Grayscale 4D Printing of Ferromagnetic Soft Materials.

Ferromagnetic 4D printing offers rapid shape deformations via external magnetic fields, enabling innovations in soft robotics, adaptive structures, and biomedical devices. However, achieving both high load-bearing capacity and large deformation requires a balance of mechanical properties, traditionally addressed by integrating rigid and soft components in multi-material systems. Such approaches increase complexity, slow down manufacturing with vat exchanges and cleaning, and limit design flexibility. Here, a ferromagnetic grayscale 4D printing strategy is introduced that combines digital light processing (DLP) grayscale 3D printing with ferromagnetic particles within a single-material system. By precisely controlling light intensity during printing, this method allows localized mechanical property programming and, fabrication structures with coexisting soft and rigid domains. This approach is validated by fabricating grayscale cantilever beams and analyzing their bending and response under magnetic fields. The technique achieves high load-bearing capacity (supporting up to 42.6 times its weight), suitable bending angles (98.6% improvement at 200 mT), and rapid responsiveness (87% increase at 2 s). These capabilities are demonstrated through the crawling robot and "M", "U" structures, showcasing practical potential. This study offers a streamlined approach to ferromagnetic 4D printing, reducing the need for complex multi-material processes while expanding the scope of advanced material applications.