A Novel Porous PDMS-AgNWs-PDMS (PAP)-Sponge-Based Capacitive Pressure Sensor

High-Performance Triboelectric Nanogenerator Based on Silk Fibroin-MXene Composite Film for Diagnosing Insomnia Symptoms

In this study, we developed a flexible, biocompatible, and high-output electrical performance triboelectric nanogenerator (TENG) employing a silk fibroin (SF)-MXene composite film (SF-MXene-F) and a PDMS film as the friction layer. The inclusion of MXene in the SF film increased its surface charge density, presenting a practical approach to designing high-performance SF composite film-based TENGs. At a MXene content of 40%, our SF-MXene composite film-based TENG (SF-MXene-FTENG) achieved optimal output electrical performance, featuring a maximum open-circuit voltage (Voc) of 418 V, a maximum short-circuit current (Isc) of 11.6 μA, and a maximum output power density of 9.92 W/m2. The Voc and power densities of the SF-MXene-FTENG surpassed previously reported optimal values for SF-based TENGs by 1.6 and 3.8 times, respectively. Furthermore, leveraging the exceptional biocompatibility and light shading performance of TENGs, we designed a wearable smart TENG eye mask capable of diagnosing insomnia symptoms and monitoring sleep quality in real time. The SF-MXene-FTENG holds promising application potential as a wearable electronic device for diagnosing sleep-related diseases.

A Conductive and Anti-impact Composite for Flexible Piezoresistive Sensors

Flexible piezoresistive sensors, which can convert specific mechanical information (such as compression, bending, tensile, and torsion) into a resistance value change signal through the piezoresistive effect, have attracted more and more attention. However, how to achieve the simple, low-cost fabrication of a piezoresistive sensor is still a challenge. Herein, we report a facile strategy that introduces conductive carbon black (CB) and shear thickening gel (SG) composite into a melamine sponge (MS) to generate an MS-SG-CB composite with a unique force-electric coupling effect. A flexible sensor derived from the MS-SG-CB composite can not only accurately identify deformation signals during static stretching and compression while monitoring human movement status in real time but also recognize electrical signals under dynamic impact in a very short time (6 ms). The 3 × 3 flexible array built on this basis can accurately identify the mass and position of heavy objects. Furthermore, based on the flame-retardant properties of MS, the flame-retardant ammonium polyphosphate (APP) is further introduced into MS-SG-CB to obtain MS-SG-CB-APP composite with excellent flame retardancy and stable temperature electrical response behavior, expanding its application in the field of high temperature trigger alarm.

Highly Porous, Ultralight, Biocompatible Silk Fibroin Aerogel-Based Triboelectric Nanogenerator

This study presents the fabrication of an ultralight, porous, and high-performance triboelectric nanogenerator (TENG) utilizing silk fibroin (SF) aerogels and PDMS sponges as the friction layer. The transition from two-dimensional film friction layers to three-dimensional porous aerogels significantly increased the specific surface area, offering an effective strategy for designing high-performance SF aerogel-based TENGs. The TENG incorporating the porous SF aerogel exhibited optimal output performance at a 3% SF concentration, achieving a maximum open circuit voltage of 365 V, a maximum short-circuit current of 11.8 μA, and a maximum power density of 7.52 W/m2. In comparison to SF-film-based TENGs, the SF-aerogel based TENG demonstrated a remarkable 6.5-fold increase in voltage and a 4.5-fold increase in current. Furthermore, the power density of our SF-based TENG surpassed the previously reported optimal values for SF-based TENGs by 2.4 times. Leveraging the excellent mechanical stability and biocompatibility of TENGs, we developed an SF-based TENG self-powered sensor for the real-time monitoring of subtle biological movements. The SF-based TENG exhibits promising potential as a wearable bioelectronic device for health monitoring.

The Role of 3D Printing Technologies in Soft Grippers

Soft grippers are essential for precise and gentle handling of delicate, fragile, and easy-to-break objects, such as glassware, electronic components, food items, and biological samples, without causing any damage or deformation. This is especially important in industries such as healthcare, manufacturing, agriculture, food handling, and biomedical, where accuracy, safety, and preservation of the objects being handled are critical. This article reviews the use of 3D printing technologies in soft grippers, including those made of functional materials, nonfunctional materials, and those with sensors. 3D printing processes that can be used to fabricate each class of soft grippers are discussed. Available 3D printing technologies that are often used in soft grippers are primarily extrusion-based printing (fused deposition modeling and direct ink writing), jet-based printing (polymer jet), and immersion printing (stereolithography and digital light processing). The materials selected for fabricating soft grippers include thermoplastic polymers, UV-curable polymers, polymer gels, soft conductive composites, and hydrogels. It is conclude that 3D printing technologies revolutionize the way soft grippers are being fabricated, expanding their application domains and reducing the difficulties in customization, fabrication, and production.

