Wearable Two-Dimensional Nanomaterial-Based Flexible Sensors for Blood Pressure Monitoring: A Review

Abstract

Flexible sensors have been extensively employed in wearable technologies for physiological monitoring given the technological advancement in recent years. Conventional sensors made of silicon or glass substrates may be limited by their rigid structures, bulkiness, and incapability for continuous monitoring of vital signs, such as blood pressure (BP). Two-dimensional (2D) nanomaterials have received considerable attention in the fabrication of flexible sensors due to their large surface-area-to-volume ratio, high electrical conductivity, cost effectiveness, flexibility, and light weight. This review discusses the transduction mechanisms, namely, piezoelectric, capacitive, piezoresistive, and triboelectric, of flexible sensors. Several 2D nanomaterials used as sensing elements for flexible BP sensors are reviewed in terms of their mechanisms, materials, and sensing performance. Previous works on wearable BP sensors are presented, including epidermal patches, electronic tattoos, and commercialized BP patches. Finally, the challenges and future outlook of this emerging technology are addressed for non-invasive and continuous BP monitoring.

Blood pressure measurement techniques, standards, technologies, and the latest futuristic wearable cuff-less know-how

“…Recently, wearable devices that can quickly and accurately measure BP have gained great attention towards early detection of hypertension. 13,14 In contrast to the conventional method, which records the information about blood pressure via auscultation or a sensor by applying external pressure, the wearable sensor network or device employs passive measurement and provides continuous beat-to-beat measurement as no external stimuli are applied. However, several of these technologies are under clinical validation and their commercialization is underway.…”

“…Previously, several review articles have been published that focused on the historical evolution of BP measurement techniques, instruments, and their calibration, 7 systematic approach in invasive techniques, 22 oscillometric BP measurement, 23 cuffless measurement techniques, 24,25 advances in non-invasive BP monitoring, 26,27 piezoelectric approach for BP monitoring, 28 and wearable two-and three-dimensional sensors for BP measurements. 13,14,29 Still, a comprehensive systematic study of the BP measurement techniques and the recently developed flexible and wearable technologies using these techniques is missing in the literature. Additionally, the validation of these developed wearable technologies from the universal standard is not discussed in the literature.…”

Recent Advances in Two-Dimensional Nanomaterials for Healthcare Monitoring

“…Conventional sensors comprising silicon or glass materials exhibit several limitations owing to their inflexible structures, bulky nature, and inability to constantly monitor essential health indicators such as blood pressure. 2D nanomaterials have garnered significant attention in flexible-sensor production owing to their advantageous characteristics, including a high surface-to volume ratio, excellent electrical conductivity, cost efficiency, flexibility, and lightweight. − …”

Rapid-Response and Highly Sensitive Piezocapacitive Pressure Sensor Based on Micro Buckling Periodic Layers for Wearable Applications

“…In the post-pandemic era and the artificial intelligence (AI) era, with the recent chat generative pretrained transformer rising explosively all over the world as a new milestone of AI, − the sharp development of both the virus and the intelligent science has aroused inspiring and further reflection among researchers on wearable electronics in the domain of wise information technology of med, − human–machine interaction, − and intelligent humanoid robots. , As a typical sensing component in the wearable system, a wearable pressure sensor can convert various pressures to processable electrical signals. − Compared with modern rigid pressure sensors, flexible pressure sensors show superior advantages, attributed to their elasticity, moldability, and portability features, more in line with the wearable needs. , Among various flexible pressure sensors based on different pressure sensing mechanisms, including piezoresistive, − piezocapacitive, − piezoelectric, − and triboelectric, − piezocapacitive pressure sensors have provoked researchers’ interest owing to their fast manufacture, low-cost preparation, scalable process, and fast response. , To meet the wearable requirements, all elements of the flexible capacitive pressure sensor, including conductive electrodes and the dielectric layer, are prepared based on an elastic substrate, like polydimethylsiloxane (PDMS), polyurethane, polyethylene glycol terephthalate, polyimide, and polyvinylidene difluoride . As a solution processable nanomaterial, silver nanowires (AgNWs) are one of the most promising conductive nanomaterials in fabricating flexible electrodes, due to its high electricity, excellent flexibility, and easy workability .…”

“…13−15 Compared with modern rigid pressure sensors, flexible pressure sensors show superior advantages, attributed to their elasticity, moldability, and portability features, more in line with the wearable needs. 16,17 Among various flexible pressure sensors based on different pressure sensing mechanisms, including piezoresistive, 18−20 piezocapacitive, 21−23 piezoelectric, 24−26 and triboelectric, 27−29 piezocapacitive pressure sensors have provoked researchers' interest owing to their fast manufacture, low-cost preparation, scalable process, and fast response. 30,31 To meet the wearable requirements, all elements of the flexible capacitive pressure sensor, including conductive electrodes and the dielectric layer, are prepared based on an elastic substrate, like polydimethylsiloxane (PDMS), polyurethane, polyethylene glycol terephthalate, polyimide, and polyvinylidene difluoride.…”