Cold Extrusion of Stretchable Liquid Metal–Polymer Composite Feedstock for Intrinsically Conductive 3D Printing

Abstract

Additive manufacturing of soft conductive materials enables flexible electronics, sensors, and robotic systems, yet is often constrained by high-temperature melt processing, postprint activation, or rigid conductive inclusions that reduce compliance. Here, we introduce a cold-extrusion strategy to create feedstock for liquid metal (LM)/thermoplastic elastomer composites that overcomes these limitations, enabling additive manufacturing of intrinsically conductive soft structures. By lightly solvating the polymer matrix, the composite enters a transient, putty-like processing state that enables extrusion without elevated temperature while preserving high LM loading (>60 vol %) and uniform droplet dispersion. Crucially, we leverage the high shear forces inherent to the extrusion process to drive droplet coalescence within the putty, directly forming a feedstock with a percolated, electrically conductive network. The continuously extruded LM/thermoplastic polyurethane feedstock is then pelletized and directly fabricated into multidimensional, conductive architectures using elevated-temperature extrusion-based 3D printing, without the need for thermal sintering, mechanical embossing, or secondary conductive inclusions. The printed composites reach notable conductivities of 0.4–1.8 × 104 S/m while retaining extensibility above 200% strain, demonstrating an additive manufacturing workflow that enables simultaneous printability, conductivity, and mechanical compliance. These results establish a general strategy for additive manufacturing of conductive thermoplastic elastomer composites for scalable fabrication of soft electronic and robotic systems.