Bidirectional and Stretchable Piezoresistive Sensors Enabled by Multimaterial 3D Printing of Carbon Nanotube/Thermoplastic Polyurethane Nanocomposites

Abstract

Fabricating complex sensor platforms is still a challenge because conventional sensors are discrete, directional, and often not integrated within the system at the material level. Here, we report a facile method to fabricate bidirectional strain sensors through the integration of multiwalled carbon nanotubes (MWCNT) and multimaterial additive manufacturing. Thermoplastic polyurethane (TPU)/MWCNT filaments were first made using a two-step extrusion process. TPU as the platform and TPU/MWCNT as the conducting traces were then 3D printed in tandem using multimaterial fused filament fabrication to generate uniaxial and biaxial sensors with several conductive pattern designs. The sensors were subjected to a series of cyclic strain loads. The results revealed excellent piezoresistive responses with cyclic repeatability in both the axial and transverse directions and in response to strains as high as 50%. It was shown that the directional sensitivity could be tailored by the type of pattern design. A wearable glove, with built-in sensors, capable of measuring finger flexure was also successfully demonstrated where the sensors are an integral part of the system. These sensors have potential applications in wearable electronics, soft robotics, and prosthetics, where complex design, multi-directionality, embedding, and customizability are demanded.

A review of flexible force sensors for human health monitoring

“…9 a) [77] or integrated it on a glove-like device ( Fig. 9 b) [47] . When the finger was bent, straightened or coordinated moved with the fingers, the deformation of sensor would cause changes in the internal resistance or other electrical parameters.…”

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Fig. 9 (a) The change of the resistance of the wearable sensor under different bending degrees of the finger, that is, the change of the brightness of the LED [77] ; (b) Schematic diagram of the change in the extension of the glove-type wearable sensor [47] ;(c) The sensor collecting throat muscle movement signals [81] ;(d) The image of the plantar sensor array [83] .

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Fused Filament Fabrication of Piezoresistive Carbon Nanotubes Nanocomposites for Strain Monitoring

“…Among these three factors, the first two are most likely the most influential on the electrical resistance upon mechanical deformation (Georgousis et al, 2015). The common matrices used for strain sensor materials can be thermosetting (Ku-Herrera and Avilés, 2012;Moriche et al, 2016b;Sanli et al, 2016), thermoplastics (Georgousis et al, 2015;Bautista-Quijano et al, 2016;Dawoud et al, 2018), and elastomers (Bautista-Quijano et al, 2010Oliva-Avilés et al, 2011;Alsharari et al, 2018;Christ et al, 2019;Kim et al, 2019).…”

Stretchable, Patch‐Type Calorie‐Expenditure Measurement Device Based on Pop‐Up Shaped Nanoscale Crack‐Based Sensor

“…For instance, a wearable form of strain gauge that can precisely monitor large‐scale and rapid motion would measure physical activity by relating the amplitude and speed of the angular movement in a target joint. Recent advances in flexible and stretchable electronics created research opportunities in applying strain gauges to the human body . Stretchable carbon nanotube strain sensors attached to various parts of the body could detect human motions with high durability, fast response, and low creep .…”