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The modeling of soft structures, actuators, and sensors is challenging, primarily due to the high nonlinearities involved in such soft robotic systems. Finite element modeling (FEM) is an effective technique to represent soft and deformable robotic systems containing geometric nonlinearities due to large mechanical deformations, material nonlinearities due to the inherent nonlinear behavior of the materials (i.e., stress-strain behavior) involved in such systems, and contact nonlinearities due to the surfaces that come into contact upon deformation. Prior to the fabrication of such soft robotic systems, FEM can be used to predict their behavior efficiently and accurately under various inputs and optimize their performance and topology to meet certain design and performance requirements. In this article, we present the implementation of FEM in the design process of directly three-dimensional (3D) printed pneumatic soft actuators and sensors to accurately predict their behavior and optimize their performance and topology. We present numerical and experimental results to show that this approach is very effective to rapidly and efficiently design the soft actuators and sensors to meet certain design requirements and to save time, modeling, design, and fabrication resources.

Pneumatic artificial muscles are pneumatic devices with practical and various applications as common actuators. They, as human muscles, work in agonistic-antagonistic way, giving a traction force only when supplied by compressed air. The state of the art of soft pneumatic actuators is here analyzed: different models of pneumatic muscles are considered and evolution lines are presented. Then, the use of Pneumatic Muscles (PAM) in rehabilitation apparatus is described and the general characteristics required in different applications are considered, analyzing the use of proper soft actuators with various technical properties. Therefore, research activity carried out in the Department of Mechanical and Aerospace Engineering in the field of soft and textile actuators is presented here. In particular, pneumatic textile muscles useful for active suits design are described. These components are made of a tubular structure, with an inner layer of latex coated with a deformable outer fabric sewn along the edge. In order to increase pneumatic muscles forces and contractions Braided Pneumatic Muscles are studied. In this paper, new prototypes are presented, based on a fabric construction and various kinds of geometry. Pressure-force-deformation tests results are carried out and analyzed. These actuators are useful for rehabilitation applications. In order to reproduce the whole upper limb movements, new kind of soft actuators are studied, based on the same principle of planar membranes deformation. As an example, the bellows muscle model and worm muscle model are developed and described. In both cases, wide deformations are expected. Another issue for soft actuators is the pressure therapy. Some textile sleeve prototypes developed for massage therapy on patients suffering of lymph edema are analyzed. Different types of fabric and assembly techniques have been tested. In general, these Pressure Soft Actuators are useful for upper/lower limbs treatments, according to medical requirements. In particular devices useful for arms massage treatments are considered. Finally some applications are considered.

Moldable polymers, such as polydimethylsiloxane (PDMS), are widely used for microstructures. Various PDMS microstructures have been developed by molding and applied to microfluidic devices. In addition to the moldability of PDMS, its elasticity, optical transparency, gas permeability, and biocompatibility facilitate its utilization in diverse applications. However, the permeability of PDMS makes it unsuitable in cases that require sealing. For instance, inflatable soft devices, including pneumatic balloon actuators, require their constituent material to exhibit both elastic and impermeable features to utilize driving pressure effectively. In this context, this paper presents the poly‐para‐xylylene (parylene)‐caulking of PDMS without losing elasticity of PDMS. Parylene‐caulked PDMS is obtained by etching coated parylene on PDMS. In the context of the previous study on parylene‐caulked PDMS and similar works published recently, updated surface analysis results, and prepolymer ratio dependences are reported in this paper. Surface analysis is performed based on Fourier transform infrared spectrometry and time‐of‐flight secondary ion mass spectrometry is used to examine the presence of parylene on and inside the PDMS superficial layer. Parylene‐caulked PDMS is attractive for inflatable soft actuators. This study believes that these results will potentially contribute to a wide range of applications that require gas impermeability. This study investigates poly‐para‐xylylene (parylene)‐caulking of polydimethylsiloxane (PDMS) without loss of its elasticity for use in inflatable soft devices such as a pneumatic balloon actuator (PBA). This study reports updated results using time‐of‐flight secondary ion mass spectrometry and the dependence of characteristics on prepolymer ratio. This study has applied parylene‐caulked PDMS to PBA that requires both elasticity and gaseous impermeability.

