Programmable soft electrothermal actuators based on free-form printing of the embedded heater

Design of a Bistable Artificial Venus Flytrap Actuated by Low Pressure with Larger Capture Range and Faster Responsiveness

The rapid closure of the Venus flytrap (Dionaea muscipula) can be completed within 0.1-0.5 s due to the bistability of hyperbolic leaves and the curvature change of midrib. Inspired by its bistable behavior, this paper presents a novel bioinspired pneumatic artificial Venus flytrap (AVFT), which can achieve a larger capture range and faster closure action at low working pressure and low energy consumption. Soft fiber-reinforced bending actuators are inflated to move artificial leaves and artificial midrib fabricated from bistable antisymmetric laminated carbon fiber-reinforced prepreg (CFRP) structures, and then the AVFT is rapidly closed. A two-parameter theoretical model is used to prove the bistability of the selected antisymmetric laminated CFRP structure, and analyze the factors affecting the curvature in the second stable state. Two physical quantities, critical trigger force and tip force, are introduced to associate the artificial leaf/midrib with the soft actuator. A dimension optimization framework for soft actuators is developed to reduce their working pressures. The results show that the closure range of the AVFT is extended to 180°, and the snap time is shortened to 52 ms by introducing the artificial midrib. The potential application of the AVFT for grasping objects is also shown. This research can provide a new paradigm for the study of biomimetic structures.

Magnetically controlled bio-inspired elastomeric actuators with high mechanical energy storage

Many biological systems are made to operate more quickly, efficiently, and with more power by storing elastic energy. This work introduces a straightforward bioinspired design for the quick manufacture of pre-stressed soft magnetic actuators. The actuator requires a lower magnetic field strength to be activated and can regain its original shape without the need for external stimuli. These characteristics are demonstrated in this work through the creation of actuators with round and helical shape structures inspired by the tendril plant and chameleon's tongue. Both the final form of the actuator and its actuation sequence may be programmed by controlling the direction and strength of the force utilised to pre-stress the elastomeric layer. Analytical models are presented to trace the actuators' energy storage, radius, and pitch. High-speed shape recovery after releasing the magnetic force and a strong grasping force are achieved due to the stored mechanical elastic energy. Experiments are conducted to analyse the shape changes, grasping action, and determine the actuation force. The manufacture of the grippers with zero-magnetic field strength holding capacities of up to 20 times their weight is made possible by the elastic energy that actuators store in their pre-stressed elastomeric layer. The outcomes of our research show that a unique magnetic field-controlled soft actuator can be created in different shapes and designs based on requirements.

Shape memory meta-laminar jamming actuators fabricated by 4D printing

Laminar jamming (LJ) technology is a hot topic because it allows for the transition from conventionally quick, precise, and high-force rigid robots to flexible, agile, and secure soft robots. This article introduces a novel conceptual design of meta-laminar jamming (MLJ) actuators with a polyurethane shape memory polymer (SMP)-based meta-structure fabricated by 4D printing (4DP). The sustainable MLJ actuators behave as soft/hard robots via hot and cold programming accompanied by negative air pressure. The advantage of MLJ actuators over conventional LJ actuators is that a continuous negative air pressure is not required to stimulate the actuator. SMP meta-structures with circle, rectangle, diamond, and auxetic shapes are 4D printed. Mechanical properties of the structures are evaluated through three-point bending and compression tests. Shape memory effects (SMEs) and shape recovery of meta-structures and MLJ actuators are investigated via hot air programming. MLJ actuators with auxetic meta-structure cores show a better performance in terms of contraction and bending with 100% shape recovery after stimulation. The sustainable MLJ actuators have the capabilities of shape recovery and shape locking with zero input power while holding 200 g weight. The actuator can easily lift and hold objects of varying weights and shapes without requiring any power input. This actuator has demonstrated its versatility in potential applications, such as functioning as an end-effector and a gripper device.

Multi-stimuli-responsive actuator based on bilayered thermoplastic film

Recently, soft actuators have attracted considerable interest owing to their biomimetic performance. Unfortunately, it remains a great challenge to fabricate multi-stimuli-responsive soft actuators by a facile but low-cost method. Herein, a thermoplastic film with bilayered architecture was designed and fabricated by a one-step method. This bilayered thermoplastic film can act as a soft actuator, demonstrating versatile shape-programmable performance in response to acetone vapor exposure and temperature change. Interestingly, diverse biomimetic devices including a worm-like self-walker, crawler-type robot and soft gripper can be realized, which highlights its promising applications in biomimetic robots, artificial muscles and automatic devices. Considering the one-step preparation process and the low-cost raw materials, this approach can be cost-effectively scaled up for practical production.

Light-driven untethered soft actuators based on biomimetic microstructure arrays

Soft actuators based on smart materials and structures that can perform more diverse tasks skillfully, are being intensively sought. Despite the good progress made in the past few years, locomotion and transportation functionalities of the untethered soft-bodied devices for various natural terrains remain challenging. Inspired by a gecko crawling system, an untethered soft actuator with the abilities of picking up, transporting, and delivering objects controlled by NIR light is proposed. The soft actuator consisting of photo-responsive MWCNTs units and mushroom shaped microstructures, was fabricated by an integrative soft-lithography method with inking and imprinting processes. The integrated MWCNTs unit can convert NIR light irradiation into thermal energy, which can make the body of the soft actuator generate a strong shape deformation intrinsically in a self-contained way, leading to a combined discontinuous and continuous locomotion. Moreover, the integrated mushroom shaped microstructures can also realize grasping and manipulation of the object that was not constrained by the object's shapes and sizes, which was further addressed from experimental and theoretical perspectives. Thus, the combined use of smart materials and structures opens up new research avenues and represents a step forward toward future applications of light-driven untethered soft actuators.