Fabrication of a high performance flexible capacitive porous GO/PDMS pressure sensor based on droplet microfluidic technology

Porous structures are an effective way to improve the performance of flexible capacitive sensors, but the pore size uniformity of porous structures is not easily controlled by current methods, which may affect the inconsistent performance of different batches of sensors. In this paper, a high performance capacitive flexible porous GO/PDMS pressure sensor was prepared based on droplet microfluidic technology. By testing the performance of the sensor, we found that the sensor with a flow rate ratio of 1 : 3 has relatively good performance, with a degree of hysteresis (DH) of 8.64% and a coefficient of variation (CV) of 5.2%. Therefore, we studied the sensor performance based on this process. The result shows that the sensitivity of the flexible capacitive porous GO/PDMS pressure sensor reached 0.627 kPa-1 at low pressure (0-3 kPa), which is significantly higher than that of the pure PDMS thin film sensor (about 0.031 kPa-1) and the porous PDMS pressure sensor (0.263 kPa-1). At the same time, the sensor has a large range with a fast response time of 240 ms and a relaxation time of 300 ms at 30 kPa and an ultra-low detection limit (70 Pa). It can maintain stable operation under continuous force loading/unloading cycles and can respond well to different pressure step changes, so the sensor can be used to detect the movement process of each finger, knee, foot and other joints of the human body. In conclusion, the droplet microfluidic technology can effectively prepare high-performance capacitive flexible porous GO/PDMS pressure sensors.

Highly Electroconductive Metal-Polymer Hybrid Foams Based on Silver Nanowires: Manufacturing and Characterization

Due to their electroconductive properties, flexible open-cell polyurethane foam/silver nanowire (PUF/AgNW) structures can provide an alternative for the construction of cheap pressure transducers with limited lifetimes or used as filter media for air conditioning units, presenting bactericidal and antifungal properties. In this paper, highly electroconductive metal-polymer hybrid foams (MPHFs) based on AgNWs were manufactured and characterized. The electrical resistance of MPHFs with various degrees of AgNW coating was measured during repeated compression. For low degrees of AgNW coating, the decrease in electrical resistance during compression occurs in steps and is not reproducible with repeated compression cycles due to the reduced number of electroconductive zones involved in obtaining electrical conductivity. For high AgNW coating degrees, the decrease in resistance is quasi-linear and reproducible after the first compression cycle. However, after compression, cracks appear in the foam cell structure, which increases the electrical resistance and decreases the mechanical strength. It can be considered that PUFs coated with AgNWs have a compression memory effect and can be used as cheap solutions in industrial processes in which high precision is not required, such as exceeding a maximum admissible load or as ohmic seals for product security.

Rapid Prototyping Flexible Capacitive Pressure Sensors Based on Porous Electrodes

Flexible pressure sensors are widely applied in tactile perception, fingerprint recognition, medical monitoring, human-machine interfaces, and the Internet of Things. Among them, flexible capacitive pressure sensors have the advantages of low energy consumption, slight signal drift, and high response repeatability. However, current research on flexible capacitive pressure sensors focuses on optimizing the dielectric layer for improved sensitivity and pressure response range. Moreover, complicated and time-consuming fabrication methods are commonly applied to generate microstructure dielectric layers. Here, we propose a rapid and straightforward fabrication approach to prototyping flexible capacitive pressure sensors based on porous electrodes. Laser-induced graphene (LIG) is produced on both sides of the polyimide paper, resulting in paired compressible electrodes with 3D porous structures. When the elastic LIG electrodes are compressed, the effective electrode area, the relative distance between electrodes, and the dielectric property vary accordingly, thereby generating a sensitive pressure sensor in a relatively large working range (0-9.6 kPa). The sensitivity of the sensor is up to 7.71%/kPa^-1, and it can detect pressure as small as 10 Pa. The simple and robust structure allows the sensor to produce quick and repeatable responses. Our pressure sensor exhibits broad potential in practical applications in health monitoring, given its outstanding comprehensive performance combined with its simple and quick fabrication method.

Progress in Microtopography Optimization of Polymers-Based Pressure/Strain Sensors

Due to the wide application of wearable electronic devices in daily life, research into flexible electronics has become very attractive. Recently, various polymer-based sensors have emerged with great sensing performance and excellent extensibility. It is well known that different structural designs each confer their own unique, great impacts on the properties of materials. For polymer-based pressure/strain sensors, different structural designs determine different response-sensing mechanisms, thus showing their unique advantages and characteristics. This paper mainly focuses on polymer-based pressure-sensing materials applied in different microstructures and reviews their respective advantages. At the same time, polymer-based pressure sensors with different microstructures, including with respect to their working mechanisms, key parameters, and relevant operating ranges, are discussed in detail. According to the summary of its performance and mechanisms, different morphologies of microstructures can be designed for a sensor according to its performance characteristics and application scenario requirements, and the optimal structure can be adjusted by weighing and comparing sensor performances for the future. Finally, a conclusion and future perspectives are described.

Research Progresses in Microstructure Designs of Flexible Pressure Sensors

Flexible electronic technology is one of the research hotspots, and numerous wearable devices have been widely used in our daily life. As an important part of wearable devices, flexible sensors can effectively detect various stimuli related to specific environments or biological species, having a very bright development prospect. Therefore, there has been lots of studies devoted to developing high-performance flexible pressure sensors. In addition to developing a variety of materials with excellent performances, the microstructure designs of materials can also effectively improve the performances of sensors, which has brought new ideas to scientists and attracted their attention increasingly. This paper will summarize the flexible pressure sensors based on material microstructure designs in recent years. The paper will mainly discuss the processing methods and characteristics of various sensors with different microstructures, and compare the advantages, disadvantages, and application scenarios of them. At the same time, the main application fields of flexible pressure sensors based on microstructure designs will be listed, and their future development and challenges will be discussed.