-coated region originated from the striking photothermal effect. Thanks to the reprogrammable PDA coating, this dual-responsive LCN actuator was totally reprogrammable by coating and washing the PDA layer repeatedly. Based on the novel soft actuator, an artificial car that can imitate the switch of the "forward gear" to "neutral gear" of a real car was prepared. In normal mode, the actuator can move forward under NIR irradiation. After UV light excitation, the actuator cannot move under the same NIR irradiation, just like the car with the level in neutral. This novel actuator may provide inspirations for the fabrication of light-driven functional devices and soft actuators.

3-D printed soft magnetic helical coil actuators of iron oxide embedded polydimethylsiloxane

Soft actuators have grown to be a topic of great scientific interest. As the fabrication of soft actuators with conventional microfabrication methods are tedious, expensive, and time consuming, employment of 3-D printing fabrication methods appears promising as they can simplify fabrication and reduce the production cost. Complex structures can be fabricated with 3-D printing such as helical coils that can achieve actuation performances, which otherwise would be impossible with simpler geometries. In this study, development of soft magnetic helical coil actuators of iron oxide embedded polydimethylsiloxane (PDMS) was achieved with embedded 3-D printing techniques. Composites with three different weight ratios of 10 %, 20 %, and 30 % iron nanoparticles to PDMS were formulated. Using iron nanoparticles with the size of 15−20 nm helps preserve viscosity of the printing material low enough to print it with a small-bore needle (30-gauge, 180 micrometers inner diameter). The hydrogel support of Pluronic f-127 bath and the ability to maintain the ratio of the printed fiber’s diameter to coil diameter about 0.25 resulted in the successful fabrication and release of fabricated helical coil structures. This enabled 3-D printed structures characterized as magnetic actuators to achieve linear and bending actuation of more than 300 % and 80° respectively in the case of composites with 30 % iron oxide nanoparticles. Moreover, it was shown that the 3-D printed helical coils with 10 % iron oxide nanoparticles can be utilized as untethered soft robots capable of locomotion on 45 and 90 degrees inclines under an applied magnetic field.

Fabrication of soft actuator for extreme environment by molding of polyimide films

Fabrication of soft actuator for extreme environment by molding of polyimide films

Voltage-driven nonuniform axisymmetric torsion of a tubular dielectric elastomer actuator reinforced with one family of inextensible fibers

Abstract Dielectric elastomers (DEs) take the advantage of muscles-like voltage-induced giant deformation and have extensive applications in the fields of soft robots, adaptive optics and bioengineering. In the present work, the finite axisymmetric deformation with torsion of a tubular DE actuator reinforced by one family of inextensible helical fibers is studied by using the membrane theory . The voltage-driven torsional behavior of the DE actuator is caused by the asymmetric reinforcement of helical fibers. By adopting the Mooney-Rivlin elasticity model and the ideal dielectric model and accounting for the inextensibility of the helical fibers, a constitutive model is proposed for the fiber-reinforced DE actuator. Based on these modelling assumptions and considering the equilibrium equations and associated boundary conditions, a boundary value problem for the DE actuator is formulated and also solved numerically. Furthermore, the effects of material parameters and the fiber helical angle as well as mechanical loadings, including the internal pressure, axial force and twist moment, on the voltage-induced torsional behavior of the DE actuator are discussed. The developed model and revealed results are expected to aid the design and fabrication of soft actuators and soft robots.

Controllable helical deformations on printed anisotropic composite soft actuators

Helical shapes are ubiquitous in both nature and engineering. However, the development of soft actuators and robots that mimic helical motions has been hindered primarily due to the lack of efficient modeling approaches that take into account the material anisotropy and the directional change of the external loading point. In this work, we present a theoretical framework for modeling controllable helical deformations of cable-driven, anisotropic, soft composite actuators. The framework is based on the minimum potential energy method, and its model predictions are validated by experiments, where the microarchitectures of the soft composite actuators can be precisely defined by 3D printing. We use the developed framework to investigate the effects of material and geometric parameters on helical deformations. The results show that material stiffness, volume fraction, layer thickness, and fiber orientation can be used to control the helical deformation of a soft actuator. In particular, we found that a critical fiber orientation angle exists at which the twist of the actuator changes the direction. Thus, this work can be of great importance for the design and fabrication of soft actuators with tailored deformation behavior.

Elastic Inflatable Actuators for Soft Robotic Applications.

The 20th century's robotic systems have been made from stiff materials, and much of the developments have pursued ever more accurate and dynamic robots, which thrive in industrial automation, and will probably continue to do so for decades to come. However, the 21st century's robotic legacy may very well become that of soft robots. This emerging domain is characterized by continuous soft structures that simultaneously fulfill the role of robotic link and actuator, where prime focus is on design and fabrication of robotic hardware instead of software control. These robots are anticipated to take a prominent role in delicate tasks where classic robots fail, such as in minimally invasive surgery, active prosthetics, and automation tasks involving delicate irregular objects. Central to the development of these robots is the fabrication of soft actuators. This article reviews a particularly attractive type of soft actuators that are driven by pressurized fluids. These actuators have recently gained traction on the one hand due to the technology push from better simulation tools and new manufacturing technologies, and on the other hand by a market pull from applications. This paper provides an overview of the different advanced soft actuator configurations, their design, fabrication, and applications.

Analytical Solutions for Inextensible Fiber-Reinforced Dielectric Elastomer Torsional Actuators

Two types of tubular dielectric elastomers (DE) torsional actuators are studied in this work, which are, respectively, reinforced by a family and two families of helical inextensible fibers. When subject to a radial electric field, torsional deformation will be induced in the DE actuators due to the constraint of inextensible fibers. By conducting finite deformation analysis with the principal axis approach and adopting appropriate constitutive equations, simple analytical solutions are obtained for the considered DE actuators. Furthermore, the effects of material parameters and the fiber angles as well as externally applied axial force and twist moment on the voltage-induced torsional behaviors of the two DE actuators are discussed in order to explore their maximum torsional actuation capability. The concept design presented here provides an effective approach for achieving large torsional deformation, and the developed model and revealed results will aid the design and fabrication of soft actuators and soft robots.