Multi-material printing of 3D heterogeneous structures with embedded microscale conductive features for electromagnetic function

Multi-material printing has recently gained extensive attention as an efficient strategy for the integrated fabrication of 3D heterogeneous structures with microscale conformal/embedded electronics in the field of antennas or metasurface. However, as one of the most popularly utilized multi-material printing processes, fused filament fabrication (FFF) commonly suffers from poor surface morphology, which poses a significant challenge for the subsequent deposition of conductive features with micro-resolution and stable conductivity. Here, we propose a novel multi-material printing strategy by combining coaxial electrohydrodynamic (CEHD) printing and FFF for the one-step fabrication of 3D heterogeneous structures with conformal or embedded microelectronics. It is found that the outer polyimide (PI) layer applied during the CEHD process can locally smooth the FFF-printed PEEK surfaces with varying roughness and enables the direct deposition of microscale core-shell conductive features with stable conductivity. Remarkably, the smallest conductive linewidth of Ag that can be achieved on an FFF-printed surface with a roughness of 23.57 ± 6.24 μm is 42.10 ± 3.45 μm, showing a conductivity of (0.32 ± 0.01) × 10⁷ S/m. The proposed strategy demonstrates wide applicability across different substrate materials and geometries, and exhibits strong interfacial bonding strength and excellent electrical stability under different mechanical/physical conditions. More importantly, the presented multi-material printing technique offers great flexibility in integrally fabricating 3D heterogeneous structures with built-in microelectronics. The patterns of the embedded microelectronics exhibit a layer-specific variation, which demonstrates an innovative strategy to modulate the electromagnetic functionalities of the resultant heterogeneous structures. We envision that the proposed multi-material printing technique offers a unique capability to integrally fabricate mechanical/electrical structures with designed electromagnetic functionalities, enabling applications in curved conformal antennas and electromagnetic shielding devices.