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

Soft magneto‐responsive shape memory foam composite actuators

Soft magnetic composites are exceptional because they can be controlled remotely, move quickly, conform to hard things, and interact with people safely. However, even with all these features, magnetic elastomers suffer a lack of stability due to the high softness of the elastomer. This issue affects their controllability and repeatability. This article introduces a novel conceptual design of magneto-responsive shape memory polyurethane (SMP) foam composites with high stability and reversibility. The fabrication technique is based on the silicone resins filled with strontium ferrite magnetic particles and a thin SMP foam placed onto one side. Material properties, room-temperature shape recovery features, and magnetization conditions necessary for the process are determined by experimental studies of composite actuators. As a result, a workable, light, stable, soft composite gripper with programmable magnetic patterns is created, which can carry out activities like grabbing, holding, and moving objects in horizontal and vertical directions when a low magnetic field is applied. The SMP foam increases the contact surface and decreases the weight by up to three times providing better stability compared to the magnetic elastomer without SMP foam. The shape-recoverable gripper with a small contract area can lift objects eight times heavier than its weight

Sustainable 4D printing of magneto-electroactive shape memory polymer composites

Typical techniques for creating synthetic morphing structures suffer from a compromise between quick shape change and geometric complexity. A novel approach is proposed for encoding numerous shapes and forms by magneto-electroactive shape memory polymer composite (SMPC) structures and integrating sustainability with 4D printing (4DP) technology. Electrically driven, remote controllability, and quick reaction are the features of these sustainable composite structures. Low-cost 4D-printed SMPC structures can be programmed remotely at high temperatures to achieve multi-stable shapes and can snap repeatedly between all programmed temporary and permanent configurations. This allows for multiple designs in a single structure without wasting material. The strategy is based on a knowledge of SMPC mechanics, magnetic response, and the manufacturing idea underlying fused deposition modelling (FDM). Iron-filled magnetic polylactic acid (MPLA) and carbon black-filled conductive PLA (CPLA) composite materials are investigated in terms of microstructure properties, composite interface, and mechanical properties. Characterisation studies are carried out to identify how to control the structure with a low magnetic field. The shape morphing of magneto-electroactive SMPC structures is studied. FDM is used to 4D print MPLA and CPLA adaptive structures with 1D/2D-to-2D/3D shapeshifting by the magnetic field. The benefits of switchable multi-stable structures are reducing material waste and effort/energy and increasing efficiency in sectors such as packaging

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

Magnetorheological elastomer‐based 4D printed electroactive composite actuators

Magnetorheological elastomer (MRE) composite actuators are extraordinary since they can be controlled remotely, move swiftly, adapt to rough surfaces, and engage with humans in a secure manner. Despite all these advantages, pure MREs are not stable enough because of their high degree of softness. Also, a magnetic field is always required to actuate and hold them in the required position accordingly. This paper offers a new conceptual design for bi-stable MRE-based electroactive composite actuators with high performance. The idea is a combination of MRE composites and 4D printing (4DP) of conductive shape memory polymers. The silicone resins are loaded with strontium ferrite magnetic particles and a thin conductive carbon black polylactic acid (CPLA) is 4D printed and embedded as a core inside the composite. A set of parametric studies is carried out to examine the material properties, 4DP characteristics, and magnetization conditions. As an outcome, a functional, lightweight, and bi-stable composite actuator with programmable magnetic patterns is developed. This actuator can be positioned in the actuated situation without any stimuli as long as required. The shape memory behaviour, bi-directionality, and remote controlling of the composite actuator are driven by Joule heating and magnetic fields. The actuator with a weight of 1.47 g can hold and lift weights up to 200 g. Finally, experiments are conducted to demonstrate the immense potential of the developed composite actuators as mechanical and biomedical devices. Due to the absence of similar concepts and results in the specialized literature, this paper is likely to advance the state-of-the-art smart composite actuators with remotely controlled shape-memory features

4D printing and programming of continuous fibre-reinforced shape memory polymer composites

This study demonstrates the use of fused filament fabrication (FFF) 4D printing (4DP) to print programmable continuous fibre-reinforced composite (CFRC) structures with exceptional strength and eco-friendly features. This research focuses on bio-shape memory polymer composites (SMPCs) and employs experiments to fabricate lightweight CFRC parts using FFF technology. Different types of continuous fibres, including carbon fibre (CF), aramid fibre (AF), and fibreglass (FG), are incorporated into a biopolymer matrix made of biodegradable polylactic acid (PLA). The study evaluates microstructure, mechanical properties, and shape memory properties of SMPCs, employing techniques like cold and hot programming. Continuous fibres significantly enhance mechanical properties, increasing strength by over 1027.5 % in tensile tests and nearly 497.3 % in three-point bending tests. The research also addresses shape recovery and fixity ratios in 4D-printed SMPCs, finding a decrease when continuous fibres are incorporated into PLA. Notably, FGPLA specimens achieve the highest shape recovery ratio of approximately 95 ± 1 % after pure PLA. These findings highlight the potential of 4D-printed CFRCs in various applications, from human-material interaction to mechanical and biomedical fields. They contribute to sustainability by reducing material consumption and waste, demonstrated through the creation of reusable and lightweight items like hooks, lockers, finger splints, and meta-composites

