In the present study, we propose and develop a flexible pressure sensor based on the piezoresistive effect of multilayer graphene films on polyester textile. The pressure response results from the deformation of graphene conductive network structure and the changes in resistance. Here, we show that the graphene pressure sensor can achieve a sensitivity value of 0.012 kPa ${}^{-1}$ , the measurement range can be as high as 800 kPa, and the response time can reach to 50 ms. Subsequently, a stable in-shoe wireless plantar pressure measurement system is developed and dynamic pressure distribution is acquired in real-time. Overall, the graphene textile pressure sensor has the advantage of wide dynamic range, flexibility and comfort, which provides the high possibility for footwear evaluation, clinical gait analysis and pathological foot diagnosis.

This paper describes the development of a graphene-based dry flexible electrocardiography (ECG) electrode and a portable wireless ECG measurement system. First, graphene films on polyethylene terephthalate (PET) substrates and graphene paper were used to construct the ECG electrode. Then, a graphene textile was synthesized for the fabrication of a wearable ECG monitoring system. The structure and the electrical properties of the graphene electrodes were evaluated using Raman spectroscopy, scanning electron microscopy (SEM), and alternating current impedance spectroscopy. ECG signals were then collected from healthy subjects using the developed graphene electrode and portable measurement system. The results show that the graphene electrode was able to acquire the typical characteristics and features of human ECG signals with a high signal-to-noise (SNR) ratio in different states of motion. A week-long continuous wearability test showed no degradation in the ECG signal quality over time. The graphene-based flexible electrode demonstrates comfortability, good biocompatibility, and high electrophysiological detection sensitivity. The graphene electrode also combines the potential for use in long-term wearable dynamic cardiac activity monitoring systems with convenience and comfort for use in home health care of elderly and high-risk adults.

An important challenge in the study of functional corticomuscular coupling (FCMC) is an accurate capture of the coupling relationship between the cerebral cortex and the effector muscle. The coherence method is a linear analysis method, which has certain limitations in further revealing the nonlinear coupling between neural signals. Although mutual information (MI) and transfer entropy (TE) based on information theory can capture both linear and nonlinear correlations, the equitability of these algorithms is ignored and the nonlinear components of the correlation cannot be separated. The maximal information coefficient (MIC) is a suitable method to measure the coupling between neurophysiological signals. This study extends the MIC to the time–frequency domain, named time–frequency maximal information coefficient (TFMIC), to explore the FCMC in a specific frequency band. The effectiveness, equitability, and robustness of the algorithm on the simulation data was verified and compared with coherence, TE- and MI- based methods. Simulation results showed that the TFMIC could accurately detect the coupling for different functional relationships at low noise levels. The dorsiflexion experimental results revealed that the beta-band (14–30 Hz) significant coupling was observed at channels Cz, C4, FC4, and FCz. Additionally, the results showed that the coupling was higher in the alpha-band (8– 13 Hz) and beta-band (14–30 Hz) than in the gamma-band (31–45 Hz). This might be related to a transition between sensorimotor states. Specifically, the nonlinear component of FCMC was also observed at channels Cz, C4, FC4, and FCz. This study expanded the research on nonlinear coupling components in FCMC.

The center of plantar pressure (COP) reflects the dynamic balance of subjects to a certain extent. In this study, wearable pressure insoles are designed, body pose measure is detected by the Kinect sensor, and a balance evaluation system is formulated. With the designed games for the interactive actions, the Kinect sensor reads the skeletal poses to judge whether the desired action is performed, and the pressure insoles simultaneously collect the plantar pressure data. The COP displacement and its speed are calculated to determine the body sway and the ability of balance control. Significant differences in the dispersion of the COP distribution of the 12 subjects have been obtained, indicating different balancing abilities of the examined subjects. A novel assessment process is also proposed in the paper, in which a correlation analysis is made between the de facto sit-to-stand (STS) test and the proposed method; the Pearson and Spearman correlations are also conducted, which reveal a significant positive correlation. Finally, four undergraduate volunteers with a right leg sports injury participate in the experiments. The experimental results show that the normal side and abnormal side have significantly different characters, suggesting that our method is effective and robust for balance measurements.

A novel, highly sensitive gas sensing system that uses a graphene-coated quartz tuning fork (QTF), based on light-induced thermoelastic spectroscopy (LITES) is developed. Graphene films with different thicknesses are deposited on commercially available QTF to improve the light absorption and thermoelastic effect. The optimum coating thickness is obtained experimentally and used for gas detection. CO ₂ is selected as the target analyte for performance verification, and a gain factor of 1.8 and 1.7 is attained for the sensitivity and SNR, respectively, when compared to traditional LITES using bare QTF. A minimum detection limit of 0.06% was obtained corresponding to a normalized noise equivalent absorption coefficient of 5.78×10 ^-10 cm ^-1 ·\textW·Hz ^-1/2 , and a measurement precision of approximately 0.1 ppm was achieved with an integration time of 300 s. The method of spin coating film on a commercially available QTF exhibits the advantages of low-cost, simplicity, and ease of operation; moreover, the strong UV to THz light absorption of graphene offers a promising strategy for sensitive trace gas analysis and ultra-broad band optical detection.

Ionogels have garnered great attention for fabricating flexible soft ionotronics as they can mimic human skin that responds to external stimuli. However, the low detection sensitivity and limited responsiveness as well as the complicated fabrication process significantly limit their wide applications. Herein, a skin-inspired stretchable, compressible, self-adhesive ionogel with gradient and hierarchical microstructures and properties has been prepared by a one-step electric-field assisted photo-polymerization method. By regulating the ions of ionic liquids (ILs) and poly(ionic liquid)s (PILs), these PIL ionogels also exhibit good adjustable hydrophilicity/hydrophobicity and environmental adaptability. Based on the gradient conductivity capacity along with the gradient mechanical structure, the gradient ionogel-based flexible ionotronic shows high sensitivity up to 1.0 kPa⁻¹ over a wide range of detection up to 400 kPa, low minimum detection (0.15 Pa), fast response time (8 ms), wide working temperature range (−85 to 360 °C), and good durability (5000 cycles). More importantly, the developed high-resolution pressure-sensing array can accurately detect the contour and output three-dimensional pressure distribution maps. Furthermore, advanced soft ionotronic sensors with multimodal sensation capabilities are further designed, which can detect various motions, such as liquid drop sensing, human joint motion detection, and real-time pulse wave monitoring.