3D-Printed Magnetic Soft Robots Take Shape With In-Process Magnetization

Researchers have unveiled a 3D printing strategy that magnetizes soft materials while they are being printed, allowing engineers to program complex magnetic profiles directly into three-dimensional structures. The approach, detailed in Advanced Science, combines multi-material direct ink writing with a freely moving external magnet that is translated in three dimensions and rotated about two axes during fabrication. By applying magnetization after each printed layer, the team achieved fully three-dimensional magnetization profiles in elastomer composites containing neodymium-iron-boron microparticles, overcoming long-standing limitations of post-process and print-direction-based magnetization methods.

Conventional approaches have struggled to deliver both complex 3D geometries and arbitrary magnetization simultaneously. Uniform post-process magnetization with strong impulse fields produces only one-dimensional profiles, while techniques that deform and fix structures before magnetizing are restricted to thin, simple shapes. Direct ink writing with fields applied at the printing tip confines magnetization to the print path, making out-of-plane magnetization of curved shells difficult. Free magnets positioned beneath the substrate lose strength with height, limiting designs to flat geometries such as hinges. The new method sidesteps these constraints by positioning the magnet above the print and synchronizing magnetization with curing kinetics.

The researchers characterized the magnetic, rheological, and mechanical properties of their NdFeB-silicone composites across particle loadings of 10 to 50 weight percent. Coercivity remained essentially constant with increasing particle content, while saturation magnetization rose, allowing designers to tune magnetic response without stronger actuating fields. A 40 weight percent formulation was selected to maximize magnetic output while preserving print resolution of roughly 50 to 100 micrometers and material flexibility near 10 megapascals. Curing experiments at temperatures from 40 to 70 degrees Celsius revealed that a bed temperature of 60 degrees Celsius, yielding a nine-minute cure, best aligned cross-linking with the magnetization time scale.

A key finding is that magnetizing the composite before full curing produces stronger net magnetization than magnetizing after cross-linking. Hysteresis measurements during curing showed that magnetic domains align more readily in low-viscosity, uncured material. Thin composites magnetized prior to curing exhibited significantly larger bending angles under an external field than identical samples magnetized three hours later. Cylindrical samples magnetized from above between layers showed top-surface magnetic fields approximately 6.2 times greater than those magnetized conventionally from below, because the magnet-to-layer distance stayed constant throughout fabrication.

Bringing a magnet close to uncured, low-viscosity elastomer risks deforming the material, so the team carefully parameterized the process. They measured the minimum distance at which droplets of varying sizes remain stable without jumping toward the magnet and found that jumping propensity decreases sharply as curing progresses; after 150 seconds at 50 degrees Celsius, jumping distance fell by 76 percent. Theoretical models of bulk fluid jumping, particle migration, and particle rotation, combined with finite element analysis and X-ray fluorescence and micro-CT imaging, confirmed that magnetization under optimized conditions arises primarily from rotational alignment of particles and their magnetic domains rather than from particle migration or bulk deformation.

With the process optimized, the researchers demonstrated discretely magnetized structures, including thin strips magnetized in two regions with different directions, producing distinct bending patterns that matched finite element predictions. A cubic shell magnetized with each face oriented normal to its surface underwent competing wall deformations under external fields applied along different axes. The team also printed magnetized cubes and flexible meshes that functioned as strain sensors: compression, tension, and bending each produced measurable changes in stray magnetic fields detected by a three-axis Hall sensor, with stable responses over 2000 cycles. A flexible keycard containing sixteen independently magnetized pixels generated unique field signatures that triggered distinct LED patterns, illustrating contactless magnetic identification.

Continuous magnetization profiles were achieved by sweeping a rotating magnet along strips during curing. A single full rotation produced a strip with a single central attractive bulge, while 1.5 rotations created simultaneous regions of attraction and repulsion at one-third and two-thirds of the strip length. Hall sensor scans of the magnetization profiles closely matched simulations. Applying the same principle to a planar flower with radially symmetric quarter-rotation magnetization per petal produced S-shaped folding under an external field, a bending pattern unattainable with uniform magnetization.

Biologically inspired demonstrators highlighted the platform’s versatility. A two-centimeter dragonfly with oppositely magnetized wings flapped with maximum arc length near a 7-hertz resonant driving frequency, with finite element analysis predicting resonant modes of about 6.83 and 6.32 hertz for the front and rear wings. A neutrally buoyant robotic octopus with eight continuously magnetized arms swam vertically at up to 10.4 millimeters per second near a 4-hertz resonance in a weak 1 to 10 millitesla alternating field, and glided laterally across the water surface at 17.4 millimeters per second under a 2-millitesla static field, using a trapped air bubble for buoyancy.

The most application-oriented demonstration was a hollow serpentine catheter, 20 centimeters long, with six discrete magnetic nodes each offering two rotational degrees of freedom. Because the structure is hollow, multi-material, non-planar, and requires magnetization along the cylinder axis, it could not be fabricated by molding, print-direction magnetization, or substrate-mounted magnets. In a mock bifurcated tissue environment, the catheter was steered magnetically through tortuous pathways while self-lubricating with dyed fluid and delivering a red-dye payload to a target, mimicking minimally invasive drug delivery compatible with robotic magnetic navigation systems used clinically.

The authors note that they deliberately avoided a strong saturating pre-treatment field to isolate the effect of rotational alignment with a small cylindrical magnet, and that synergy between pre-treatment and in-process magnetization remains to be explored. Nonetheless, the framework establishes a robust route to soft, magnetically controlled actuators and sensors with tunable, programmable behaviors, opening possibilities for soft robotics, adaptive structures, shape-morphing devices, and biologically inspired magnetic systems.

Subject of Research: In-process magnetization during 3D printing of magnetorheological elastomers for heterogeneous magnetic profiles and anisotropic actuation

Article Title: In‐Process Magnetization for 3D Printing of Magnetorheological Elastomer with Heterogeneous Magnetic Profile for Anisotropic Actuation

Article References: Glass, P., Hassouna, D., Epitawala Arachchige, U., Jeong, H. Y., Park, S. H., & Joung, D. (2026). In‐Process Magnetization for 3D Printing of Magnetorheological Elastomer with Heterogeneous Magnetic Profile for Anisotropic Actuation. Advanced Science, 13(50), Article e76045. https://doi.org/10.1002/advs.76045

Image Credits: AI Generated

DOI: 10.1002/advs.76045

Keywords: 3D printing, magnetorheological elastomer, in-process magnetization, soft robotics, NdFeB composites, anisotropic actuation, Hall sensor sensing, bioinspired robots, serpentine catheter, direct ink writing, magnetic domains, programmable magnetization