Applying soft actuators to hand motion assist for rehabilitation has been receiving increasing interest in recent years. Pioneering research efforts have shown the feasibility of soft rehabilitation gloves (SRGs). However, one important and practical issue, the effects of users’ individual differences in finger size and joint stiffness on both bending performance (e.g., Range of motion (ROM) and torque) and the mechanical loads applied to finger joints when the actuators are placed on a patient’s hand, has not been well investigated. Moreover, the design considerations of SRGs for individual users, considering individual differences, have not been addressed. These, along with the inherent safety of soft actuators, should be investigated carefully before the practical use of SRGs. This work aimed to clarify the effects of individual differences on the actuator’s performance through a series of experiments using dummy fingers designed with individualized parameters. Two types of fiber-reinforced soft actuators, the modular type for assisting each joint and conventional (whole-finger assist) type, were designed and compared. It was found that the modular soft actuators respond better to individual differences set in the experiment and exhibit a superior performance to the conventional ones. By suitable connectors and air pressure, the modular soft actuators could cope with the individual differences with minimal effort. The effects of the individualized parameters are discussed, and design considerations are extracted and summarized. This study will play an important role in pushing forward the SRGs to real rehabilitation practice.

Developing a multiresponsive and multifunctional soft actuator that can output mechanical deformation is crucial to the fields of soft robotics and wearable devices. Herein, a 2D metallic molybdenum disulfide (MoS2)‐based soft actuator with dual‐response and self‐sensing function is designed and fabricated. By using the outstanding photothermal property of 1T phase MoS2, good electrical property and network structure of carbon nanotubes (CNTs), hygroscopic expansion of paper, and thermal expansion of polyimide (PI), the MoS2‐based actuator can respond to external voltage and light stimulation and produce rapid and large bending deformation. In addition, the actuator can be used as a flexible strain sensor to realize real‐time sensing of bending deformation by using piezoresistive property of the MoS2–CNT composite film. Based on this soft actuator, a flexible mechanical gripper that can manipulate soft objects with irregular shape and intelligent wearable gloves that can automatically close to block the light irradiation are made. Furthermore, combined with the sensing feature of this MoS2‐based actuator, the gripper with integrated sensing function is also developed. These results indicate the great prospect of the MoS2‐based actuator in intelligent soft mechanical devices, robots, and wearable systems. A dual‐responsive MoS2‐based soft actuator is fabricated, which not only shows good electrical/optical‐induced actuation with large deformation, but also exhibits strain sensing function. Based on these actuators, a flexible mechanical gripper for manipulation of the objects is constructed. Meanwhile, the mechanical gripper can also realize the integrated sensing of its own light‐induced grasping process, revealing its great application potential.

Soft wearable actuators must align with anatomical joints, conform to limb geometry, and operate at low pneumatic pressures. Yet most twisting mechanisms rely on bulky attachment interfaces and relatively high actuation pressures, limiting practicality in assistive applications. This study introduces the first Twisting Soft Sleeve Actuator (TSSA), a self-contained, wearable actuator that produces controlled bidirectional torsion. The design integrates helically folded bellows with internal stabilization layers to suppress radial expansion and enhance torque transmission. The TSSA is fabricated from thermoplastic polyurethane using a Bowden-type fused filament fabrication (FFF) process optimized for airtightness and flexibility. Performance was characterized using a modular test platform that measured angular displacement and output force under positive pressure (up to 75 kPa) and vacuum (down to −85 kPa). A parametric study evaluated the effects of fold width, fold angle, wall thickness, and twist angle. Results demonstrate bidirectional, self-restoring torsion with clockwise rotation of approximately 30 degrees and a peak output force of about 40 N at 75 kPa, while reverse torsional motion occurred under vacuum actuation. The TSSA enables anatomically compatible, low-pressure torsion, supporting scalable, multi-degree-of-freedom sleeve systems for wearable robotics and rehabilitation.

