Advanced Flexible Skin-Like Pressure and Strain Sensors for Human Health Monitoring

Abstract

Recently, owing to their excellent flexibility and adaptability, skin-like pressure and strain sensors integrated with the human body have the potential for great prospects in healthcare. This review mainly focuses on the representative advances of the flexible pressure and strain sensors for health monitoring in recent years. The review consists of five sections. Firstly, we give a brief introduction of flexible skin-like sensors and their primary demands, and we comprehensively outline the two categories of design strategies for flexible sensors. Secondly, combining the typical sensor structures and their applications in human body monitoring, we summarize the recent development of flexible pressure sensors based on perceptual mechanism, the sensing component, elastic substrate, sensitivity and detection range. Thirdly, the main structure principles and performance characteristic parameters of noteworthy flexible strain sensors are summed up, namely the sensing mechanism, sensitive element, substrate, gauge factor, stretchability, and representative applications for human monitoring. Furthermore, the representations of flexible sensors with the favorable biocompatibility and self-driven properties are introduced. Finally, in conclusion, besides continuously researching how to enhance the flexibility and sensitivity of flexible sensors, their biocompatibility, versatility and durability should also be given sufficient attention, especially for implantable bioelectronics. In addition, the discussion emphasizes the challenges and opportunities of the above highlighted characteristics of novel flexible skin-like sensors.

Recent Advances in Wearable Optical Sensor Automation Powered by Battery versus Skin-like Battery-Free Devices for Personal Healthcare—A Review

“…Most commercially available wearable gadgets are mechanically hard components attached to bands and worn on the wrist, with form factors eventually constrained by the size and weight of the batteries required for the power supply. Wearable gadgets with “skin-like” qualities are a new kind of automation that is only starting to make its way out of research labs and into pre-commercial prototypes [ 119 , 120 ]. The use of near-field communication (NFC) automation for multicolor light emission and recognition in a way that permits accurate evaluation of the optical features of the skin—to detect peripheral vascular disease (PVD) and assess coloration—and/or of color-responsive materials for environmental discovery, is demonstrated in several battery-free, wireless OE devices.…”

Alkyl Chain Length Effects of Imidazolium Ionic Liquids on Electrical and Mechanical Performances of Polyacrylamide/Alginate-Based Hydrogels

“…Stretchable, flexible, wearable and environmentally friendly electronic devices are of great significance to meet the increasing demands for versatility and complexity of modern electronics [1][2][3][4][5][6][7][8]. The strain sensors have attracted tremendous attention recently since they can convert mechanical deformations into electrical signals, and they are widely used in personalized healthcare [9,10], human-machine interaction [11][12][13], human motion detection [14,15], physiological monitoring [16,17], electronic skins [18][19][20][21][22], artificial intelligence [23] and so on. Most conventional strain sensors fabricated by metals, semiconductors and carbon-based materials only can sense small deformations of less than 5% strain [24] and have poor recoverability, making them uncomfortable to wear and difficult to get used to.…”

Review of Materials and Fabrication Methods for Flexible Nano and Micro-Scale Physical and Chemical Property Sensors

“…According to the review paper [3], the market share of flexible displays was 8% in 2016 and rose to 27% by 2020, corresponding with the recent rapid growth of this research area. There are other review papers on flexible sensors published within the last 2 years [3][4][5][6][7], showing rapid growth of this research topic. One report published in 2020 [4] reviewed 3D printed sensors covering force sensors, pressure sensors and others.…”

“…The report did not capture other manufacturing methods or the use of nanomaterial in depth. Another report published in 2021 [5] concentrated on flexible pressure and strain sensors used in health monitoring. They covered the sensing mechanisms and the use of nanomaterials such as carbon nanotubes in depth, however they did not cover manufacturing methods such as 3D printing which has recently gained much attention for polymer processing.…”