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

Abstract

The use of flexible sensors has tripled over the last decade due to the increased demand in various fields including health monitoring, food packaging, electronic skins and soft robotics. Flexible sensors have the ability to be bent and stretched during use and can still maintain their electrical and mechanical properties. This gives them an advantage over rigid sensors that lose their sensitivity when subject to bending. Advancements in 3D printing have enabled the development of tailored flexible sensors. Various additive manufacturing methods are being used to develop these sensors including inkjet printing, aerosol jet printing, fused deposition modelling, direct ink writing, selective laser melting and others. Hydrogels have gained much attention in the literature due to their self-healing and shape transforming. Self-healing enables the sensor to recover from damages such as cracks and cuts incurred during use, and this enables the sensor to have a longer operating life and stability. Various polymers are used as substrates on which the sensing material is placed. Polymers including polydimethylsiloxane, Poly(N-isopropylacrylamide) and polyvinyl acetate are extensively used in flexible sensors. The most widely used nanomaterials in flexible sensors are carbon and silver due to their excellent electrical properties. This review gives an overview of various types of flexible sensors (including temperature, pressure and chemical sensors), paying particular attention to the application areas and the corresponding characteristics/properties of interest required for such. Current advances/trends in the field including 3D printing, novel nanomaterials and responsive polymers, and self-healable sensors and wearables will also be discussed in more detail.

Helicobacter Pylori-Induced Gastric Infections: From Pathogenesis to Novel Therapeutic Approaches Using Silver Nanoparticles

“…The principal effect was represented by damage of bacterial enzymes in glycolysis and tricarboxylic acid cycle determining the stalling of the oxidative branch of the tricarboxylic acid cycle. Furthermore, an article published in 2019 confirmed that silver ions target glyceradldehyde-3-phosphate dehydrogenase in glycolysis in E. coli [105,106].…”

“…The principal effect was represented by damage of bacterial enzymes in glycolysis and tricarboxylic acid cycle determining the stalling of the oxidative branch of the tricarboxylic acid cycle. Furthermore, an article published in 2019 confirmed that silver ions target glyceradldehyde-3-phosphate dehydrogenase in glycolysis in E. coli [ 105 , 106 ]. The potential action of silver ions against bacteria should be taken into consideration as a better antimicrobial alternative treatment reducing the risk of antibiotic resistance.…”

Mixed-Dimensional MXene Nanocomposites/Aramid Nanofibers-Based Flexible Pressure and Strain Sensor for Electronic Skin

“…Flexible sensors with force sensing are highly favored by researchers due to the potentially huge applications in robotics, health and medicine, and artificial intelligence . Flexible sensors based on novel nanomaterials and flexible materials are meeting the emerging need, as the mechanical properties of flexible materials and the high sensitivity of nanomaterials can break the upper limit of deformation to better achieve perfect contact on irregular surfaces …”

Recent advances in the 3D printing of electrically conductive hydrogels for flexible electronics

“…[19][20][21][22] Up to now, there has been a lot of research effort spent trying to resolve the above challenges. [23][24][25][26] For instance, various 3D printing techniques (ink-based and light-based) have been applied in printing conductive hydrogels, offering more options for the customized application. Abundant material synthesis routes have been proposed to prepare printable hydrogels with good conductivity, stretchability, and functionality.…”