textiles that are washable with lifetimes similar to conventional textiles. [9][10][11][12][13] Furthermore, our daily life cannot be without water, such as raining, bathing, swimming, and etc. With underwater wearable electronics, underwater activities can be effectively detected or analyzed, for example monitoring electrophysiological signals for athletes when they are training in the rain or water, detecting the moving, migration or feeling of the living creatures underwater. Therefore, to design stretchable conductive fibers capable of working in full water environment is fundamentally essential. Typical methods of developing stretchable conductive fibers include prestraining polymer fibers to induce the attached 1D conductive species (metal nanowires or carbon nanotubes (CNTs)) into wavy structure, [3,14] wrapping conductive species into spiral shape along an elastic polymer fiber, [3,10,[15][16][17][18][19] or using a conductive liquid or gel encapsulated in an elastomer. [20][21][22] However, liquid metal conductors are susceptible to leakage if the fibers are damaged, while hydrogel conductors dry out over time, and both exhibit changes in conductance of the fibers with strain. Carbon-based conductors have low conductivity with increasing length, [7,9,14,17,23,24] while metal composite conductors typically exhibit limited strain tolerance and poor cycle stability. [25,26] Conductive fibers with waterproof [27] or splash-resistance [28] have been studied, but stretchable conductive fibers that are capable of maintaining good conductivity at high strain as well as fully underwater long-time use have not been systematically reported yet.In this work, we presented a core-sheath stretchable conductive fiber (CSCF) which could be safely used in water and other harsh environments (such as sonication) for a long time. The ultrafine CSCF (≈30 µm in diameter) is composed of Lycra (polyurethane, PU) fiber, multiwall carbon nanotubes (MWCNTs), silver nanowires (AgNWs), and styrene-(ethylenebutylene)-styrene (SEBS) sequentially from inside to outside, which is defined as PU@CNTs@AgNWs@SEBS. Spray coating 1D conductive networks onto a prestraining Lycra fiber resulted in a highly stretchable conductive fiber (e.g., ΔR/R 0 ≈ 0.1 at 100% strain, cycled >100 000 times at 50% strain). Surface coating SEBS enabled a significantly reduced leakage both in current (<1 µA at 5 V) and element (Ag), thus safe to human

Stretchable conductors have been achieved by stacking conductive nanomaterials onto the surfaces of elastomeric substrates. However, many of them show a dramatic decrease in conductivity under strain without an efficient way for the conductive layer to release strain. Here, we report a transparent, stretchable, and self-healing conductor with excellent mechanoelectrical stability by introducing dynamic bonding between conductive nanomaterials and an elastomeric substrate. We prepare the conductor by semiembedding Ag nanowires (AgNWs) into a self-healing polydimethylsiloxane (PDMS)-based elastomer, which is modified with bipyridine (Bpy) ligand and further cross-linked by adding Zn2+ as coordinator (Zn–Bpy–PDMS). The dynamic Ag–N bonds not only improve the wettability of the substrate and facilitate the spreading of AgNWs but also reversibly break and reform to accommodate the deformation of AgNWs. As a result, the resistance increase of Zn–Bpy–PDMS/AgNWs is much smaller than that without the dynamic bonding (PDMS/AgNWs). Besides, this conductor exhibits excellent conductivity (76.2 Ω/sq) and transparency (86.6% @ 550 nm), as well as extraordinary self-healing property with a low resistance increase (ΔR/R 0 ∼ 1.4) after healing at room temperature for 1 day. This work provides insights into the future design of integrated electronic skin with transparency, stretchability, conductivity, and self-healing capability for applications in wearable optoelectronic devices.

Epidermal biopotential monitoring is an essential part of wearable healthcare. For 24 × 7 h detection of electrophysiological signals, commercialized gel electrodes cannot satisfy the demands, in particular for monitoring in humidity or underwater. Epidermal electrodes that can be stable and operated underwater are required. Here, a highly conductive and optically camouflaged ionic skin for epidermal biopotential monitoring under aquatic circumstances is designed. There is a fluorine‐dipole interaction system consisting of fluorine‐rich segment in the polyurethane backbone and fluorine‐cation bonded 1‐ethyl‐3‐methylimidazolium bis(trifluoromethyl‐sulfonyl) imide ([EMIM]+ [TFSI]−) ion pairs distributed in the polymer matrix. Benefitting from the fluorine‐cation interaction, the ionic skin gains remarkable ionic conductivity (1.04 × 10−3 S cm−1), high optical transmittance (92%), and improved mechanical strength (3.1 MPa of Young's modulus). Via cations caught by fluorine‐rich segments, its ionic conductivity can keep stable even by rinsing or fierce washing in water. The epidermal electrode based on such ionic skin can accurately measure a variety of electrophysiological signals undboth atmospheric and aquatic environments, exhibiting robust and excellent signal quality. As the first demonstration of ionic skin‐based electrophysiological electrodes, the ionic skin paves a new way for all‐day wearable healthcare.