Electrically conductive filament for 3D-printed circuits and sensors

• 3D printable polypropylene-based conductive filament (<0.01 Ω m) has been achieved. • Electrical and UV stress tests demonstrated stability of printed conductors. • Practical plastic thermometer and flex sensor were 3D printed. 3D printing is a unique technology that potentially offers a high degree of freedom for the customization of practical products that incorporate electrical components, such as sensors in wearable applications. The availability of inexpensive, reliable, electrically conductive material will be indispensable in the fabrication of such circuits and sensors before the full potential of 3D printing for customized products incorporating electrical elements can be realized. To date, 3D printable conductive filaments with sufficiently high conductivities to fabricate practical circuits remain lacking for fused deposition modeling. Herein, we describe the fabrication, characterization, stress testing, and application of a low-cost thermoplastic conductive composite that has been processed into filament form for 3D printing. Results from stress tests show that the electrical properties of our composites are stable under exposure to sunlight over 1 month and there was no observable degradation in electrical resistance when used at 12 V (AC) for 7 days. Practical circuits were 3D printed using filaments with resistivity of ∼5 × 10 −3 Ω m, and powered up with a 9 V battery. A plastic thermometer and a flex sensor were prototyped to illustrate the potential of this material for sensing applications, for example, in customized wearables.