A Softly Anchored Friction-fit Electrode (SAFE) for Highly Robust Mechanoelectrical Connections for Soft Sensors

Soft sensors using advanced materials like liquid metal and silver nanowires are now essential to wearable devices, providing both robust conductivity and high flexibility. However, forming a stable electrical connection with wires remains a significant challenge. The mechanical property mismatch compromises junction integrity, leading to frequent electrode failure and unstable signal acquisition. To overcome these limitations, this research proposes the ‘Softly Anchored Friction-fit Electrode (SAFE)’ for liquid metal-based soft sensors. The SAFE creates a liquid metal chamber with an inner diameter intentionally smaller than the outer diameter of the wire and utilizes a friction-fit anchoring. The wire is inserted into the chamber and doubly secured using silicone adhesive and an inextensible layer resistant to strain. Furthermore, this method simplifies the entire workflow into a straightforward 2D printing process. In pull-out tests on eight specimens of each type, the SAFE withstood average forces of 15.1 N before electrical failure and 17.9 N before mechanical failure, compared with 2.26 and 3.75 N for a direct ink writing-based electrode connection, corresponding to increases of 570 and 377%, respectively. The SAFE maintained a stable connection even after 200,000 cycles of repetitive deformation and under temperature variations (–20 to 50 °C). The SAFE significantly enhances electromechanical reliability while preserving the inherent advantages of soft sensors, thereby increasing the practical reliability of real-world wearable devices.