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.
Highlights
Sensors have been used for over 2000 years [1]
These advantages include the ease of fabrication of flexible sensors owing to the advancements in 3D printing methods and the ability to self-heal
Several examples of 3D printing methods that are currently used in manufacturing flexible sensors were discussed, including fused deposition modelling (FDM), FFF, inkjet printing, aerosol jetting, selective laser melting (SLM), direct ink writing (DIW), SLS and others
Summary
Sensors have been used for over 2000 years [1]. They can be defined as any device that can detect and react to changes in the surroundings. This review paper presents the most recent developments for the materials and methods used in the fabrication of flexible sensors. This review paper explores the limitations, advantages and advances in current methods and materials, including the use of additive manufacturing (3D printing) in the fabrication of these sensors. Various 3D printing methods being used in the fabrication of various types of flexible sensors including temperature, humidity, pressure, medical monitoring and chemical are explored. Most efforts in the research of flexible sensors are centred on enhancing the flexibility and conductivity of the materials used in the fabrication Areas such as robotics, prosthetics, implantable medical devices, electronic skin and smart watches require flexible and thin sensors. (c) Silver nanoparticles inkjet printed on paper to fabricate a flexible temperature sensor, sensor,reprinted reprintedwith withpermission permissionfrom from[14]. Various Types of Flexible Sensors (Temperature, Pressure, Humidity and Chemical)
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