Multiphase Direct Ink Writing (MDIW) of Layered Structures for Stimuli-Responsive Behaviors*

Intelligent devices are extensively studied due to their versatile functionality and plethora of applications like targeted drug delivery for cancer cell treatment or deep ocean reach in soft robotics. Stimuli-responsive polymers, including smart materials or shape memory polymers (SMP), have attracted much attention in additive manufacturing due to their ability to produce complex structures in all shapes. This work demonstrated the one-step fabrication of composite multiphase smart materials using the newly developed multiphase direct ink writing (MDIW) 3D printing process. The SMPs were formulated using ether and ester-based thermoplastic polyurethane (TPU) mixed with polycaprolactone (PCL) and iron oxide nanoparticles (Fe₂O₃), respectively, providing the temperature and magnetic responsive properties. The MDIW mechanism produces alternative layers of the materials giving an isotropic responsive behavior of the as-fabricated structures to the external stimuli. The fabricated shape-memory structures also had a wide range of thermal actuation temperature (40 - 65°C), high strain, and shape recovery rate (up to 500%).