Printing Stretchable Electronics With Fused Filament Fabrication

Additive manufacturing is a powerful approach for integrating flexible and stretchable conductors into complex 3-D structures, but many current printing technologies, such as direct ink writing (DIW), are expensive and challenging to access for many potential users, such as hobbyists and small companies. In this work, a low-cost commercial fused filament fabrication (FFF) 3-D printer is used to manufacture low-resistivity stretchable serpentine conductors. By using dual extruder heads, serpentines are printed in a highly conductive metal-particulate-based composite on a thermoplastic elastomer (TPE) part and demonstrated to survive mechanical strains of up to 25%, sufficient for use in close contact with the human body. Selective electroless plating is also demonstrated to metalize the printed traces, depositing a thin layer of copper for improved electrical conductivity. Using this approach, we demonstrate conductivity improvements by about three orders of magnitude ( $\sim10^{3}$ ) over past FFF printed serpentines, a major milestone in making stretchable electronics cheaper and more accessible. The resulting stretchable conductors are then demonstrated to print devices, including stretchable inductors and stretchable interconnect on a soft robotic actuator.