Multi-material 3D printing-enabled multilayers for smart actuation via magnetic and thermal stimuli

Transitional compositions or phase-changing structures in specific layers can respond to environmental changes differently and show intelligent behaviors. For example, smart polymers with shape morphing capabilities (e.g., external field-controlled untethered actuation) have found applications in angle-changing solar panel support, crawling soft microrobots, targeted drug delivery, tissue scaffolds, and directional heat dissipation in microelectronics. However, conventional processing has constraints in layer stacking, thus limiting the manufacturing efficiency, structural flexibility, and material compatibility. Therefore, this research will leverage an in-house 3D printing platform for rapidly prototyped, multi-material, and multiphase layers. Furthermore, our multiphase direct ink writing (MDIW) 3D printing allows for a one-step assembly of different polymers and nanoparticles in composite multilayers within each printed line (e.g., a microscale resolution). To demonstrate the smart actuation via thermal and magnetic fields, we selected ester- and ether-based thermoplastic polyurethane (TPU) polymers, polycaprolactone (PCL), and iron oxide (Fe₃O₄) nanoparticles that are selectively mixed and combined as printing feedstocks. The particular position of different polymers and particles led to layers with distinct anisotropy, enabling varying actuation efficiency when these composites were fixed at different orientations with respect to the printing texture. As a result of the unique 3D printing platform and composite microstructures, this research provides an efficient protocol for fabricating multiphase composite layers with smart behaviors for broad applications.