Hydrogels are promising materials for skin-interfaced bioelectronics due to their skin-like softness and high-water content. However, conventional hydrogels suffer from weak adhesion, rapid dehydration, deformation, and irreversible performance loss, especially on curved or mobile regions such as eyebrows, elbows, and fingers. These problems worsen in non-rehydratable systems that lose conformability and sensing stability after drying. To overcome them, we developed a bioadhesive-free, water-retentive, and rehydratable (BOWER) hydrogel based on thermoresponsive poly(N-isopropylacrylamide) (PNIPAAm) for long-term wearable sensing. While PNIPAAm provides soft skin adhesion near body temperature (~ 32 °C), its poor moisture stability was mitigated by integrating a composite electrospun nanofiber (NF) layer of hydrophilic polyvinyl alcohol (PVA) and polyethylene oxide (PEO) with hydrophobic waterborne polyurethane (WPU) on the top and sides, leaving the bottom uncoated for skin contact. This asymmetric design improved water retention from ~ 10 to > 14 h, suppressed dehydration under strain, and enabled full shape recovery and sensing restoration after rehydration. Incorporating conductive poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) imparted stable piezoresistive behavior with fast response and recovery (< 4 s) during joint motion, facial expression (ΔI/I₀ ~ 0.4), and respiration (~ 9 s). Maintaining a skin-like modulus (10–100 Pa) and scalability, the BOWER hydrogel offers a robust platform for multimodal, long-term wearable sensing.

As the first invention to efficiently harvest electricity from ambient mechanical energy by using contact electrification, the triboelectric nanogenerator has elicited worldwide attention because of its cost-effectiveness and sustainability. This study exploits a superhydrophobic nanostructured aluminum tube to estimate electrical output for solid-water contact electrification inside a tubular system. The linearly proportional relationship of short-circuit current and open-circuit voltage to the detaching speed of water was determined by using a theoretical energy harvesting model and experimentation. A pioneering stick-type solid-water interacting triboelectric nanogenerator, called a SWING stick, was developed to harvest mechanical energy through solid-water contact electrification generated when the device is shaken by hand. The electrical output generated by various kinds of water from the environment was also measured to demonstrate the concept of the SWING stick as a compact triboelectric nanogenerator. Several SWING sticks were connected to show the feasibility of the device as a portable and compact source of direct power. The developed energy harvesting model and the SWING stick can provide a guideline for the design parameters to attain a desired electrical output; therefore, this study can significantly increase the applicability of a water-driven triboelectric nanogenerator.