Flexible and Stretchable Electronic Skin with High Durability and Shock Resistance via Embedded 3D Printing Technology for Human Activity Monitoring and Personal Healthcare

Abstract

Electronic skin (e‐skin) integrating pressure sensors and strain sensors has shown great potential applications in smart robotics and healthcare monitoring for their flexibility and wearability. However, making the sensor low cost and highly durable for industrialization and commercialization is still a problem to be addressed. An embedded 3D printing technology is developed based on novel thermosetting printing ink which is prepared using the Ecoflex and carbon nanoparticles. The properties of the printing ink including printability and electrical conductivity are first studied and then optimized. By using this technology, a glove‐shaped e‐skin integrating both strain sensors and pressure sensors is fabricated, and the properties of the sensors are studied. Both types of sensors have excellent stability and reliability which are verified by multiple long‐term measurements (10 000 testing cycles). Specifically, the sensors possess a great shock resistance and high durability which are significant for application in real life. Furthermore, some applications for human activity monitoring and personal healthcare are demonstrated, including complex gesture recognition using 15 strain sensors, hardness sensing using pressure sensors coupled with strain sensors, and arterial pulse measurement using pressure sensors, which are promising for smart robotic sensing and wearable biomedical devices.

Biocompatible and Highly Stretchable PVA/AgNWs Hydrogel Strain Sensors for Human Motion Detection

“…Flexible and stretchable sensors are attracting significant interest in a wide range of applications including health monitoring, diagnostic devices, soft robotics, and electronic skins. [ 1–6 ] Piezoresistive sensors, one of the main types of sensors, change their resistance in response to mechanical deformation and have demonstrated a number of applications in monitoring strain, [ 4–8 ] pressure, [ 6,7,9 ] flow, [ 10–12 ] and temperature. [ 4,13,14 ] To meet the requirements for both human motion detection and biosafety, flexible sensors should be biocompatible.…”

“…In this regard, different types of elastomers such as polydimethylsiloxane (PDMS) or hydrogels such as polyvinyl alcohol (PVA) hydrogels have been extensively used as the flexible substrate/matrix. [ 15–18 ] While the flexible substrate/matrix, in most cases, determines the mechanical properties of the sensors, conductive materials including carbon nanoparticles, [ 6 ] carbon nanofibers (CNFs), [ 15,19 ] carbon nanotubes (CNTs), [ 20 ] graphene, [ 5,21 ] silver nanowires (AgNWs), [ 19,22 ] and silver nanoparticles [ 23 ] have been successfully used as the sensing elements. Different techniques have been developed to incorporate conductive elements with the flexible substrate/matrix.…”

Progress in wearable electronics/photonics—Moving toward the era of artificial intelligence and internet of things

“…Flexibility, stretchability and light‐weight of wearable electronics, as the key factors determining the comfort level of users and the portability of devices, have drawn tremendous attention across the world for developing finger/glove sensors with such characteristics 122‐125 . The common flexible strain sensors are normally based on resistive sensing 123,126‐137 or capacitive sensing, 138,139 whose output signals can dynamically respond to the variation of applied force or strain under continuous motions. A finger‐bending strain sensor is presented using stretchable gallium‐based conductors, as indicated in Figure 3C 140 .…”

A wearable motion capture device able to detect dynamic motion of human limbs

“…And the measurement equation is therefore established as shown in Eq. (20). υ 1 and υ 2 are measurement noises (assumed as white Gaussian noises) of the micro velocity sensors and the accelerometer, respectively, having zero mean and standard deviation σ υ1 and σ υ2 , respectively.…”