3D-Printed Magnetic Soft Robots Change Shape Mid-Movement on Command

Soft robots have long promised the kind of adaptable, muscle-like movement that rigid machines cannot match, but most of them can only ever walk, grip, or swim in the single way their designers gave them. A new study published in Advanced Composites and Hybrid Materials changes that calculus. A team led by researchers at Jilin University, working with colleagues at the Liaoning Academy of Materials and the University of Oxford, has fabricated a magnetically actuated soft robot that can reshape its own body while it is still moving, and then lock into the new configuration and carry on in a completely different gait. The robot crawls, rolls, and jumps, and it decides which mode to use not through a mechanical gearbox but through nothing more than carefully choreographed magnetic fields applied from outside the body.

The enabling technology is direct ink writing, an extrusion-based form of 3D printing in which a viscous ink is pushed through a fine nozzle along programmable toolpaths, building up complex three-dimensional structures layer by layer. What makes this work distinctive is not the printer itself but the inks. The researchers formulated soft polymer matrices loaded with two kinds of functional magnetic particles. Neodymium-iron-boron, or NdFeB, particles provide the strong, permanent magnetization that lets an external field push and pull on the robot’s limbs. Iron oxide, Fe3O4, particles play a subtler role: they concentrate heat locally when the material is exposed to a rapidly oscillating magnetic field. By printing these two particle-laden inks alongside plain soft polymer into a single monolithic architecture, the team created a robot in which actuation, heating, and structural compliance are distributed exactly where they are needed.

The cleverness of the design lies in how the two particle systems divide the labor. When a high-frequency magnetic field is applied, the Fe3O4 particles act as microscopic heaters, warming only the regions where they were printed. Those regions are made of shape memory polymers, materials that soften dramatically above a transition temperature and then stiffen again on cooling, remembering whatever shape they were molded into while soft. By selectively heating different zones of the robot, the operators can temporarily reduce the stiffness of specific parts of the body, allowing the low-frequency magnetic field that simultaneously drives the NdFeB-rich segments to fold or twist the robot into a new geometry. Once the high-frequency field is switched off, the shape memory polymer cools and hardens, locking the new shape in place without any continuous power input.

This combination of on-demand softening and magnetic reshaping is what the authors describe as on-the-fly shape morphing, and the phrase is meant literally. The robot does not need to stop, be picked up, or be reprogrammed between modes. While it is mid-crawl, an operator can ramp up the high-frequency field, watch a segment of the body go limp and refold under the steering field, then drop the frequency and the robot resumes locomotion in its new configuration, for example switching from a crawling posture suited to squeezing through a narrow channel to a compact rolling form suited to open ground. Because the entire body is one printed piece, there are no hinges, screws, or assemblies to fail, and the shape transition is reversible and repeatable.

Demonstrating robust locomotion was a central part of the study. The team showed the robot transitioning among at least three distinct gaits: crawling, in which the body deforms cyclically to generate friction-anchored forward motion; rolling, in which the locked body shape lets the field tumble the robot efficiently across flat terrain; and jumping, in which stored elastic energy is released in a rapid burst to hop over obstacles. Each mode places different demands on the body’s stiffness and geometry, which is precisely why the ability to reconfigure matters. A robot locked into a crawler’s elongated profile cannot roll well, and a roller cannot leap. The printed architecture lets one physical object embody all three, selected in real time by external fields alone.

The researchers also demonstrated environmental adaptation and targeted load-bearing delivery, pushing the robot across multiple terrain types and showing that it could carry a payload to a designated location. This is where the work connects to some of the most pressing applications in soft robotics. Machines that must operate in unstructured and confined environments, such as the inside of industrial piping, disaster rubble, or the digestive tract, face constantly changing conditions. A rigid robot tuned for one environment fails in another. A soft robot that can flatten to pass a constriction, then roll briskly across an open chamber, then hop over a lip, addresses that variability with a single, untethered platform driven only by fields that penetrate deeply into the body without wires or batteries.

The significance of the non-contact aspect deserves emphasis. Many shape-changing robots rely on embedded heaters, pneumatic channels, or cables to trigger reconfiguration, all of which require either tethering to external equipment or complex onboard hardware. The Jilin-led team’s approach uses only magnetic fields, which pass through the material without physical connection. High-frequency fields for heating and low-frequency fields for actuation can be generated by external coil systems, meaning the robot itself carries no electronics at all. That simplicity translates into durability and miniaturization potential, since there is nothing onboard to break, seal, or power, and it opens a path toward robots small enough for biomedical use where batteries and wiring are impractical.

From a materials science standpoint, the study also showcases how direct ink writing expands design freedom in soft robotics. Conventional soft robot fabrication, often based on molding and soft lithography, struggles to place multiple functional materials with fine spatial control inside a single compliant body. Extrusion printing solves this by letting the designer choose, voxel by voxel along each printed line, whether a given region is elastic, magnetically responsive, or heat-generating, and how the magnetization directions and particle concentrations are graded across the structure. The result is a dual polymer matrix architecture in which mechanics and function are co-designed, a philosophy increasingly seen as the future of multifunctional soft machines. The monolithic multi-material body also avoids delamination failure modes that plague glued or bonded assemblies of dissimilar soft materials.

The work was carried out at the Key Laboratory of Bionic Engineering of the Ministry of Education at Jilin University, with Yumeng Han, Lu Zhang, and Xueli Zhou contributing equally as lead authors, alongside Qingping Liu, Luquan Ren, Chao Xu, and Liang He of the Institute of Biomedical Engineering at the University of Oxford. The research was supported by the National Natural Science Foundation of China, the Department of Science and Technology of Jilin Province, and the 10th CAST Young Elite Scientists Sponsorship Program. The team reports no competing interests, and the article is published open access, with extensive supplementary video material documenting the robot’s crawling, rolling, jumping, and payload-carrying maneuvers.

What comes next is the question that inevitably follows a demonstration like this. The dual-field magnetic strategy scales conceptually to smaller length scales, where magnetic actuation is already the method of choice for millimeter-scale medical robots, and the shape memory locking mechanism solves one of the field’s chronic problems, which is that soft robots typically need continuous field input merely to hold a pose. If future versions can reconfigure among even more modes, sense their surroundings, and do so at clinical scales, the printed morphing body demonstrated here could become a blueprint for a generation of untethered machines that change their bodies the way animals do, adapting their form to the task at hand while never stopping to make the change.

Subject of Research: Direct ink writing of multi-material soft polymer matrices for magnetically actuated, shape-morphing soft robots

Article Title: Direct ink writing of soft polymer matrices enables on-the-fly shape morphing in soft robots

Article References: Han, Y., Zhang, L., Zhou, X., Liu, Q., Ren, L., Xu, C., & He, L. (2026). Direct ink writing of soft polymer matrices enables on-the-fly shape morphing in soft robots. Advanced Composites and Hybrid Materials. https://doi.org/10.1007/s42114-026-02078-x

Image Credits: AI Generated

DOI: 10.1007/s42114-026-02078-x

Keywords: soft robotics, direct ink writing, shape memory polymers, magnetic actuation, NdFeB particles, Fe3O4 particles, shape morphing, dual magnetic fields, multi-material 3D printing, locomotion modes, bioinspired robotics, smart materials