Electrolyte-jet 3D printing of copper-based strain sensors for physiological signal monitoring and robotic manipulation

Novel strategies for strain sensor fabrication are continually emerging, driving advancements in performance and design. Thermal 3D printing has enabled the innovation of high-performance sensors with diverse geometries and applications. However, the direct production of conductive fillers and the direct regulation of filler distribution via current 3D processes remain challenges. Electrochemical 3D printing offers a promising alternative, facilitating the fabrication of metal fillers under ambient conditions. Using a custom-built electrolyte jet (EJ) 3D printer, low-cost Cu microspheres are synthesized from industrial wastewater with adjustable size and density. These Cu microspheres, integrated with spray-coated carbon nanofibers (CNFs), self-assemble into an “island-bridge” hybrid network interlayered within polydimethylsiloxane (PDMS) layers. This configuration establishes a distinctive piezoresistive mechanism, imparting the sensor with high sensitivity (GF = 133.2), a broad working range (ɛ: 0–70%), and remarkable durability (up to 6490 cycles of repeatability). When applied in human joints, the sensor allows real-time detection of human motions and precise control of robotic systems. It demonstrates reliable functionality under extreme temperatures and in natural seawater, showcasing outstanding environmental adaptability. Incorporating electrochemical 3D printing technology into conventional sensor fabrication processes paves the way for the highly controllable and sustainable production of advanced multi-environmental strain sensors.