Magnetic Composites—From Printed Magnetoelectronics to Smart Magnetic Soft Robots

Composites consisting of magnetic fillers in polymers and elastomers enable new types of applications in soft robotics, reconfigurable actuation and sensorics. In particular, soft-bodied robots emerge as the closest synthetic system analogous to living organisms mimicking their mechanical behavior and going beyond in performance. We will introduce lightweight, durable, untethered and ultrafast soft-bodied robots performing large amplitude of deformations at high frequencies of up to 100 Hz and exhibit high specific energy density of 10.8 kJ/m3/mT [1]. Our soft-bodied robots can walk, swim, levitate, and transport cargo being driven using external magnetic fields. This inspires new classes of soft robots that impact biosensorics [2], biological tissue engineering, confined and high-speed mechanical (tissue) manipulation, and serve as working models to study fast biomechanical processes like hydro- and aero- dynamics of fast-moving organisms.<br/>These mechanically active structures are typically designed to work in a specific prior defined parameter range and can malfunction when the conditions are changed. Specifically for magnetic soft robots, the change of the intrinsic magnetic properties due to temperature activations or time relaxation can lead to modifications in the actuation pattern. We present ultrathin and reconfigurable magnetic origami actuators based on a composite consisting of shape memory polymers and magnetic microparticles [3]. Self-sensing is achieved by laminating ultrathin magnetosensitive e-skins [4] on soft origami actuators. The sensor assesses the magnetic state of the actuator (magnetized vs. non-magnetized) and decides on its actuation pattern even before the actual actuation is done experimentally. Furthermore, the sensor enables communication of the actuator with external devices (rotation stage, electromagnets) for self-guided assembly of an initially flat layout and provides the possibility to control the sequentiality and quality of the folding process.<br/>Magnetic composites can be readily used to realise not only actuators but also magnetic field sensors. We demonstrate that printed magnetoelectronics can be stretchable, skin-conformal, capable of detection in low magnetic fields and withstand extreme mechanical deformations [5,6]. We feature the potential of our skin-conformal printable sensors in augmented reality settings, where a sensor-functionalized finger conducts remote and touchless control of virtual objects manageable for scrolling electronic documents and zooming maps under tiny permanent magnet.<br/>Furthermore, we will present high performance dispenser printed magnetic field sensors based on non-magnetic half-metallic bismuth powder [7]. Printed Bi sensors reveal non-saturating large magnetoresistance (LMR) effect, reaching up to 146% resistance change at room temperature at 5 T (&gt;3900% at 20 K at 7 T). The LMR is a fingerprint of topological properties of the band structure of Bi. In this respect, this work constitutes the very first use of topological material properties in printing technologies. Due to their thermal and mechanical stability, the sensors printed on thermoplastic foils can be reformed in a stable three-dimensionally shaped object enabling applications of our technology for in-mold electronics. We demonstrate magnetically controlled interactive devices based on a printed array of sensors, to be used for interactive advertisement, smart wallpapers, and security input panels.<br/><br/>[1] X. Wang et al., Communications Materials 1, 67 (2020).<br/>[2] J. Mystkowska et al., Sensors 21, 7122 (2021).<br/>[3] M. Ha et al., Adv. Mater. 33, 2008751 (2021).<br/>[4] G. S. Canon Bermudez et al., Adv. Funct. Mater. 31, 2007788 (2021).<br/>[5] M. Ha et al., Adv. Mater. 33, 2005521 (2021).<br/>[6] E. S. Oliveros Mata et al., Applied Physics A 127, 280 (2021).<br/>[7] E. S. Oliveros Mata et al., Adv. Mater. Technol. 2200227 (2022).