In situ pixel-scale magnetic programming 3D printing technology, pioneering a new era for multifunctional medical applications of soft miniature robots

Research Background

The treatment of gastrointestinal and urinary system diseases has long been plagued by limitations of traditional drug delivery methods, such as low drug concentration at target sites, lack of specificity in release, and short in vivo retention time, all of which result in suboptimal therapeutic efficacy. Magnetic microrobots, with their advantages of non-contact actuation, deep tissue penetration, and non-radiative operation, have emerged as ideal candidates for in vivo targeted drug delivery. However, existing manufacturing methods for magnetic robots have significant drawbacks: mold-assisted pre-deforming magnetization methods struggle to achieve complex deformations; emerging customizable fabrication techniques, such as nozzle magnetization during direct ink writing and laser-induced local remagnetization, can control the remnant magnetization of robot components to a certain extent but lack uniform and high-precision 3D magnetic fields, limiting the functional complexity and deformation accuracy of magnetic robots. To address these limitations, this study developed in-situ pixel-scale magnetic programming 3D printing technology, aiming to break through the bottlenecks of existing manufacturing techniques.

Research Content

1. In-situ Pixel-Scale Magnetic Programming 3D Printing Platform

This platform integrates a 3D uniform magnetic field generator with a mask image projection-based photopolymerization 3D printer. The 3D magnetic field generator consists of two parallelly placed strong NdFeB permanent magnets, which achieve synchronous rotation (rotation angle α) via stepper motors and are entirely mounted on a horizontal rotating plate to generate a horizontal rotation angle γ around the Z-axis, thereby producing a large-scale, uniform programming magnetic field B_Pro(θ,γ). When the magnets rotate from α = 0° to 360°, the generated magnetic field rotates in the opposite direction accordingly, with its angle θ changing from 0° to 360°. Combined with the horizontal rotation angle γ, precise 3D control of the programming magnetic field can be realized. The printing material is a photocurable resin uniformly mixed with pre-magnetized NdFeB microparticles. During the printing process, the programming magnetic field is first adjusted to a specified direction by the generator, aligning the magnetic particles in the precursor resin along this direction. Subsequently, a UV mask image is projected to cure selected pixels, thus locking the alignment direction of the magnetic particles. By repeating this process, the remanent magnetization direction of each pixel can be individually programmed, and after layer-by-layer curing, a 3D structure with pixel-scale magnetic programming is finally obtained. The 3D programming magnetic field generated by this platform exhibits excellent strength and uniformity, with an average intensity of 50 mT in a 3 cm×3 cm square area, which is sufficient to meet the requirements of particle alignment during magnetic programming.

The platform integrates a 3D uniform magnetic field generator with a mask image projection-based photopolymerization 3D printer. The printing material is a photocurable resin uniformly mixed with pre-magnetized NdFeB microparticles. During the printing process, the programming magnetic field is first adjusted to a specified direction via the generator, aligning the magnetic particles in the precursor resin accordingly. A UV mask image is then projected to cure selected pixels, locking the orientation of the aligned particles. By repeating this process, the remnant magnetization direction of each pixel can be individually programmed. After sequential layer-by-layer curing, a 3D structure with pixel-level magnetic programming is obtained. The 3D programming magnetic field generated by the platform exhibits excellent strength and uniformity, with an average intensity of 50 mT within a 3 cm×3 cm square area, sufficient to meet the requirements of particle alignment during magnetic programming.

2. Design and Functions of 1D Strip Magnetic Robots

Tailored for the narrow and curved intestinal environment, 1D strip magnetic robots achieve programmable multi-curved deformations under a uniform actuation magnetic field by precisely regulating the θ direction of magnetic moment density in different regions. The proposed key-node splicing magnetization method, based on stress distribution in multi-curved deformations, decomposes complex multi-curves into multiple simple cantilever segments in the X-Z coordinate system. By selecting appropriate cantilever types, rotation rates, and variations in the actuation magnetic field, complex multi-curved shapes can be combined. The 1D strip magnetic robots fabricated using this method exhibit diverse motion modes, such as dolphin-like undulation and beetle-like rolling under a rotating magnetic field, and caterpillar-like forward and backward crawling under a pulsed magnetic field. In excised pig intestines, these robots successfully demonstrated multi-mode locomotion and could carry hydrogel drug patches, releasing the drug upon reaching the target site.

3. Design and Functions of 2D Membrane Magnetic Robots

To adapt to larger enclosed spaces with gas-liquid mixed environments (e.g., the stomach and bladder), 2D membrane magnetic robots with claws were developed. Unlike the in-plane photocuring method used for 1D robots, 2D membrane robots generate precisely controllable twisting deformations by photocuring pixels perpendicular to the γ plane and gradually rotating the θ angle of the programming magnetic field. These 2D membrane robots can achieve various deformations and functions, including rolling, crawling, obstacle crossing, and propulsion. In a stomach model, they can move on ridged surfaces through rolling, clawing, and obstacle-crossing deformations; underwater, they can perform octopus-like swimming and steering under a 4 Hz pulsed magnetic field, with a speed of 0.6 cm/s.

4. Design and Functions of 3D Spiral Capsule Robot

3D spiral capsule robots feature two back-to-back thin-walled cavities and a surrounding screw-thread structure. Using the 3D spatial magnetization technology of the in-situ pixel-scale programming printing platform, the two cavities are oppositely magnetized, enabling independent squash deformations under an external magnetic field. The screw thread is magnetized perpendicular to the magnetization direction of the cavities, allowing independent control of its rotational motion via a rotating magnetic field. In in vivo rabbit experiments, the robot was administered orally, carrying drug droplets to the stomach. Under external magnetic actuation, it achieved multi-mode motions such as spiral propulsion, lateral rolling, and redirection. Upon reaching the target site, precise drug release was triggered via squash deformation under pulsed magnetic fields, and the robot was eventually excreted safely.

Summary

This study successfully fabricated 1D, 2D, and 3D magnetic robots using in-situ pixel-scale magnetic programming 3D printing technology. These robots, with their diverse motion modes and functions, can adapt to different in vivo environments and accomplish complex tasks. Compared with traditional manufacturing techniques, this method integrates voxel-level geometry and magnetization properties into an automated platform, reducing manual labor, improving manufacturing efficiency, and is particularly suitable for fabricating complex 3D magnetically responsive robots. In the future, by further improving the precision of magnetic programming profiles and structures, optimizing biocompatibility, and enhancing the scalability of manufacturing methods, this technology is expected to drive significant breakthroughs in related fields and bring more innovative applications to the medical field.

Professor Huawei Chen from the School of Mechanical Engineering and Automation, Beihang University, is the corresponding author of the paper. Doctoral student Song Zhao and Associate Professor Liwen Zhang are the co-first authors. Beihang University is the first and corresponding institution. This research was supported by the National Key Research and Development Program of China (No. 2025YFC3408703), the National Natural Science Foundation of China (Nos. U2441273, T2121003), the XPLORER PRIZE, and the Fundamental Research Funds for the Central Universities.

Sources: https://spj.science.org/doi/10.34133/research.0734