Indirectly Activated 4D Printing of Thermoplastic Polyurethane Graphene Nanoplatelet Composites

This work presents the design and in-depth characterization of thermoplastic polyurethane (TPU) composites enhanced with graphene nanoplatelets (GNPs) for 4D printing using Fused Filament Fabrication (FFF). TPU-GNP nanocomposites containing 2-8 wt.% filler were compounded, extruded into printable filaments, and 3D printed into functional specimens. Multiscale investigations, encompassing thermal, mechanical, electrical, and morphological analyses, revealed that GNP inclusion significantly altered the mechanical properties (E +144%, σ max -59%, ε max -96%) improved thermal conductivity (up to 1.02 W/mK) and enabled electrical conductivity (2.92 × 10 -4 S cm⁻ 1 ) sufficient for triggering shape recovery via the Joule effect. Shape memory capabilities were assessed through fold-deploy experiments, demonstrating excellent shape fixity and recovery ratios (> 90%) and fast actuation times below 10 seconds. A functional hinge prototype, fabricated with the optimal composite formulation, was successfully activated through remote Joule-heating (45 V and power of ∼6 W) achieving complete deployment within 120 s, showcasing its applicability in deployable structures.