Magnetic Arthropod Millirobots Fabricated by 3D‐Printed Hydrogels

Abstract

Magnetoactive small-scale soft robots have wide applications in minimally invasive medicine, [1] targeted cargo delivery, [2] and biomedical engineering, [3] because of their prominent ability in swift locomotion, fast response, and remote control. [4] Recently, hard-magnetic soft robots have realized complex deformations. [5] The interactions between the external magnetic field and the programmed magnetic domains of the materials induce body torques, leading to the deformation of the structure to align the magnetization with the external magnetic field. [6] Bending is a basic deformation mode for these shape-transforming structures. However, the homogeneous bending of the whole structure is not energy efficient, with every volume element deforming and storing energy. [7] A design strategy is needed to improve the performance of the magnetic soft robots.For actuation, generating a large folding angle locally is always easier and more energy efficient than homogeneous bending. A successful example can be found in nature. Arthropod (e.g., crab, shrimp) refers to an invertebrate animal with an exoskeleton, a segmented body, and pairs of jointed appendages. [8] Compared to mollusks (e.g., snail, octopus), arthropods have multiple jointed limbs to perform complex movements. For instance, a snail moves its body by squirming (Figure 1a), while a crab moves faster through the movement of the limbs and can further grab objects with claws (Figure 1b). The crab claw functions through the exquisite structure of the limb joint: the driving force is generated by muscle contraction and transmitted through the joint to open or close the claw (Figure 1c). [8b] The joints connect skeleton systems and enable a large folding angle. Joints are also ubiquitous in more advanced mammals, and are widely used in hard robots nowadays. [9] It would be of great interest to introduce joints into the design of magnetic soft robots.In this article, we have developed a series of bioinspired magnetic arthropod millirobots. The basic deforming element is a magnetic beam with a joint. The joint can turn the bending deformation into folding deformation, with the joint region deforming locally. As shown in Figure 1d, the jointed beam deforms into a V-shape (folding mode) instead of a U-shape (bending mode) for the beam without a joint. Obviously, the strain energy is stored more intensively and locally around the sharp angle in the V-shaped sample. Figure 1e indicates that the folding mode is more energy efficient than the bending mode since less strain energy is required for the folding mode to achieve the same bending angle as the bending mode.Toward biomedical applications, hydrogels are preferable as the matrix material of magnetic robots for their good

Bionic Soft Multimodal Actuators for Fast, Large Deformation under Ultralow Magnetic Conditions

“…To more thoroughly understand the crucial contribution of the crab-inspired three-layer joint structure to the superior performance of the actuator, the simulation results with different gap parameters d and the comparison two-layer joint structure of Ref. [29] are given in Figure 4a. For a fair comparison, all these simulations are based on the same material configuration and overall device size.…”

“…It is worth noting that, unlike the two-layer structure in Ref. [29], the upper and lower layers of the three-layer structure here are both implanted with NdFeB magnetic dipolar arrays, which is indeed an essential trick to modulate the superior threshold effect of the actuator.…”

“…For instance, Sun et al proposed a crab-inspired magnetic millirobot, which can move fast and perform complex locomotion because the movements in the form of jointed limbs can turn homogeneous bending into local folding deformation, which considerably reduces the required driving magnetic field. [29] Meanwhile, many living organisms, such as flytraps, demonstrate fascinating adaptability to surrounding stimuli, which offers fertile inspiration for the design of rapidly responsive robots. [30,31] Very recently, Zhang et al reported a flytrap-inspired robotic gripper with a bistable anti-symmetric structure actuated by a magnetic field.…”

Self-Sustained Collective Motion of Two Joint Liquid Crystal Elastomer Spring Oscillator Powered by Steady Illumination

“…Due to the unique advantages of self-excited oscillation systems, they have broad application prospects in the fields of energy acquisition, sensing with electronic skins [10], soft robotics [11][12][13], medical instruments [14][15][16][17], and motors [18]. The self-excited oscillations are generally based on responsive materials, including liquid crystal elastomers (LCEs) [19,20], dielectric elastomers [21], hydrogels [22][23][24], and ion gels [25,26]. Based on different stimuli-responsive materials and structures, different feedback mechanisms are proposed to realize energy compensation, such as the coupling of chemical reactions and large deformation [25,26], the self-shadowing effect [14,27], the coupling of liquid volatilization, and membrane deformation [28].…”

Thermally Driven Self-Rotation of a Hollow Torus Motor

“…In recent years, based on various stimuli-responsive materials including thermally responsive polymer materials [ 26 , 27 ], liquid crystal elastomers (LCEs) [ 28 , 29 , 30 , 31 ], dielectric elastomer [ 32 , 33 , 34 , 35 ], hydrogels [ 36 , 37 ], and ion gels [ 38 , 39 ], a wealth of self-excited motion modes have been proposed, such as rolling [ 40 , 41 ], vibration [ 24 , 31 , 40 , 41 ], torsion [ 41 , 42 ], stretching and shrinking [ 10 , 40 , 43 ], swinging [ 44 ], buckling [ 45 , 46 ], jumping [ 47 , 48 , 49 ], rotation [ 25 , 28 ], eversion or inversion [ 27 , 50 ], expansion and contraction [ 51 , 52 ], swimming [ 53 ] and even group behavior of several coupled self-excited oscillators [ 54 ]. The self-oscillating system is usually accompanied with damping dissipation, and its motion is a non-equilibrium dissipation process.…”