Materials, Electrical Performance, Mechanisms, Applications, and Manufacturing Approaches for Flexible Strain Sensors

Abstract

With the recent great progress made in flexible and wearable electronic materials, the upcoming next generation of skin-mountable and implantable smart devices holds extensive potential applications for the lifestyle modifying, including personalized health monitoring, human-machine interfaces, soft robots, and implantable biomedical devices. As a core member within the wearable electronics family, flexible strain sensors play an essential role in the structure design and functional optimization. To further enhance the stretchability, flexibility, sensitivity, and electricity performances of the flexible strain sensors, enormous efforts have been done covering the materials design, manufacturing approaches and various applications. Thus, this review summarizes the latest advances in flexible strain sensors over recent years from the material, application, and manufacturing strategies. Firstly, the critical parameters measuring the performances of flexible strain sensors and materials development contains different flexible substrates, new nano- and hybrid- materials are introduced. Then, the developed working mechanisms, theoretical analysis, and computational simulation are presented. Next, based on different material design, diverse applications including human motion detection and health monitoring, soft robotics and human-machine interface, implantable devices, and biomedical applications are highlighted. Finally, synthesis consideration of the massive production industry of flexible strain sensors in the future; different fabrication approaches that are fully expected are classified and discussed.

Silver Nanowires in Stretchable Resistive Strain Sensors

“…The three primary mechanisms by which the increase in resistance upon the application of strain is achieved are crack propagation, disconnection/reconnection, and tunneling effects [ 13 ]. In the case of strain sensors with a nanomaterial thin film coated on a flexible substrate, the principal mechanism of the increase in resistance is based on the propagation of cracks [ 35 ].…”

“…For example, Amir Servati et al presented a review on novel flexible and wearable electronic materials and sensors suitable for monitoring vital human signs [ 11 ]. Yan Liu et al [ 12 ] and Fei Han et al [ 13 ] reviewed the advances in flexible strain sensors, focusing on materials, mechanisms, applications, and manufacturing strategies. Few other reviews elucidate the progress in this type of sensor from the angle of filling elements, i.e., carbon-based nanomaterials [ 14 ], metal nanowires [ 15 ], and conducting polymers [ 16 ].…”

Challenges and limitation of wearable sensors used in firefighters’ protective clothing

“…In addition, to gain optimal performance, they should have some essential features, such as reasonable flexibility, lightweight, adequate stretchability, and biocompatibility. [14][15][16][17] Therefore, selecting suitable substances and techniques for the flexible sensor fabrication is of great importance.…”

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.…”

“…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. Han et al [6] discussed the materials, fabrication methods and electrical performance of flexible strain sensors. The sensitivity, linearity, response time and durability properties of the sensors were captured.…”