Hydrogel‐based strain sensors have attracted considerable interest for applications such as skin‐like electronics for human motion detection, soft robotics, and human–machine interfaces. However, fabrication of hydrogel strain sensors with desirable mechanical and piezoresistive properties is still challenging. Herein, a biocompatible hydrogel sensor is presented, which is made of polyvinyl alcohol (PVA) nanocomposite with high stretchability up to 500% strain, high mechanical strength of 900 kPa, and electrical conductivity (1.85 S m‐1) comparable to human skin. The hydrogel sensors demonstrate excellent linearity in the whole detection range and great durability under cyclic loading with low hysteresis of 7%. These excellent properties are believed to be contributed by a new bilayer structural design, i.e., a thin, conductive hybrid layer of PVA/silver nanowires (AgNWs) deposited on a pure strong PVA substrate. PVA solution of high concentration is used to fabricate the substrate while the top layer consists of dilute PVA solution so that high content of AgNWs can be dispersed to achieve high electrical conductivity. Together with a rapid response time (0.32 s) and biocompatibility, this new sensor offers great potential as a wearable sensor for epidermal sensing applications, e.g., detecting human joint and muscle movements.

This paper suggests development of a flexible, lightweight, and ultra-sensitive piezoresistive flow sensor based on vertical graphene nanosheets (VGNs) with a mazelike structure. The sensor was thoroughly characterized for steady-state and oscillatory water flow monitoring applications. The results demonstrated a high sensitivity (103.91 mV (mm/s)−1) and a very low-velocity detection threshold (1.127 mm s−1) in steady-state flow monitoring. As one of many potential applications, we demonstrated that the proposed VGNs/PDMS flow sensor can closely mimic the vestibular hair cell sensors housed inside the semicircular canals (SCCs). As a proof of concept, magnetic resonance imaging of the human inner ear was conducted to measure the dimensions of the SCCs and to develop a 3D printed lateral semicircular canal (LSCC). The sensor was embedded into the artificial LSCC and tested for various physiological movements. The obtained results indicate that the flow sensor is able to distinguish minute changes in the rotational axis physical geometry, frequency, and amplitude. The success of this study paves the way for extending this technology not only to vestibular organ prosthesis but also to other applications such as blood/urine flow monitoring, intravenous therapy (IV), water leakage monitoring, and unmanned underwater robots through incorporation of the appropriate packaging of devices.

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unmanned underwater robots, [3] sleep apnea treatment, [4] and other biomedical applications. [5] Among these, mimicking sensory hair cells that are ubiquitous in the creatures such as fish lateral line, crocodile body, locust's legs, mammalian vestibular system, and hearing system has attracted significant interest among many researchers. In nature, sensory hair cells work based on mechanical deflection induced by flow, vibration, acoustic vibration, and gravitational force, generating electrochemical signals and transmitting them to the brain. [6,7] The organs of balance (saccule, utricle, and semicircular canals) are filled with a fluid called the endolymph, which has a high concentration of potassium (K + ) ions and is low in sodium (Na + ) ions. When a linear or angular acceleration occurs, the ciliary tip links stretch or relax, depending on movement direction. In the case of the links stretching, the tip-links' channels are opened, allowing entry of particular cations (including potassium) into the cell, causing depolarization in the cell.

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