High Sensitivity, Broad Working Range, Comfortable, and Biofriendly Wearable Strain Sensor for Electronic Skin

Abstract

coupled with an ultrabroad measuring range (2800%). Notwithstanding, the corresponding gauge factor (GF, known as the sensor sensitivity metric, GF = ΔR/R 0 ε, where ΔR denotes the change in resistance during stretching, R 0 represents the resistance before stretching, and strain is represented by ε.) is ≈16.9, indicating that the sensitivity of the sensor is poor and it may not be able to detect small strains. [18] Alternatively, inspired by the microcracks on the surface of spider legs, Robert et al. prepared similar cracks in the conductive film, which provided the sensor with outstanding sensitivity (GF = 2000) and could detect very small deformations. Unfortunately, the narrow measurement range (2%) of the sensor limits its widespread practical application. [19] Sensitivity and stretchability are two influential indicators of the performance of stretchable strain sensors. In general, ultrahigh sensitivity requires the sensing material to achieve substantial structural changes even under slight strain, whereas large stretchability requires the sensing material to have structural connections or complete morphology during large deformations. [20][21][22] Although much effort has been devoted toward optimizing them, it is still difficult to produce sensors with remarkable sensitivity and stretchability. [23][24][25][26][27][28][29] High sensing performance is important for perfect wearable strain sensors. However, the processing technology and wearing experience of strain sensors, which have received inadequate attention, are equally important. Considering long-term contact with the skin or tissues for health monitoring, more research is needed to improve sensor comfort, safety, and health. [30][31][32] Furthermore, the preparation process for fabricating resistancetype strain sensors, such as dip-coating, [33] spin-coating, [34] and vacuum filtration, always requires complex steps, [35] expensive equipment, and harsh conditions, which are detrimental to their practical application, resulting in the inability to quickly mass-produce. Although considerable achievements have been realized in each field, there are still significant challenges in designing a stretchable strain sensor that possesses the characteristics of excellent sensitivity, super-stretchability, comfort, safety, and low cost using a simple and fast method. [36,37] In this study, we used electrospinning to fabricate a thermoplastic polyurethane (TPU) nanofiber film with high stretchability, waterproofness, and breathability as flexible substrates for wearable strain sensors. Thereafter, we used screen

Toward a new generation of permeable skin electronics

“…The sensors achieved great air permeability (80 mm s −1 ), impressive stretchability (GF = 520), and a wide operating range (up to 500% strain). 225 Wang et al reported a breathable strain sensor based on carbonized silk fabrics. The original silk fabric was carbonized by heat treatment under an inert atmosphere and then further encapsulated (Fig.…”

Self-Adhesive, Antifreezing, and High Resilience Biobased Ionogel as a Flexible Strain–Temperature Bimodal Sensor

“…The progress in wearable sensor technology owes much to the evolution of flexible electronic devices. − Among these, strain sensors stand out for their lightweight, remarkable sensitivity, and stretchability, making them ideal for easy attachment to human skin to capture electrical signals originating from human activities. To accomplish this, for conventional strain sensors, conductive fillers like carbon nanotubes, graphene, and polyaniline are incorporated into flexible substrate materials. − However, the mismatched modulus between rigid conductive fillers and soft elastic substrates often results in reduced transparency and is prone to interface delamination, leading to decreased durability. − To address these challenges, ionic conductive sensors have emerged as a promising substitute for electronic conductive sensors in recent times, including ionic hydrogels and ionogels. , Nevertheless, the mechanical performance deterioration and stability issues caused by the freezing and drying of ionic hydrogels have not been effectively resolved. In contrast, ionogels inherit the characteristics of ionic liquids, such as high-temperature stability and freeze resistance, making them ideal alternatives for hydrogels. − Furthermore, the intrinsic humidity and temperature sensitivity of ionic liquids also confer multifunctionality to ionogels, enabling them to possess strain-sensing, temperature-monitoring, and humidity-detection capabilities. − …”

Tough, anti-drying and thermoplastic hydrogels consisting of biofriendly resources for a wide linear range and fast response strain sensor

“…9,10 Many recent studies focus on enhancing their sensitivity and stretchability to have a wider working range. [11][12][13][14] However, as their working range is extended, nonlinearity, which is one of the fundamental drawbacks of resistive sensors, becomes increasingly severe. 15 The linearity of a strain sensor refers to the positive correlation between the output signal and the applied strain.…”