Highly Sensitive E-Textile Strain Sensors Enhanced by Geometrical Treatment for Human Monitoring

Strain Sensors Made of MXene, CNTs, and TPU/PSF Asymmetric Structure Films with Large Tensile Recovery and Applied in Human Health Monitoring

Designing flexible wearable sensors with a wide sensing range, high sensitivity, and high stability is a vulnerable research direction with a futuristic field to study. In this paper, Ti3C2Tx MXene/carbon nanotube (CNT)/thermoplastic polyurethane (TPU)/polysulfone (PSF) composite films with excellent sensor performance were obtained by self-assembly of conductive fillers in TPU/PSF porous films with an asymmetric structure through vacuum filtration, and the porous films were prepared by the phase inversion method. The composite films consist of the upper part with finger-like "cavities" filled by MXene/CNTs, which reduces the microcracks in the conductive network during the tensile process, and the lower part has smaller apertures of a relatively dense resin cortex assisting the recovery process. The exclusive layer structure of the MXene/CNTs/TPU/PSF film sensor, with a thickness of 46.95 μm, contains 0.0339 mg/cm2 single-walled carbon nanotubes (SWNTs) and 0.348 mg/cm2 MXene only, providing functional range (0-80.7%), high sensitivity (up to 1265.18), and excellent stability and durability (stable sensing under 2300 fatigue tests, viable to the initial resistance), endurably cycled under large strains with serious damage to the conductive network. Finally, the MXene/CNTs/TPU/PSF film sensor is usable for monitoring pulse, swallow, tiptoe, and various joint bends in real time and distributing effective electrical signals. This paper implies that the MXene/CNTs/TPU/PSF film sensor has broad prospects in pragmatic applications.

Highly Inductive Coil Spring Strain/Compress Sensors Integrated with Shape Memory Alloy and Shape Memory Polymers-CNTs

Future wearable electronic gadgets offer great potential for using stretchable, strain-sensitive materials to instantly detect human motion and record physiological information. This paper presens a strain/compress sensor made from a Shape memory alloy (SMA) coil spring covered with silver pastes and the composite of carbon nanotubes and Shape memory polymer (SMP). The combination of the shape memory materials that expand or contract automatically by temperature improved the mechanics of the sensor. First, the proposed sensors showed an excellent ability to broad-range strain of 250% and compress of 50% with a relative inductance (∆L/L0 ) range from -35% to 50%, respectively. Durability during 1000 loading and unloading cycles at 200% strain is included. Secondly, by monitoring changes in resistance, inductance, and time, it is determined how many silver layers appropriate for transformation should be in order to improve the recovery time of the SMA coil spring. Moreover, the presence of CNTs in the composite-covered outer of sensors helps to reduce the influence of the relation between resistance and temperature in the range from 30 °C to 110 °C. Finally, a device is suggested for monitoring arm and triceps brachii muscle movements based on the stretchable area as a key parameter.

Novel SMD Component and Module Interconnection and Encapsulation Technique for Textile Substrates Using 3D Printed Polymer Materials

Nowadays, a range of sensors and actuators can be realized directly in the structure of textile substrates using metal-plated yarns, metal-filament yarns, or functionalized yarns with nanomaterials, such as nanowires, nanoparticles, or carbon materials. However, the evaluation or control circuits still depend upon the use of semiconductor components or integrated circuits, which cannot be currently implemented directly into the textiles or substituted by functionalized yarns. This study is focused on a novel thermo-compression interconnection technique intended for the realization of the electrical interconnection of SMD components or modules with textile substrates and their encapsulation in one single production step using commonly widespread cost-effective devices, such as 3D printers and heat-press machines, intended for textile applications. The realized specimens are characterized by low resistance (median 21 mΩ), linear voltage-current characteristics, and fluid-resistant encapsulation. The contact area is comprehensively analyzed and compared with the theoretical Holm's model.

Design and Fabrication of Embroidered Textile Strain Sensors: An Alternative to Stitch-Based Strain Sensors

Smart textile sensors have been gaining popularity as alternative methods for the continuous monitoring of human motion. Multiple methods of fabrication for these textile sensors have been proposed, but the simpler ones include stitching or embroidering the conductive thread onto an elastic fabric to create a strain sensor. Although multiple studies have demonstrated the efficacy of textile sensors using the stitching technique, there is almost little to no information regarding the fabrication of textile strain sensors using the embroidery method. In this paper, a design guide for the fabrication of an embroidered resistive textile strain sensor is presented. All of the required design steps are explained, as well as the different embroidery design parameters and their optimal values. Finally, three embroidered textile strain sensors were created using these design steps. These sensors are based on the principle of superposition and were fabricated using a stainless-steel conductive thread embroidered onto a polyester-rubber elastic knit structure. The three sensors demonstrated an average gauge factor of 1.88±0.51 over a 26% working range, low hysteresis (8.54±2.66%), and good repeatability after being pre-stretched over a certain number of stretching cycles.

Functionalized Fiber-Based Strain Sensors: Pathway to Next-Generation Wearable Electronics

Wearable strain sensors are arousing increasing research interests in recent years on account of their potentials in motion detection, personal and public healthcare, future entertainment, man-machine interaction, artificial intelligence, and so forth. Much research has focused on fiber-based sensors due to the appealing performance of fibers, including processing flexibility, wearing comfortability, outstanding lifetime and serviceability, low-cost and large-scale capacity. Herein, we review the latest advances in functionalization and device fabrication of fiber materials toward applications in fiber-based wearable strain sensors. We describe the approaches for preparing conductive fibers such as spinning, surface modification, and structural transformation. We also introduce the fabrication and sensing mechanisms of state-of-the-art sensors and analyze their merits and demerits. The applications toward motion detection, healthcare, man-machine interaction, future entertainment, and multifunctional sensing are summarized with typical examples. We finally critically analyze tough challenges and future remarks of fiber-based strain sensors, aiming to implement them in real applications.