Soft pneumatic actuators with controllable stiffness by bio‐inspired lattice chambers and fused deposition modeling 3D printing

This article shows how changing 3D printing parameters and using bio-inspired lattice chambers can engineer soft pneumatic actuators (SPAs) with different behaviors in terms of controlling tip deflection and tip force using the same input air pressure. Fused deposition modeling (FDM) is employed to 3D print soft pneumatic actuators using varioShore thermoplastic polyurethane (TPU) materials with a foaming agent. The effects of material flow and nozzle temperature parameters on the material properties and stiffness are investigated. Auxetic, columns, face-centered cubic, honeycomb, isotruss, oct vertex centroid, and square honeycomb lattices are designed to study actuators’ behaviors under the same input pressure. Finite-element simulations based on the nonlinear hyper-elastic constitutive model are carried out to precisely predict the behavior, deformation, and tip force of the actuators. A closed-loop pneumatic system and sensors are developed to control the actuators. Results show that lattice designs can control the bending angle and generated force of actuators. Also, the lattices increase the ultimate strength by controlling the contact area inside the chambers. They demonstrate variable stiffness behaviors and deflections under the same pressure between 100 and 500 kPa. The proposed actuators could be instrumental in designing wearable hand rehabilitative devices that assist customized finger and wrist flexion-extension

Porcospino Flex: a bio-inspired single-track robot with a 3D-printed, flexible, compliant vertebral column

This paper is focused on the design and development of the Porcospino Flex, a single-track robot inspired by nature and featuring a meta-material structure. In the earlier version of the Porcospino, the main body was composed of a chain of vertebrae and two end sections linked by flexible joints, but the excessive use of materials in 3D printing and the resulting weight of the robot posed challenges, ultimately leading to a decrease in its overall efficiency and performance. The Porcospino Flex is manufactured through the fused deposition modeling process using acrylonitrile butadiene styrene and thermoplastic polyurethane, featuring a singular meta-material structure vertebral column. The adoption of a lattice structure in the main body of the Porcospino Flex leads to a substantial increase in performance, reducing its weight from 4200 g to 3600 g. Furthermore, the decrease in weight leads to a reduction in material usage and waste, making a substantial contribution to the sustainability of the robot. The discussion focuses on the testing results of the Porcospino Flex prototype, highlighting the enhancements observed compared to its prior version

Influence of infill patterns generated by CAD and FDM 3D printer on surface roughness and tensile strength properties

Fused deposition modeling (FDM) is a capable technology based on a wide range of parameters. The goal of this study is to make a comparison between infill pattern and infill density generated by computer-aided design (CAD) and FDM. Grid, triangle, zigzag, and concentric patterns with various densities following the same structure of the FDM machine were designed by CAD software (CATIA V5®). Polylactic acid (PLA) material was assigned for both procedures. Surface roughness (SR) and tensile strength analysis were conducted to examine their effects on dog-bone samples. Also, a finite element analysis (FEA) was done on CAD specimens to find out the differences between printing and simulation processes. Results illustrated that CAD specimens had a better surface texture compared to the FDM machine while tensile tests showed patterns generated by FDM were stronger in terms of strength and stiffness. In this study, samples with concentric patterns had the lowest average SR (Ra) while zigzag was the worst with the value of 6.27 µm. Also, the highest strength was obtained for concentric and grid samples in both CAD and FDM procedures. These techniques can be useful in producing highly complex sandwich structures, bone scaffolds, and various combined patterns to achieve an optimal condition

3D‐printed soft and hard meta‐structures with supreme energy absorption and dissipation capacities in cyclic loading conditions

The main objective of this article is to introduce novel 3D bio-inspired auxetic meta-structures printed with soft/hard polymers for energy absorption/dissipation applications under single and cyclic loading–unloading. Meta-structures are developed based on understanding the hyper-elastic feature of thermoplastic polyurethane (TPU) polymers, elastoplastic behavior of polyamide 12 (PA 12), and snowflake inspired design, derived from theory and experiments. The 3D meta-structures are fabricated by multi-jet fusion 3D printing technology. The feasibility and mechanical performance of different meta-structures are assessed experimentally and numerically. Computational finite element models (FEMs) for the meta-structures are developed and verified by the experiments. Mechanical compression tests on TPU auxetics show unique features like large recoverable deformations, stress softening, mechanical hysteresis characterized by non-coincident compressive loading–unloading curve, Mullins effect, cyclic stress softening, and high energy absorption/dissipation capacity. Mechanical testing on PA 12 meta-structures also reveals their elastoplastic behavior with residual strains and high energy absorption/dissipation performance. It is shown that the developed FEMs can replicate the main features observed in the experiments with a high accuracy. The material-structural model, conceptual design, and results are expected to be instrumental in 3D printing tunable soft and hard meta-devices with high energy absorption/dissipation features for applications like lightweight drones and unmanned aerial vehicles (UAVs)