Magnetoactive microlattice metamaterials with highly tunable stiffness and fast response rate

Active metamaterials with shapes or mechanical properties that can be controlled remotely are promising candidates for soft robots, flexible electronics, and medical applications. However, current active metamaterials often have long response times and short ranges of linear working strains. Here, we demonstrate magnetoactive microlattice metamaterials constructed from 3D-printed, ultra-flexible polymer shells filled with magnetorheological (MR) fluid. Under compressive stress, the magnetorheological fluid develops hydrostatic pressure, allowing for a linear compression strain of more than 30% without buckling. We further show that under a relatively low magnetic field strength (approximately 60 mT), the microlattices can become approximately 200% stiffer than those in a relaxed state, and the energy absorption increases ~16 times. Furthermore, our microlattices showed an ultra-low response time with “field on” and “field off” times of ~200 ms and ~50 ms, respectively. The ability to continuously tune the mechanical properties of these materials in real time make it possible to modulate stress‒strain behavior on demand. Our study provides a new route toward large-scale, highly tunable, and remotely controllable metamaterials with potential applications in wearable exoskeletons, tactile sensors, and medical supports. A liquid–solid dual-phase magnetoactive microlattice metamaterial composed of flexible 3D-printed polymer shell and magnetorheological (MR) fluid has been designed and fabricated. The MR fluid-filled magnetoactive microlattices demonstrated remarkable recoverability (~50%) and be substantially stiffened in the presence of a magnetic field, with an ~200% increment in stiffness at 60 mT. Based on specific applications, the mechanical properties of this magnetoactive microlattice metamaterial can be modulated on demand, leading to certain programmable stress-strain behavior.