Highly sensitive and flexible strain sensor based on AuNPs/CNTs’ synergic conductive network

Highly Sensitive and Wide Detection Range Thermoplastic Polyurethane/Graphene Nanoplatelets Multifunctional Strain Sensor with a Porous and Crimped Network Structure

High-performance flexible strain sensors have tremendous potential applications in wearable devices and health monitoring. However, developing a flexible strain sensor with high sensitivity over a wide strain range remains a significant challenge. In this study, a fibrous membrane with a porous and crimped structure was designed as the substrate material for TPU/GNPs flexible strain sensors. This structural design effectively balances sensitivity with the strain range. The TPU-PEO fibrous membrane prepared using electrospinning with water washing, resulted in a porous fibrous membrane with a TPU framework. Subsequently, the fibrous membrane was subjected to anhydrous ethanol stimulation to obtain a porous and crimped network structure. GNPs were modified on the TPU fibrous membrane through ultrasonic treatment. The produced flexible strain sensor exhibited high sensitivity (GF = 4047.5) within a large strain range (350%) and demonstrated excellent sensing performance, stability, and durability (>10,000 cycles). It not only captured basic movements but also efficiently recognized and measured bending angles, enabling a more sophisticated human-machine interaction experience. This advancement opens up possibilities for future intelligent wearable technology and human-machine interaction, contributing to the evolution of these fields.

Research status of polysiloxane-based piezoresistive flexible human electronic sensors

Flexible human body electronic sensor is a multifunctional electronic device with flexibility, extensibility, and responsiveness. Piezoresistive flexible human body electronic sensor has attracted the extensive attention of researchers because of its simple preparation process, high detection sensitivity, wide detection range, and low power consumption. However, the wearability and affinity to the human body of traditional flexible human electronic sensors are poor, while polysiloxane materials can be mixed with other electronic materials and have good affinity toward the human body. Therefore, polysiloxane materials have become the first choice of flexible matrixes. In this study, the research progress and preparation methods of piezoresistive flexible human electronic sensors based on polysiloxane materials in recent years are summarized, the challenges faced in the development of piezoresistive flexible human electronic sensors are analyzed, and the future research directions are prospected.

Low-hysteresis, pressure-insensitive, and transparent capacitive strain sensor for human activity monitoring

Wearable strain sensors have been widely used for human activity monitoring. Most reported strain sensors have mainly focused on material engineering, high stretchability and large gauge factors. Few works have focused on strain sensor's robustness and reliability, including low hysteresis, good long-term stability, good electrode material stability, and low coupling effects under multi-input signals, which are the factors that limit practical strain sensor applications. To develop a high-performance strain sensor, we propose a flexible capacitive sensor structure with three-dimensional (3D) interdigital electrodes fabricated by vertically aligned carbon nanotubes. Compared with a traditional resistive strain sensor and a capacitive strain sensor with vertical sandwich electrodes, a strain sensor with horizontal parallel interdigital electrodes can benefit from low cross talk in terms of the normal force and improve substrate transparency. Additionally, embedding 3D electrodes into the substrate improves ultrahigh robustness with a low-pressure coupling effect under normal force. Moreover, compared with other reported works, the electrode variation under strain is small (less than 1.6%), which means that the perturbation of inert properties on device performance is small. Finally, the fabricated strain sensor achieves an ultralow hysteresis (0.35%), excellent pressure-insensitive performance (less than 0.8%), fast response (60 ms), good long-term stability, and good transparency. As an application example, a flexible strain sensor was successfully demonstrated as a wearable device for the precise monitoring of different types of human activities, including bending of the finger, knee, elbow, wrist, and neck with large strain signals and small strain signals generated by a mouth-opening activity. This excellent performance indicates that the flexible strain sensor is a promising candidate for human motion detection, soft robotics, and medical care.

