3D MXene-Based Flexible Network for High-Performance Pressure Sensor with a Wide Temperature Range

Architectural design and affecting factors of MXene-based textronics for real-world application

Today, textile-based wearable electronic devices (textronics) have been developed by taking advantage of nanotechnology and textile substrates. Textile substrates offer flexibility, air permeability, breathability, and wearability, whereas, using nanomaterials offers numerous functional properties, like electrical conductivity, hydrophobicity, touch sensitivity, self-healing properties, joule heating properties, and many more. For these reasons, textronics have been extensively used in many applications. Recently, new emerging two-dimensional (2D) transition metal carbide and nitride, known as MXene, nanomaterials have been highly considered for developing textronics because the surface functional groups and hydrophilicity of MXene nanoflakes allow the facile fabrication of MXene-based textronics. In addition, MXene nanosheets possess excellent electroconductivity and mechanical properties as well as large surface area, which also give numerous opportunities to develop novel functional MXene/textile-based wearable electronic devices. Therefore, this review summarizes the recent advancements in the architectural design of MXene-based textronics, like fiber, yarn, and fabric. Regarding the fabrication of MXene/textile composites, numerous factors affect the functional properties (e.g. fabric structure, MXene size, etc.). All the crucial affecting parameters, which should be chosen carefully during the fabrication process, are critically discussed here. Next, the recent applications of MXene-based textronics in supercapacitors, thermotherapy, and sensors are elaborately delineated. Finally, the existing challenges and future scopes associated with the development of MXene-based textronics are presented.

Ultrawide linear range, high sensitivity, and large-area pressure sensor arrays enabled by pneumatic spraying broccoli-like microstructures

Large-area pressure sensor arrays with a wide linear response range and high sensitivity are beneficial to map the inhomogeneous interface pressure, which is significant in practical applications. Here, we demonstrate a pneumatic spraying method to prepare large-area microstructure films (PSMF) for high performance pressure sensor arrays. The sprayed surface morphology is designable by controlling the spraying parameters. It is worth noting that the constructed "broccoli" like morphology with a swollen top and shrunken bottom inspired a new mechanism to enlarge the linear response range by decreasing the series resistance with pressure increasing. At the same time, the pneumatic sprayed "broccoli" has a rough surface due to droplet stacking, which reduces the initial current effectively. Hence, the sensor achieves a 10 000 kPa ultrawide linear response range with a high sensitivity (98.71 kPa-1), and low detection (5 Pa). The prepared sensor has a small static response error (4.4%) and 5000 cycle full-range dynamic response durability. Finally, the constructed sensor arrays can distinguish the pressure distribution in different ranges clearly, which indicates a great potential in health care, motion detection, and the tire industry.

Skin-Inspired Textile Electronics Enable Ultrasensitive Pressure Sensing

Wearable pressure sensors have attracted great interest due to their potential applications in healthcare monitoring and human-machine interaction. However, it is still a critical challenge to simultaneously achieve high sensitivity, low detection limit, fast response, and outstanding breathability for wearable electronics due to the difficulty in constructing microstructure on a porous substrate. Inspired by the spinosum microstructure of human skin for highly-sensitive tactile perception, a biomimetic flexible pressure sensor is designed and fabricated by assembling MXene-based sensing electrode and MXene-based interdigitated electrode. The product biomimetic sensor exhibits good flexibility and suitable air permeability (165.6 mm s-1), comparable to the typical air permeable garments. Benefiting from the two-stage amplification effect of the bionic intermittent structure, the product bionic sensor exhibits an ultrahigh sensitivity (1368.9 kPa-1), ultrafast response (20 ms), low detection limit (1 Pa), and high-linearity response (R2 = 0.997) across the entire sensing range. Moreover, the pressure sensor can detect a wide range of human motion in real-time through intimate skin contact, providing essential data for biomedical monitoring and personal medical diagnosis. This principle lays a foundation for the development of human skin-like high-sensitivity, fast-response tactile sensors.

Flexible and Simply Degradable MXene-Methylcellulose Piezoresistive Sensor for Human Motion Detection

Flexible pressure sensors are intensively demanded in various fields such as electronic skin, medical and health detection, wearable electronics, etc. MXene is considered an excellent sensing material due to its benign metal conductivity and adjustable interlayer distance. Exhibiting both high sensitivity and long-term stability is currently an urgent pursuit in MXene-based flexible pressure sensors. In this work, high-strength methylcellulose was introduced into the MXene film to increase the interlayer distance of 2D nanosheets and fundamentally overcome the self-stacking problem. Thus, concurrent improvement of the sensing capability and mechanical strength was obtained. By appropriately modulating the ratio of methylcellulose and MXene, the obtained pressure sensor presents a high sensitivity of 19.41 kPa-1 (0.88-24.09 kPa), good stability (10000 cycles), and complete biodegradation in H2O2 solution within 2 days. Besides, the sensor is capable of detecting a wide range of human activities (pulse, gesture, joint movement, etc.) and can precisely recognize spatial pressure distribution, which serves as a good candidate for next-generation wearable electronic devices.