Ultrafast-Response/Recovery Flexible Piezoresistive Sensors with DNA-Like Double Helix Yarns for Epidermal Pulse Monitoring

A key challenge in textile sensors is to adequately solve the hysteresis for more broad and exacting applications. Unlike the conventional strategy in integrating elastic polymers into the textile, the hysteretic issue is critically addressed here through the structural design of yarns to provide a twisting force. The underlying mechanism is fully discussed based on theory and modeling, which are in good agreement with experimental data. Impressively, the pressure sensor outperforms almost all reported textile-based sensors in terms of recovery index, which refers to the ability to overcome the lagged deformation reflected by the hysteresis (5.3%) and relaxation time (2 ms). Besides, the sensor superiority is also demonstrated by way of its ultrafast response time (2 ms). Thanks to these merits, this pressure sensor is demonstrated to be capable of monitoring epidermal pulses and meanwhile shows great potential to advance the standardization and modernization of pulse palpation in traditional Chinese medicine.

The E-Textile for Biomedical Applications: A Systematic Review of Literature

The use of e-textile technologies spread out in the scientific research with several applications in both medical and nonmedical world. In particular, wearable technologies and miniature electronics devices were implemented and tested for medical research purposes. In this paper, a systematic review regarding the use of e-textile for clinical applications was conducted: the Scopus and Pubmed databases were investigate by considering research studies from 2010 to 2020. Overall, 262 papers were found, and 71 of them were included in the systematic review. Of the included studies, 63.4% focused on information and communication technology studies, while the other 36.6% focused on industrial bioengineering applications. Overall, 56.3% of the research was published as an article, while the remainder were conference papers. Papers included in the review were grouped by main aim into cardiological, muscular, physical medicine and orthopaedic, respiratory, and miscellaneous applications. The systematic review showed that there are several types of applications regarding e-textile in medicine and several devices were implemented as well; nevertheless, there is still a lack of validation studies on larger cohorts of subjects since the majority of the research only focuses on developing and testing the new device without considering a further extended validation.

Effects of 3D Printing-Line Directions for Stretchable Sensor Performances

Health monitoring sensors that are attached to clothing are a new trend of the times, especially stretchable sensors for human motion measurements or biological markers. However, price, durability, and performance always are major problems to be addressed and three-dimensional (3D) printing combined with conductive flexible materials (thermoplastic polyurethane) can be an optimal solution. Herein, we evaluate the effects of 3D printing-line directions (45°, 90°, 180°) on the sensor performances. Using fused filament fabrication (FDM) technology, the sensors are created with different print styles for specific purposes. We also discuss some main issues of the stretch sensors from Carbon Nanotube/Thermoplastic Polyurethane (CNT/TPU) and FDM. Our sensor achieves outstanding stability (10,000 cycles) and reliability, which are verified through repeated measurements. Its capability is demonstrated in a real application when detecting finger motion by a sensor-integrated into gloves. This paper is expected to bring contribution to the development of flexible conductive materials-based on 3D printing.

Ultrasensitive Strain Sensor Based on Pre-Generated Crack Networks Using Ag Nanoparticles/Single-Walled Carbon Nanotube (SWCNT) Hybrid Fillers and a Polyester Woven Elastic Band

Flexible strain sensors are receiving a great deal of interest owing to their prospective applications in monitoring various human activities. Among various efforts to enhance the sensitivity of strain sensors, pre-crack generation has been well explored for elastic polymers but rarely on textile substrates. Herein, a highly sensitive textile-based strain sensor was fabricated via a dip-coat-stretch approach: a polyester woven elastic band was dipped into ink containing single-walled carbon nanotubes coated with silver paste and pre-stretched to generate prebuilt cracks on the surface. Our sensor demonstrated outstanding sensitivity (a gauge factor of up to 3550 within a strain range of 1.5-5%), high stability and durability, and low hysteresis. The high performance of this sensor is attributable to the excellent elasticity and woven structure of the fabric substrate, effectively generating and propagating the prebuilt cracks. The strain sensor integrated into firefighting gloves detected detailed finger angles and cyclic finger motions, demonstrating its capability for subtle human motion monitoring. It is also noteworthy that this novel strategy is a very quick, straightforward, and scalable method of fabricating strain sensors, which is extremely beneficial for practical applications.

Wearable Textile UHF-RFID Sensors: A Systematic Review

Textile radio-frequency identification operating in ultra-high frequency (UHF-RFID) sensors based on different scenarios are becoming attractive with the forthcoming internet of things (IoT) era and aging society. Compared with conventional UHF-RFID sensors, textile UHF-RFID sensors offer the common textile features, light weight, washability and comfort. Due to the short time and low level of development, researches on the integration of textile UHF-RFID techniques and textile sensing techniques are not flourishing. This paper is motivated by this situation to identify the current research status. In this paper, we provide a systematic review of the fundamentals of textile UHF-RFID sensors techniques, materials, the brief history and the state-of-the-art of the scenario-based development through detailed summary and analysis on the achievements from the starting year of 2004 to the present time. Moreover, according to the analysis, we give a proposal of the future prospects in several aspects, including the new materials and manufacturing processes, machine learning technology, scenario-based applications and unavoidable reliability.