Carbon-Based, Ultraelastic, Hierarchically Coated Fiber Strain Sensors with Crack-Controllable Beads

Abstract

Fiber-based electronics or textronics are spotlighted as a promising strategy to develop stretchable and wearable devices for conformable machine–human interface and ubiquitous healthcare systems. We have prepared a highly sensitive fiber-type strain sensor (maximum gauge factor (GF) = 863) with a broad range of strain (ε < 400%) by introducing a single active layer onto the fiber. In contrast to other metal-based fiber-type electronics, our hierarchical fiber sensors are based on coating carbon-based nanomaterials with responsive microbeads onto elastic fibers. Utilizing the formation of uniform cracks around the microbeads, the device performance was maximized by adjusting the number of microbeads in the carbon-coating layer. We overcoated the carbon-based coating layer of the elastic fiber with a protective polymeric layer and verified no effects on the GF and the range of strain. Our fiber sensors were repeatedly tested more than 5000 times, exhibiting excellent cyclic responses to on/off switching behaviors. For practical applications, the hierarchical fiber sensors were sewed into electrical fabric bands, which are integrable to a wireless transmitter to monitor waveforms of pulsations, respirations, and various postures of level of bending a spinal cord.

The E-Textile for Biomedical Applications: A Systematic Review of Literature

“…Quite recently, the research on blood pulse monitoring has gained increasing importance, as testified by the growing number of contributions appeared in the literature. For instance, Jang et al [ 38 ] developed a composite fiber sensor which was later sewed in an electric armband applied, in turn, on an artificial arm with varied blood pressures. The experiment on this artificial setup demonstrated the system was capable to distinguish rachial artery pulses with varying blood pressure and pulse rate.…”

“…Jang et al [ 38 ] proposed a highly sensitive fiber-type strain sensor with a broad range of strain by introducing a single active layer onto the fiber. The sensors were sewn into electrical fabric bands, which are integrable to a wireless transmitter to monitor waveforms of pulsations, respirations, and various postures of level of bending a spinal cord.…”

“…It is not by chance if Ferreira et al [ 15 ] investigated—using their custom-made chest belt and the Baby Night Watch IT platform (see also Section 3.1 )—respiratory rate variations in infants to monitor eventual Sudden Infant Death Syndrome events; nevertheless, albeit the chest belt represents for all intents and purposes an e-textile system, respiratory rate was acquired by the authors using a triaxial accelerometer integrated in the chest belt, differently from the ECG signal. An e-textile embedded chest belt was developed even by Jang et al [ 38 ]. Specifically, the authors sewed horizontally on the chest belt the same composite fiber sensor (developed even for pulse acquisition), aiming at monitoring respiratory waveforms from an HC in various breathing conditions.…”

Functionalized Fiber-Based Strain Sensors: Pathway to Next-Generation Wearable Electronics

“…Increased encapsulation thickness can guarantee good robustness but result in inconsistent compliance between encapsulation and sensing elements, which may deteriorate sensing reliability. Much research in recent years has focused on the relation between strain-caused cracks and the detection capability of strain sensors due to their outstanding sensitivity [145][146][147][148]. The unmatched mechanical properties between the fiber-based conductive elements and elastomers lead to functional cracks during strain deformation, further inducing the resistance increase.…”

“…Copyright © 2018 Wiley-VCH. e Fabrication illustration of hierarchical strain sensor with spandex fiber substrate, coating of beaded carbon nanomaterials, and Ecoflex encapsulated layer [145]. Copyright © 2019 American Chemical Society.…”