Sensing mechanism of a flexible strain sensor developed directly using electrospun composite nanofiber yarn with ternary carbon nanomaterials

Recently, various strain-sensing yarns have been developed without ideal stitchability. Herein, we used spherical carbon black particles (CBs), linear carbon nanotubes (CNTs), and lamellar graphene flakes (GRs) as conductive nanofillers to construct multi-element conductive networks inside a thermoplastic polyurethane (TPU) matrix. First, a highly stretchable and conductive multidimensional carbon-based nanomaterial/TPU composite nanofiber yarn was fabricated using electrospinning, which could be used as a flexible strain sensor without post-processing. Accordingly, the effects of nanomaterials’ dimensionality and synergy on yarns’ conductivity, mechanical properties, and strain sensing performances were explored. The yarn containing multiple networks formed by CB/CNT/GR ternary hybrid networks, CNT and GR auxiliary networks exhibited the best performances. Subsequently, the structural evolution of the ternary conductive network under stretching was revealed to further analyze the sensing mechanism. Finally, the yarn endowed a medicated plaster with an intelligent function to detect motions in the rehabilitation of joint pain by simple sewing.

•

An anti-interference and washable strain-sensing composite nanofiber yarn

•

Synergy of carbon black particles, carbon nanotubes, and graphene flakes

•

Strain-sensing mechanism of ternary conductive networks are revealed

•

A smart medicated plaster can detect motions in the rehabilitation of joint pain

Inherently Conductive Poly(dimethylsiloxane) Elastomers Synergistically Mediated by Nanocellulose/Carbon Nanotube Nanohybrids toward Highly Sensitive, Stretchable, and Durable Strain Sensors

With the rapid development of soft electronics, flexible and stretchable strain sensors are highly desirable. However, coupling of high sensitivity and stretchability in a single strain sensor remains a challenge. Herein, a kind of conductive elastomer is constructed with poly(dimethylsiloxane) (PDMS) and silylated cellulose nanocrystal (SCNC)/carbon nanotube (CNT) nanohybrids through a facile one-pot solution-casting method. The hydrophobic SCNCs can effectively facilitate the dispersion of CNTs in PDMS and synergistically improve the interfacial compatibility between CNTs and the PDMS matrix, resulting in favorable stress and electron transfer in the polymer network. Due to the outstanding electrical conductivity of CNTs and the excellent dispersity and high mechanical performance of SCNCs, combined with the good compatibility between SCNC-mediated carbon nanotubes (SCNC-CNTs) and PDMS, the resulting composite elastomer (SCNC-CNT/PDMS) shows high electrical conductivity (∼2.77 S m^-1), tensile strength (∼5.72 MPa), and fatigue resistance properties. The strain sensor assembled by SCNC-CNT/PDMS demonstrates a high strain range above 100%, appealing strain sensitivity with a gauge factor of 37.11 at 50-100% strain, and long-term stability and durability, which is capable of monitoring both real-time human motions and acoustic vibrations. This work paves a new way for the design and controllable preparation of flexible and stretchable conductive elastomers, demonstrating promising applications in wearable devices and intelligent electronics.

Surface stress-induced membrane biosensor based on double-layer stable gold nanostructures for E. coli detection

The surface stress-based biosensor has been applied in fast and sensitive identification of Escherichia coli (E. coli)with significance for public health, food, and water safety. However, the stable sensitive element of flexible biosensor based on surface stress is still crucial and challengeable. Here, the authors reported surface stress-induced biosensors based on double-layer stable gold nanostructures (D-AuNS-SSMB) for E. coli O157:H7 detection. Bacterial detection demonstrates the high stability of the biosensor. The resistance change of biosensor is linear to the logarithmic value of the E. coli O157:H7 concentrations ranging from 10³ to 10⁷ CFU/mL with a limit of detection (LOD) of 43 CFU/mL. The captured signals of D-AuNS-SSMB comes from surface stress generated by antigen-antibody binding. In addition, the biosensor exhibits good stability, reproducibility and specificity in detection of E. coli O157:H7 as well. This study provides a new preparation method of stable sensitive element for the E. coli detection.

Sensitivity-Tunable Strain Sensors Based on Carbon Nanotube@Carbon Nanocoil Hybrid Networks

A novel vanelike nanostructure based on the hybridization of carbon nanotubes and carbon nanocoils has been fabricated by a two-step chemical vapor deposition method. A flexible and sensitive strain sensor is prepared by coupling this hybrid structure with polydimethylsiloxane. By regulating the density and length of carbon nanotubes, the gauge factor and strain range of the sensors are tuned from 4.5 to 70 and 9 to 260%, respectively. These sensors exhibit high reliability and stability in a more than 10 000-cycle test and have a prompt response time of less than 37 ms. Owing to the tunable properties, these sensors show great potential in monitoring both subtle and large-scale displacements, which can meet the diverse demands of human motion monitoring.