Flexible pressure sensors (FPSs) have been widely studied in the fields of wearable medical monitoring and human-machine interaction due to their high flexibility, light weight, sensitivity, and easy integration. To better meet these application requirements, key sensing properties such as sensitivity, linear sensing range, pressure detection limits, response/recovery time, and durability need to be effectively improved. Therefore, researchers have extensively and profoundly researched and innovated on the structure of sensors, and various microstructures have been designed and applied to effectively improve the sensing performance of sensors. Compared with single microstructures, multiple microstructures (MMSs) (including hierarchical, multi-layered and hybrid microstructures) can improve the sensing performance of sensors to a greater extent. This paper reviews the recent research progress in the design and application of FPSs with MMSs and systematically summarizes the types, sensing mechanisms, and preparation methods of MMSs. In addition, we summarize the applications of FPSs with MMSs in the fields of human motion detection, health monitoring, and human-computer interaction. Finally, we provide an outlook on the prospects and challenges for the development of FPSs.

Recent progress in flexible pressure sensors based on multiple microstructures: from design to application.

Piezoelectric polymer materials have been extensively investigated as key materials for small kinetic energy harvesting due to their advantages over inorganic piezoelectric materials, such as high flexibility, good processability, and the possibility of a large area as well as curved surface preparation. However, the difficulty of working at high temperatures is a huge challenge for polymeric piezoelectric materials. Therefore, researchers have not stopped their quest to develop new piezoelectric polymer materials with higher performance. This paper first describes the design mechanism of piezoelectric polyacrylonitrile (PAN), analysing its structure and fabrication techniques, as well as its advantages, problems, and structural design challenges. Subsequently, methods to improve the high-temperature piezoelectric properties of PAN by changing the molecular structure and blending with inorganic materials/high-temperature resistant polymers are presented. Research on the application of PAN piezoelectric polymers in nanogenerators, acoustoelectric conversion, sensors, and high temperature thermoacoustic conversion are summarized. Finally, the status, problems, and potential of PAN high-temperature piezoelectric polymers are revealed, and the future directions of various PAN properties in different fields are foreseen. 

A Review: Polyacrylonitrile as high-performance piezoelectric materials

Recent progress in electrospun polyvinylidene fluoride (PVDF)-based nanofibers for sustainable energy and environmental applications

Polyacrylonitrile (PAN) nanofiber-based flexible piezoelectric sensors are recognized for their applicability in wearable electronic devices, personal health monitoring, and motion detection. This research explores the impact of dual fillers, MXene and polydopamine-modified zinc oxide (PDA@ZnO), on the characteristics of PAN-based piezoelectric composite nanofiber films, including planar zigzag conformation content, dielectric, ferroelectric, piezoelectric, and mechanical properties. By integrating PDA@ZnO as a filler, PAN/MXene/PDA@ZnO-5 (PMPO) piezoelectric sensors were developed, showcasing enhanced piezoelectric sensing capabilities. These sensors achieved a sensitivity of 28.56 V/N across a broad linear range, with superior mechanical stability and durability across 3000 loading–unloading cycles, and exhibited swift response and recovery times of 49 ms and 40 ms, respectively. Furthermore, their unique fiber structure and flexibility, when interfaced with the human body, enable the detection of minute physiological movements and the conversion of varied motions into distinct voltage outputs. Thus, these sensors offer considerable promise for applications in human health monitoring and motion posture correction. 

Flexible piezoelectric sensor based on PAN/MXene/PDA@ZnO composite film for human health and motion detection with fast response and highly sensitive

Poly(vinylidene fluoride) (PVDF) is a renowned piezoelectric polymer, but its widespread application is hindered by its low β phase content. This research presents the fabrication of PVDF/SiC, PVDF/FeCl3, and PVDF/SiC/FeCl3 composite nanofiber membranes via an electrospinning technique. Among these, the PVDF/SiC/FeCl3 composite nanofiber-based piezoelectric nanogenerator (PENG) exhibited the best output performance. This enhancement is primarily due to the synergistic effect of incorporating SiC and FeCl3 into the PVDF matrix, which significantly increases the β phase content of PVDF, thereby enhancing the piezoelectric properties of the PENG. The flexible PENG arrays composed of PVDF/SiC/FeCl3 composite membranes hold great promise for use in smart socks for gait monitoring, particularly for early corrective measures in preschool children. This innovation is expected to have a significant impact on the fields of sports, medical monitoring, and other related areas. 

Flexible PVDF/SiC/FeCl3 nanofiber membrane generators with synergistically enhanced piezoelectricity

ABSTRACT Mechanical ventilation can induce lung injury and exacerbate brain injury due to lung-brain interaction. The current study sought to investigate the mechanism of lung-brain interaction induced by mechanical ventilation and offer theoretical insight into the management of ventilator-induced brain injury. The experimental mice were assigned into the spontaneously breathing group and the mechanical ventilation group and injected with dopamine (DA) receptor antagonist haloperidol or P2Y1 receptor antagonist MRS2279 before ventilation. In vitro assay was conducted using lung epithelial cells MLE-12 hippocampal neuron cells and HT-22. Mouse recognition function and lung injury were examined. The condition and concentration of neurons in the hippocampus were observed. The levels of several inflammatory factors, DA, adenosine triphosphate (ATP), P2Y1R, and dysbindin-1 were detected. Mechanical ventilation induced lung and brain injury in mice, manifested in increased inflammatory factors in the bronchoalveolar lavage fluid and hippocampus, prolonged escape latency, and swimming distance and time in the target quadrant with a weakened concentration of neurons in the hippocampus. Our results presented elevated ATP and P2Y1R expressions in the mechanically ventilated mice and stretched MLE-12 cells. The mechanically ventilated mice and P2Y1 receptor activator MRS2365-treated HT-22 cells presented with elevated levels of DA and dysbindin-1. Inactivation of P2Y1 receptor in the hippocampus or blockage of DA receptor alleviated brain injury induced by mechanical ventilation in mice. To conclude, the current study elicited that lung injury induced by mechanical ventilation exacerbated brain injury in mice by increasing ATP production, activating the P2Y1 receptor, and thus promoting DA release.

