3D Printed Flexible Strain Sensors: From Printing to Devices and Signals

Abstract

The revolutionary and pioneering advancements of flexible electronics provide the boundless potential to become one of the leading trends in the exploitation of wearable devices and electronic skin. Working as substantial intermediates for the collection of external mechanical signals, flexible strain sensors that get intensive attention are regarded as indispensable components in flexible integrated electronic systems. Compared with conventional preparation methods including complicated lithography and transfer printing, 3D printing technology is utilized to manufacture various flexible strain sensors owing to the low processing cost, superior fabrication accuracy, and satisfactory production efficiency. Herein, up-to-date flexible strain sensors fabricated via 3D printing are highlighted, focusing on different printing methods based on photocuring and materials extrusion, including Digital Light Processing (DLP), fused deposition modeling (FDM), and direct ink writing (DIW). Sensing mechanisms of 3D printed strain sensors are also discussed. Furthermore, the existing bottlenecks and future prospects are provided for further progressing research.

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

“…Wearables have gained much attention in the last decade [11,48,[98][99][100][101][102][103][104]. These are electronic devices that are attached to the human body, a typical example being smart watches that had an estimated global market share of over 20 billion USD in 2019, 59 billion USD in 2021 and is predicted to rise to 96 billion USD by 2027 [8,9,103,104].…”

“…Privacy issues, performance risks and social risks are other noted areas for future investigation [102]. Furthermore, regarding the materials research needs, nanomaterials have gained much attention due to the advanced physicochemical properties and the need to miniaturise wearables [11,41,48,98,99].…”

“…Furthermore, regarding the materials research needs, nanomaterials have gained much attention due to the advanced physicochemical properties and the need to miniaturise wearables [11,41,48,98,99]. Three-dimensional printing is currently and will continue to play an important role in the development of wearables (and sensors in general) due to its ability to customise devices easily, achieve designs not possible via other techniques, reduce or avoid assembly operations, as well as the use of multi-material composites with advanced electrical/mechanical properties [56,59,102]. Wearable sensors and their characteristics are summarised in Table 5.…”

Thermal Characterization of New 3D-Printed Bendable, Coplanar Capacitive Sensors

“…Growing interest has emerged over the last few years in the field of 3D-printed flexible sensors: AM-based technologies seem to fit very well with the sensors’ requirements, leading to several advantages from a manufacturing point of view (i.e., reduction in the number of assembly tasks, huge geometric freedom, etc.). Extrusion-based methods are mainly used to fabricate flexible and wearable sensors based on piezoresistive effects [ 22 ], where movements are detected by a change in resistance. Generally, 3D-printed wearable sensors are used to measure quantities related to human body movements such as knee bending, hand movements, etc.…”

Additive Manufacturing as a Means of Gas Sensor Development for Battery Health Monitoring

“…Sharafeldin et al [1] pointed out that 3D printing is very promising even for the detection of cancer and other diseases, because these complex diagnostic devices could be simply connected to portable devices like smartphones with batteries [1]. Also the fabrication of strain sensors by 3D printing has been demonstrated by Liu et al [8] using various printing methods, such as Digital Light Processing (DLP) and Direct Ink Writing (DIW) [8]. Han et al [9] presented an overview of the challenges of current biomedical sensors [9].…”