To receive a greater power and to demonstrate the soft bellows-shaped actuator’s wireless actuation, micro inductors were built for wireless power transfer and realized in a three-dimensional helical structure, which have previously been built in two-dimensional spiral structures. Although the three-dimensional helical inductor has the advantage of acquiring more magnetic flux linkage than the two-dimensional spiral inductor, the existing microfabrication technique produces a device on a two-dimensional plane, as it has a limit to building a complete three-dimensional structure. In this study, by using a three-dimensional printed soluble mold technique, a three-dimensional heater with helical coils, which have a larger heating area than a two-dimensional heater, was fabricated with three-dimensional receiving inductors for enhanced wireless power transfer. The three-dimensional heater connected to the three-dimensional helical inductor increased the temperature of the liquid and gas inside the bellows-shaped actuator while reaching 176.1% higher temperature than the heater connected to the two-dimensional spiral inductor. Thereby it enables a stroke of the actuator up to 522% longer than when it is connected to the spiral inductor. Therefore, three-dimensional micro coils can offer a significant approach to the development of wireless micro soft robots without incurring heavy and bulky parts such as batteries.

In the case of the treatment of low back pain, the lumbar corset which is the orthotic therapy is mainly used. However, there is a problem that the trunk muscle group is not used continuously by wearing the conventional lumbar corset for a long time, and muscle decline may occur. In this research, we propose an intelligent pneumatic corset that detects the forward bending posture with a sensor and automatically drives the soft actuator according to the attitude angle. It detects a forward-leaning posture in which the burden on the lumbar region increases, and automatically pressurizes the soft actuator. And, in the corset developed so far, the effect of supporting the muscle of the lumbar region was expected by compressing the abdomen and increasing abdominal pressure. In this paper, the operation support method by the restorative force when the soft actuator is deformed and the design of the intelligent pneumatic corset with built-in them are described.

Electromagneticsoft actuator arrays (ESAAs) combine compliance with fast, controllable actuation and scalability, providing a promising foundation for the development of interconnected soft actuator arrays inspired by the structure and function of biological muscles. In this work, we present a control framework and an actuator selection strategy for an artificial soft muscle composed of ESAAs to enable accurate reference tracking. Since directly measuring the states of each ESA is often impractical in real-world applications, we first design a Kalman filter-based observer to estimate all system states from available observations. Using these estimates, we develop a Linear Quadratic Gaussian (LQG) controller to achieve reference tracking. Since thermal buildup from constant use can damage the actuators, we consider whether switching between different subsets of active actuators could offer thermal relief. While actuator switching intuitively suggests reduced heating by providing resting periods, our investigation reveals that this strategy can lead to higher thermal accumulation compared to the continuous mode. This is because we need substantially larger control effort when we have fewer active actuators in the switching mode, which, in the absence of effective active cooling, fail to provide sufficient heat dissipation during operation. Simulation results are presented to demonstrate the effectiveness of the proposed method in achieving the trajectory objective and to explore how switching affects the system’s thermal profile, revealing a trade-off between tracking performance and heat generation.

To provide a stable surgical view in Minimally Invasive Surgery (MIS), it is necessary for a flexible endoscope applied in MIS to have adjustable stiffness to resist different external loads from surrounding organs and tissues. Pneumatic soft actuators are expected to fulfill this role, since they could feed the endoscope with an internal access channel and adjust their stiffness via an antagonistic mechanism. For that purpose, it is essential to estimate the external load. In this study, we proposed a neural network (NN)-based active load-sensing scheme and stiffness adjustment for a soft actuator for MIS support with antagonistic chambers for three degrees of freedom (DoFs) of control. To deal with the influence of the nonlinearity of the soft actuating system and uncertainty of the interaction between the soft actuator and its environment, an environment exploration strategy was studied for improving the robustness of sensing. Moreover, a NN-based inverse dynamics model for controlling the stiffness of the soft actuator with different flexible endoscopes was proposed too. The results showed that the exploration strategy with different sequence lengths improved the estimation accuracy of external loads in different conditions. The proposed method for external load exploration and inverse dynamics model could be used for in-depth studies of stiffness control of soft actuators for MIS support.