Wireless Rehabilitation Training Sensor Arrays Made with Hot Screen-Imprinted Conductive Hydrogels with a Low Percolation Threshold

Abstract

Herein, we propose a highly sensitive wireless rehabilitation training ball with a piezoresistive sensor array for patients with Parkinson’s disease (PD). The piezoresistive material is a low percolation threshold conductive hydrogel which is formed with polypyrrole (PPy) nanofibers (NFs) as a conductive filler derived from a polydopamine (PDA) template. The proton acid doping effect and molecular template of PDA are essential for endowing PPy NFs with a high aspect ratio, leading to a low percolation threshold (∼0.78 vol %) and a low Young’s 004Dodulus of 37.69 kPa and hence easy deformation. The piezoresistive sensor exhibited a static and dynamic stability of 10,000 s and 15,000 cycle times, respectively. This stability could be attributed to the increased hydrophilicity of conductive fillers, enhancing the interfacial strength between the conductive filler and the matrix. The interaction between the PDA-PPy NFs and the hydrogel matrix endows the hydrogel with toughness and ensures the stability of the device. Additionally, the microdome structure of the conductive hydrogel, produced by hot screen-imprinting, dramatically improves the sensitivity of the piezoresistive sensor (∼856.14 kPa–1). The microdome conductive hydrogel can distinguish a subtle pressure of 15.40 Pa compared to the control hydrogel without a microstructure. The highly sensitive piezoresistive sensor has the potential to monitor the hand-grip force, which is not well controlled by patients with PD. The rehabilitation training ball assembled with a sensor array on the surface and a wireless chip for communication inside is built and used to monitor the pressure in real time through the WeChat applet. Thus, this work has significantly broadened the application of hydrogel-based flexible piezoresistive sensors for human activity monitoring, which provides a promising strategy to realize next-generation electronics.

Recent advances in flexible and soft gel-based pressure sensors

“…Thus, the active material should provide sufficient charge-transporting paths for current flow and the conducting network should adapt to various deformations with good elasticity. Piezoresistive pressure sensors not only possess high sensitivity, fast response speed and good stability, but also have a simple device structure and low manufacturing cost [79] . However, the necessity of an external power supply for resistance or current measurement with continuous resistance heating leads to low energy efficiency.…”

“…(D) Schematic illustrating the mechanism of a pressure sensor and photographs showing its installation at a specific position in the neck of a human subject for monitoring carotid artery and internal jugular vein pulses. Reproduced with permission [79] . Copyright 2022, The Author(s), published by Nature.…”

“…For example, Huang et al regenerated the silk fibroin into the graphene aerogel for applications as a capacitive sensor, which showed a much higher sensitivity of 0.73 kPa -1 (0.01-10.0 kPa) than that made of original graphene aerogel (~0.04 kPa -1 ) [156] . Shi et al prepared an aerogel by composing a conductive MXene with elastic polysiloxane [Figure 10D] [79] . Compressible multileveled channels were formed inside the microporous wall of the MXene due to the introduction of polysiloxane.…”

Flexible Pressure Sensors Based on Molybdenum Disulfide/Hydroxyethyl Cellulose/Polyurethane Sponge for Motion Detection and Speech Recognition Using Machine Learning

“…Among them, piezoresistive flexible pressure sensors are considered as ideal candidates for next-generation sensors due to their advantages of simple fabrication, easy signal reading, low energy consumption, and excellent static pressure detection capability. 16,17 To improve sensitivity, various sensor microstructures are designed and reported, such as pyramids, 18 domes 19 pillars, 20 and fibers. 21 However, because these sensors are difficult to fabricate and have a limited pressure detection range, their large-scale fabrication and practical application are limited.…”

“…In recent years, it has been widely used in the fields of wearable devices, , electronic skin, , human–machine interaction, , and health monitoring. − Due to the high-performance requirements of sensors in practical applications, flexible pressure sensors with different mechanisms such as piezoresistive, , capacitive, , and piezoelectric , have been widely studied. Among them, piezoresistive flexible pressure sensors are considered as ideal candidates for next-generation sensors due to their advantages of simple fabrication, easy signal reading, low energy consumption, and excellent static pressure detection capability. , To improve sensitivity, various sensor microstructures are designed and reported, such as pyramids, domes pillars, and fibers . However, because these sensors are difficult to fabricate and have a limited pressure detection range, their large-scale fabrication and practical application are limited .…”