https://www.tandfonline.com/doi/pdf/10.1080/21655979.2021.2022269?needAccess=true

Mechanical ventilation induces lung and brain injury through ATP production, P2Y1 receptor activation and dopamine release

Enhanced piezoelectric performance of rare earth complex-doped sandwich-structured electrospun P(VDF-HFP) multifunctional composite nanofiber membranes

Here, we demonstrate the design and application of a multifunctional piezoelectric composite nanofiber membrane. In this study, the most widely used electrospinning method, by adding a small amount of 1-allyl-3-butylimidazolium tetrafluoroborate ionic liquids and ferric chloride hexahydrate (FeCl3·6H2O) to regulate the structure and properties of polyacrylonitrile (PAN), the mechanical properties, piezoelectric properties, dielectric properties, and ferroelectric properties of composite nanofibers were improved. The results show that the piezoelectric properties of PAN composite fibers are greatly improved under the action of dual fillers. At 103 Hz, the dielectric constant of the PAN composite fiber is as high as 8.24, which is three times that of the pure PAN fiber. The sensor made from the composite nanofibers exhibits excellent sensitivity and high saturation polarization. At low pressure (<1 kPa), the sensitivity of the composite fiber is as high as 0.51 kPa. When we tap the sensor with our finger, the PAN composite fiber produces high piezoelectric output (5.7 V). The results show that the composite nanofibers have great potential in energy storage devices and flexible piezoelectric sensors, among other fields. 

Enhanced the dielectric and piezoelectric properties of polyacrylonitrile piezoelectric composite fibers filled with ionic liquids

Lightweight, flexible, and hydrophobic multifunctional piezoelectric sensors have increasingly important research value in contemporary society. They can generate electrical signals under the action of pressure and can be applied in various complex scenarios. In this study, we prepared a polyacrylonitrile (PAN) composite fiber doped with imidazolium type ionic liquids (ILs) and europium nitrate hexahydrate (Eu (NO3)3·6H2O) by a facile method. The results show that the PAN composite fibers had excellent mechanical properties (the elongation at break was 114% and the elastic modulus was 2.98 MPa), hydrophobic self-cleaning ability (water contact angle reached 127.99°), and can also emit light under UV light irradiation red fluorescence. In addition, thanks to the induction of the piezoelectric phase of PAN by the dual fillers, the composite fibers exhibited efficient energy storage capacity and excellent sensitivity. The energy density of PAN@Eu-6ILs reached a maximum of 44.02 mJ/cm3 and had an energy storage efficiency of 80%. More importantly, under low pressure detection, the sensitivity of the composite fiber was 0.69 kPa−1. The research results show that this PAN composite fiber has the potential to act as wearable piezoelectric devices, energy storage devices, and other electronic devices.

/pdf/a-flexible-multifunctional-pan-piezoelectric-fiber-with-3pxopciw.pdf

A Flexible Multifunctional PAN Piezoelectric Fiber with Hydrophobicity, Energy Storage, and Fluorescence

In this paper, barium titanate nanoparticles (BaTiO3, BT) were incorporated into the polyurethane (TPU) matrix to prepare dielectric elastomer composites. Then, the composites were thermal treated to improve the interfacial compatibility between TPU and BT, enhance the interface polarization, and improve the dielectric properties. The results showed that the dielectric constant of the composites after thermal treatment at 150°C reached to 7.3 at 1 kHz, the elongation at break remained 1934%, and the elastic modulus (Y) dropped to 4.4 MPa. In addition, the discharge energy density reached 73 mJ/cm3 under an electric field of 300 kV/cm, and charge–discharge energy conversion efficiency was up to 84%. More importantly, the electrically actuated displacement of 2.61 mm at electric field of 160 kV/cm was 1.7 times greater than that of untreated composites. The composites worked stably under the action of the circulating electric field. This study provided a new strategy for obtaining high-performance dielectric elastomer actuators, which were expected to be applied to biomimetic robots, human skin, or dielectric energy storage devices. 

Enhanced dielectric, energy storage, and actuated performance of
 TPU
 /
 
 BaTiO
 3
 
 dielectric elastomer composites by thermal treatment

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Papers

Mechanical ventilation induces lung and brain injury through ATP production, P2Y1 receptor activation and dopamine release

Enhanced piezoelectric performance of rare earth complex-doped sandwich-structured electrospun P(VDF-HFP) multifunctional composite nanofiber membranes

Enhanced the dielectric and piezoelectric properties of polyacrylonitrile piezoelectric composite fibers filled with ionic liquids

A Flexible Multifunctional PAN Piezoelectric Fiber with Hydrophobicity, Energy Storage, and Fluorescence

Enhanced dielectric, energy storage, and actuated performance of TPU / BaTiO 3 dielectric elastomer composites by thermal treatment