MXene-Based Chemo-Sensors and Other Sensing Devices

MXenes have received worldwide attention across various scientific and technological fields since the first report of the synthesis of Ti3C2 nanostructures in 2011. The unique characteristics of MXenes, such as superior mechanical strength and flexibility, liquid-phase processability, tunable surface functionality, high electrical conductivity, and the ability to customize their properties, have led to the widespread development and exploration of their applications in energy storage, electronics, biomedicine, catalysis, and environmental technologies. The significant growth in publications related to MXenes over the past decade highlights the extensive research interest in this material. One area that has a great potential for improvement through the integration of MXenes is sensor design. Strain sensors, temperature sensors, pressure sensors, biosensors (both optical and electrochemical), gas sensors, and environmental pollution sensors targeted at volatile organic compounds (VOCs) could all gain numerous improvements from the inclusion of MXenes. This report delves into the current research landscape, exploring the advancements in MXene-based chemo-sensor technologies and examining potential future applications across diverse sensor types.

Constructed MXene matrix composites as sensing material and applications thereof: A review

Most studies on MXene matrix composites for sensor development have primarily focused on synthesis and application. Nevertheless, there is currently a lack of research on how the introduction of different materials affects the sensing properties of these composites. The rapid development of MXene has raised intriguing questions about improving sensor performance by combining MXene with other materials such as polymers, metals and inorganic non-metals. This review will concentrate on the construction of MXene-based composites and explore ways to enhance their sensor applications. Specifically, this review describes why the introduction of materials to the system brings the advantage of low concentration and high sensitivity assays, as well as the MXene-based frameworks that have been recently investigated. Lastly, in order to capture the current trend of MXene-based composites in sensor applications and identify promising research directions, this review will critically evaluate the potential applications of newly developed MXene systems.

Wearable Safeguarding Leather Composite with Excellent Sensing, Thermal Management, and Electromagnetic Interference Shielding

This work illustrates a "soft-toughness" coupling design method to integrate the shear stiffening gel (SSG), natural leather, and nonwoven fabrics (NWF) for preparing leather/MXene/SSG/NWF (LMSN) composite with high anti-impact protecting, piezoresistive sensing, electromagnetic interference (EMI) shielding, and human thermal management performance. Owing to the porous fiber structure of the leather, the MXene nanosheets can penetrate leather to construct a stable 3D conductive network; thus both the LM and LMSN composites exhibit superior conductivity, high Joule heating temperature, and an efficient EMI shielding effectiveness. Due to the excellent energy absorption of the SSG, the LMSN composites possess a huge force-buffering (about 65.5%), superior energy dissipation (above 50%), and a high limit penetration velocity of 91 m s-1 , showing extraordinary anti-impact performance. Interestingly, LMSN composites possess an unconventional opposite sensing behavior to piezoresistive sensing (resistance reduction) and impact stimulation (resistance growing), thus they can distinguish the low and high energy stimulus. Ultimately, a soft protective vest with thermal management and impact monitoring performance is further fabricated, and it shows a typical wireless impact-sensing performance. This method is expected to have broad application potential in the next-generation wearable electronic devices for human safeguarding.

Pressure Sensor Based on a Lumpily Pyramidal Vertical Graphene Film with a Broad Sensing Range and High Sensitivity

Wearable sensors are vital for the development of electronic skins to improve health monitoring, robotic tactile sensing, and artificial intelligence. Active materials and the construction of microstructures in the sensitive layer are the dominating approaches to improve the performance of pressure sensors. However, it is still a challenge to simultaneously achieve a sensor with a high sensitivity and a wide detection range. In this work, using three-dimensional (3D) vertical graphene (VG) as an active material, in combination with micropyramid arrays and lumpy holders, the stress concentration effects are generated in nano-, micro-, and macroscales. Therefore, the lumpily pyramidal VG film-based pressure sensor (LPV sensor) achieves an ultrahigh sensitivity (131.36 kPa^-1) and a wide response range (0.1-100 kPa). Finite element analysis demonstrates that the stress concentration effects are enhanced by the micropyramid arrays and lumpy structures in micro- and macroscales, respectively. Finally, the LPV pressure sensors are tested in practical applications, including wearable health monitoring and force feedback of robotic tactile sensing.