Textile‐Enabled Highly Reproducible Flexible Pressure Sensors for Cardiovascular Monitoring

Abstract

signal-related monitoring, such as cuffless blood pressure (BP) measurement, [7] pulse wave velocity (PWV) estimation, [8] and pulse phase diagram analysis, sensors should be specifically engineered to record epidermal pulse signals with explicit details and without signal distortions. [3] While the requirements on sensor flexibility, sensitivity, and linear range may be adjusted according to different applications, there are two sensor properties that are always in demand-high repeatability and one-to-one correspondence between pressure input and electrical output (i.e., no loading-unloading hysteresis). Sensor repeatability refers to the reproducibility of the pressure response in multiple cycles, over multiple days, and among multiple sensors. Since the pressure readings of a sensor are extracted from an initially calibrated pressure input-electrical output relation, it is essential for the sensor to maintain this relation throughout its lifetime in order to achieve good measurement accuracy and reliability. Also, for scaled up applications such as sensor networks and sensor arrays, variations in individual sensor characteristics should be minimized to reduce the computational load of signal processing. Repeatability it has been a main issue that prohibits the use of many flexible pressure sensors in practical applications. However, fundamental mechanisms that cause fluctuated sensor performance have not been well understood, and new material strategies to provide high sensor repeatability are yet to be developed.In this work, we explored the potential of using knitted fabrics to achieve high repeatability and hysteresis-free pressure responses in FPS systems. The knitted fabric materials are Flexible piezoresistive sensors (FPS) with high reproducibility and hysteresisfree pressure response are highly desirable for various emerging biomedical applications. In this work, the potential of using regularly interlaced textile materials to achieve high-repeatability and low-hysteresis FPS is explored. It is found that the structural flexibility and surface regularity of knitted fabric structures can in general provide reproducible pressure response; however, response fluctuations and hysteresis are still present due to the inevitable inelastic deformation of the textiles. To address this limitation, carbon black particles and polyvinylidene fluoride are introduced in the knitted fabric as the electrical and mechanical interconnects, respectively, between the fibers. Through composition optimization, the pressure response variation is reduced to below 2% and the hysteresis loop deviation is decreased to below 10% for single sensors. The performance variation among multiple sensors is as low as 5%, much smaller than the 33% variation of the sensors made with nonwoven fabrics. Utilizing the high sensor repeatability, sensor arrays and multisite sensor network are successfully realized for monitoring superficial temporal artery pulse pressure and pulse wave velocity, which demonstrate the potential of using wearable s...

Highly sensitive pressure sensor based on structurally modified tissue paper for human physiological activity monitoring

“…The time between P2 and P1 (Δ T DVP ) is also one of the evaluation parameters of pulse condition. Δ T DVP value is about 0.27 second, conform to the normal range of other literature reports …”

“…So far, researchers have developed pressure sensors based on different pressure response modes (sensing types), such as piezoresistive, piezoelectric, capacitive, and transistor . Among them, the piezoresistive pressure response mode shows great application prospects due to the simplicity of its sensing mechanism and the tractability of the signal.…”

Wearable Sensing and Telehealth Technology with Potential Applications in the Coronavirus Pandemic

“…Cuffless continuous monitoring approaches can be implemented into wearable and unobtrusive devices, such as watch [121], glasses [122,123], a wrist/armband [99,124,125], shirt [126], sleeping cushion [127], chair [128], smartphone [112], camera and flexible patch [114,129,130] as summarized in Fig. 8.…”

“…Twenty-four hour unobtrusive continuous BP monitoring can be equipped with flexible sensing, which may use a single skinlike patch [129,130], or even a skin-like sensor that can also potentially address the issue of motion artefact [131]. Alternatively, a ring-typed device [132] provides a promising approach for long-term continuous monitoring due to its small size.…”

Human Motion Recognition of Knitted Flexible Sensor in Walking Cycle

“…Flexible conductive materials can potentially be applied in human motion sensors, health monitoring for medical monitoring systems such as respiratory rate, heart rate and body posture to human-machine interface and wearable integrated devices that have attracted widespread attention [1][2][3][4][5][6][7][8][9][10]. Most common flexible sensors are made of conductive metal nanoparticles, metal films, carbon nanotubes and graphene [11,12]. Every material has its own conductivity; however, their working strain range is small and thus limits their practical application [8,13,14].…”