Smart mechanical metamaterials based on various types of stimuli-sensitive materials break through the limitations of traditional metamaterials and exhibit many attractive properties. The development of multi-functional mechanical metamaterials capable of multi-mode, reversible, large deformations and remote controllability remains a challenge. In this work, we designed and prepared several magneto-mechanical metamaterial unit cells based on magnetoactive soft materials using 3D printing technology. A novel cell structure of cuboctahedron was fabricated and examined deeply which was elongated or contracted along the central magnetic field direction under different external magnetic fields. Experiment and simulation results shown that the special metamaterial structure design enables the magneto-active unit cells to achieve super deformation characteristics that it does not originally possess. The rapid two-way large deformation of the cuboctahedron cell was achieved with a quite remarkable deformation up to 85%, and it could quickly return to the original shape of the cell when the magnetic field was removed. Besides of these capabilities, as an application example, we further demonstrated the multi-modal shape of shrinkage and elongation of the cell structure in a biomimetic blood vessel, to show the effectiveness of the prototype smart stent for particle transport in a remotely controllable manner. The developed magneto-mechanical metamaterial certainly can be extended to various functionalized application, such as soft robots, healthcare and flexible electronics.

Magneto-active soft materials fabricated by new paradigms of 3D printing have received considerable interest for various applications owing to their remarkable complex deformation and extraordinary magneto-mechanical properties. The morphology and magneto-mechanical properties of materials prepared by direct ink writing (DIW) 3D printing, on the other hand, are closely related to process and material parameters that are critical in this printing technique. In this study, the morphology of ink filaments printed under different parameters was investigated through theoretical analysis and experimental tests to achieve the implementation. The results demonstrated that the prepared magnetic inks are suitable for DIW, and the predictions based on a simplified hydrodynamic model are basically consistent with the measured data in the experiments. It also showed that the diameter of the extruded ink filaments increases with increasing extrusion pressure, and decreasing printing speed, layer height, and magnetic particle content. Similarly, the magnetic property varies with the nozzle diameter and material composition variations. Using the obtained optimal parameters, several magneto-active rods and plate-like structures with a specific arrangement of microscopic magnetic domains were successfully fabricated. Their magnetically driven behavior further was investigated experimentally and numerically, which revealed a programmed, non-contact remote control, reversible, and multimodal large deformation characteristics. The findings of this study allow a more in-depth understanding and analysis of processing-structure-property correlations of printed magneto-active soft materials, laying the groundwork for personalized customization and versatile development of magneto-mechanical performance.

Improving the performance of flexible eddy current (EC) probes (FECPs) is a current research hotspot. Thus, a novel FECP, fractal EC sensor technology is proposed. This FECP can enhance the consistency of the probe for detecting short cracks in different orientations by changing the coil structure of the probe, thereby reducing the probability of missing the particular direction cracks. However, due to the limit of the wires’ layout space, an issue remains: the fractal probe’s signal output is weak. To break through this limitation, this study proposes a method to achieve the passive amplification of the output signal of FECPs. A layer of homemade flexible sheet doped with pure iron particles is covered on a flexible Koch differential pick-up fractal EC probe. First, the manufacturing details of the flexible sheet and probe are provided; then, the influence of the probes with and without sheet on the amplification of the crack detection signals is compared via finite element analysis and experiment. The results show that the probe with the sheet can realize the passive amplification to the crack signals in C-scan experimental results of 28 kinds of cracks, and under the excitation frequencies of 50, 100, and 1000 kHz, the signal amplitudes output from the probe with sheet increase by at least 12.8%, 27.6%, and 40.4%, respectively.