Recently, Professor Jie Kong, Associate Professor Jin Liang, and their research team from Northwestern Polytechnical University have systematically reviewed the design strategies, printing processes, and application progress of magnetically responsive materials in 4D printing. This study thoroughly analyzes the working principles and performance optimization methods of magnetically responsive shape memory materials, and demonstrates their innovative applications in fields such as biomedical tissue engineering, robotics, and intelligent devices. The relevant work was published in Research under the title "4D Printing of Magnetically Responsive Materials and Their Applications" (Research, 2025, DOI: 10.34133/research.0847).

Review Background
4D printing introduces the "time dimension" based on 3D printing, enabling printed structures to undergo controllable dynamic changes in shape, properties, or functions under external stimuli such as magnetic fields, light, and heat. Among various stimulus-response mechanisms, magnetic actuation has demonstrated tremendous application potential in fields like biomedicine and intelligent robotics due to its unique advantages including non-contact manipulation, deep tissue penetration capability, and ultra-fast response speed (millisecond-scale), thus becoming a research hotspot in the field of 4D printing. However, this field still faces numerous bottlenecks: materials lack re-programmability, printing precision is limited by existing additive manufacturing equipment, the capability to fabricate complex structures is insufficient, and the types of printable materials are scarce. With the advancement of nanocomposite technology and 3D printing processes, these drawbacks are being gradually overcome, promoting the expansion of magnetically responsive 4D printing technology into multi-disciplinary cross-field applications.

Review Content
(1) 4D Printing Technology System
This study focuses on analyzing the applicability of four mainstream printing technologies, including Direct Ink Writing (DIW), vat photopolymerization (SLA/DLP), Selective Laser Sintering (SLS), and Fused Deposition Modeling (FDM). DIW, leveraging its advantages of broad material adaptability and support for multi-material printing, is suitable for the preparation of nanocomposites in laboratory settings; SLA/DLP offers high printing speed and precision but is only applicable to photosensitive resins, making it difficult to process composites containing opaque fillers; SLS achieves material shaping by laser sintering powder materials and is widely used in aerospace, biomedicine, and other fields; FDM features simple operation and low cost, and is commonly employed for printing thermoplastic polymers, whose material properties need to be enhanced through additive optimization.

(2) Mechanisms and Classification of Magnetically Responsive Materials
The core of magnetically responsive materials lies in achieving stable responses under the stimulation of static, alternating, or gradient magnetic fields, with their prominent characteristics including large-angle bending capability, ultra-fast response speed, high electromechanical conversion efficiency, and non-contact remote controllability. This review elaborates on four key types of materials in detail: Magnetic Shape Memory Alloys (MSMAs) possess high energy density and precise controllability, among which Ni-Mn-Ga alloys are a research hotspot, and their brittleness issue is addressed through composite modification or porous treatment; Magnetic Shape Memory Polymers (SMPs) and their composites consist of an SMP matrix and magnetic fillers such as Ni, Fe, and Fe₃O₄, combining high recoverable strain and processability; Magnetic Shape Memory Hydrogels realize shape memory through permanent crosslinking networks and reversible molecular switches, and can be extended to fields like environmental remediation and biomedicine after integrating magnetic particles; Magnetically Active Soft Materials (MASMs) are composed of magnetic particles compounded with flexible polymers, achieving programmable deformation via spatially encoded magnetization arrangements.

(3) Cross-disciplinary Applications of 4D Printing of Magnetically Responsive Materials
In biomedical tissue engineering, magnetically responsive 4D printing achieves precise deformation through non-contact magnetic field regulation, and is widely applied in intelligent scaffolds for tracheal repair, bone regeneration, tumor therapy, and other applications. In the field of robotics, biomimetic soft robots exhibit outstanding performance: snake-like robots possess multi-modal locomotion capabilities and high durability, while artificial cilia can realize high-viscosity liquid mixing; among medical microrobots, helical structures enable targeted delivery, and needle-like robots complete tumor localization and sustained drug release through an anchoring mechanism. In the direction of smart structures and devices, flexible sensors have achieved multi-physical quantity detection, electromagnetic architectures integrate millisecond-scale deformation and high-sensitivity sensing, single-material printing processes have promoted the efficient manufacturing of magnetoelectric dual-functional devices, and ultra-stretchable materials have further expanded the application potential of soft grippers and reconfigurable switches. Meanwhile, breakthroughs have also been made in fields such as acoustic regulation and mechanical metamaterials.

Future Outlook
Despite the significant progress achieved in magnetically responsive 4D printing technology, it still faces challenges such as limited magnetic strain of materials, insufficient printing precision for complex structures, and incomplete multi-field coupling theory. Future research should focus on developing new materials with higher magnetic strain and biocompatibility, while optimizing their printability; printing technology needs to advance toward multi-material synergy and micro-nano scale manufacturing, and integrate computational models to improve printing precision and efficiency. At the application level, efforts should be made to deepen its integration in interdisciplinary fields such as intelligent manufacturing and precision medicine. By constructing a "material-process-application" collaborative design framework and a "magnetic-electric-thermal" multi-field coupling response system, this technology will ultimately achieve a leap in deformation precision from the millimeter scale to the micrometer scale, bringing revolutionary changes to future intelligent systems.

The complete study is accessible via DOI:10.34133/research.0847