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A novel flexible zinc oxide/poly­(vinylidene fluoride) (ZnO/PVDF) nanocomposite was prepared by electrospinning for fabricating a piezoelectric nanogenerator (PNG). The ZnO nanoparticles (NPs) and nanorods (NRs) were used as nanofillers of piezoelectric PVDF to prepare fibrous nanocomposite membranes. It has been found that the addition of piezoelectric ZnO NPs and NRs can improve the overall performance of the PNGs fabricated with the electrospun membranes. A large electrical throughput (open circuit voltage ∼85 V and short circuit current ∼2.2 μA) from the ZnO NR/PVDF fiber membrane-based PNG (ZR-PNG) indicates that ZnO NRs are effective functional fillers for PVDF. The high aspect ratio and flexibility characteristics of ZnO NRs were found to be highly beneficial for improving the piezoelectric properties of the nanocomposites. ZnO NRs act as nucleating agents of β-phase PVDF, and ZnO NRs can also produce piezoelectric charges when they deform with the composite fibrous membrane. It has been concluded that the obvious synergistic effects between the piezoelectric nanofillers and electroactive β-crystals of PVDF in the ZnO NRs/PVDF composites are useful for the construction of the high-performance flexible PNG. In addition, the fabricated ZR-PNG can light up commercial light emitting diodes (40 white, 36 blue) and charge the capacitors in a very short time (3 V is accomplished in 25 s), which indicates the potential of the ZR-PNG for portable, wearable, flexible, or self-powered electronic devices.

Tough, biocompatible, and conductive hydrogel-based strain sensors are attractive in the fields of human motion detection and wearable electronics, whereas it is still a great challenge to simultaneously integrate underwater adhesion and self-healing properties into one hydrogel sensor. Here, a highly stretchable, sensitive, and multifunctional polysaccharide-based dual-network hydrogel sensor was constructed using dialdehyde carboxymethyl cellulose (DCMC), chitosan (CS), poly(acrylic acid) (PAA), and aluminum ions (Al 3+ ). The obtained DCMC/CS/PAA (DCP) composite hydrogels exhibit robust mechanical strength and good adhesive and self-healing properties, due to the reversible dynamic chemical bonds and physical interactions such as Schiff base bonds and metal coordination. The conductivity of hydrogel is 2.6 S/m, and the sensitivity (gauge factor (GF)) is up to 15.56. Notably, the DCP hydrogel shows excellent underwater repeatable adhesion to animal tissues and good self-healing properties in water (self-healing rate > 90%, self-healing time < 10 min). The DCP hydrogel strain sensor can sensitively monitor human motion including finger bending, smiling, and wrist pulse, and it can steadily detect human movement underwater. This work is expected to provide a new strategy for the design of high-performance intelligent sensors, particularly for applications in wet and underwater environments.

Flexible wearable sensors are expected to be the future generation of personal health monitoring devices with large‐area, multimodal, multipoint sensing, and complicated data analysis. However, multimaterial interfacial coalescence and mechanical matching critically challenge the advancement of flexible devices and multifunction integration. Graphene, with characteristic carbon sheet 2D material, is endowed with good transparency, stability, superior electron mobility, heat conductivity, excellent flexibility, and mechanical performance. A summary of the progresses of flexible graphene‐based sensors in terms of material processing, sensor configuration, and property is presented. Various assembly structures could perform different electrical behaviors with unitary graphene material. The diversity of graphene‐based temperature, humidity, pressure, strain, and integrated multifunctional sensors developed in recent years is detailed. Benefitting from the commendable flexible mechanical performance and high durability, flexible graphene‐based sensors promote practical applications in body temperature monitoring, voice recognition, pulse‐beating, motion, and respiration detection. Finally, future research following the development trends and challenges of integrated graphene‐based sensors to develop their potential in human health monitoring and human–machine interfaces are discussed.

Four model polyurethane (PU) hard segments were synthesized by reaction of butanol with four typical diisocyanates. The four diisocyanates were aromatic 4,4′-diphenylmethane diisocyanate (4,4′-MDI) and MDI-50 (50% mixture of 2,4′-MDI and 4,4′-MDI), cycloaliphatic 4,4′-dicyclohexylmethane diisocyanate (HMDI) and linear aliphatic 1,6-hexamethylene diisocyanate (HDI). FTIR, 1H NMR, 13C NMR, MS, X-ray and DSC methods were employed to determine their structures and to analyse their crystallization behaviours and hydrogen bonding interactions. Each of the four PU compounds prepared in the present work displays unique spectral characteristics. The FTIR bands and NMR resonance peaks assigned in the four samples thus provide a reliable database and starting point for investigating the relationship between hard segment structure and the crystallization and hydrogen bonding behaviour in more complex-segmented PU compositions.

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Hydrogel-based flexible wearable devices have attracted wide attention from researchers due to their great potential application in human–computer interaction, electronic skin, and disease diagnosis. However, the preparation of conductive hydrogels integrating good biocompatibility, excellent mechanical (tensile and compressible) properties, self-adhesive properties, cyclic stretching, and compression stability remains a challenge. By the Schiff base reaction between dialdehyde carboxymethyl cellulose and amino gelatin to form the first layer of the network and by the free-radical polymerization of acrylic acid to form the second layer of the network, a multifunctional conductive dual-network (DN) hydrogel strain sensor was prepared. The composite DN hydrogel has excellent compression properties (the strength reached to 0.12 MPa when the hydrogel was compressed to 50% of its original height), good cyclic compression (≥10 000 times), repeatable adhesion (≥10 times), reliable electrical conductivity, and high sensitivity (gauge factor = 8.1). The biocompatible hydrogel can be used not only to monitor human body movement but also to detect the breathing movement of simulated pig lungs in vitro. Furthermore, the conductive hydrogel was creatively made into a plantar pressure sensor similar to an insole to monitor the stress on the sole of a flatfoot patient, providing a new potential material for flatfoot detection and correction.