Core–Sheath Stretchable Conductive Fibers for Safe Underwater Wearable Electronics

Abstract Stretchable conductive fibers can be directly woven into textiles and applied in wearable and implantable electronic devices. However, for a stretchable conductive fiber that is capable of safely using in full water environment with strains when contacting to skin, it is challenging. Herein, an ultrafine core–sheath stretchable conductive fiber (CSCF in short) with insulative outer sheath and conductive inner core is designed particularly for safe underwater electronic skin devices. CSCF starts from prestrained Lycra fiber followed by spray coating 1D conductive species (carbon nanotubes (CNTs)/silver nanowires (AgNWs)) and wrapping styrene‐(ethylene‐butylene)‐styrene (SEBS) thin film. CSCF exhibits stable core conductivity (e.g., R₀ ≈ 2 × 10⁴ S m⁻¹, ΔR/R₀ ≈ 0.1 at 100% strain) as well as surface insulation upon mechanical stretching in full water environment. The thickness‐tunable SEBS not only protects skin away from leak of CNTs and AgNWs, but also efficiently suppresses leakage current to an extremely safe level (<1 µA at 5 V) when applying in underwater electronic skin devices. A wireless charging patch composed by CSCF induction coil is able to light light emitting diode (LEDs) no matter when CSCFs are folding and stretching in water. These advantages highlight the promising application of stretchable conductive fiber with protective polymer skin for safe underwater wearable electronics.