Highly Transparent, Self-Healing, and Self-Adhesive Double Network Hydrogel for Wearable Sensors.

Kai Chen,Pei Liu,Xiufeng Xiao,Qian Feng,Yongsheng Yu,Feng Wang,Qianqian Du,Yunping Hu,Cong Li,Mingxiang Liu

doi:10.3389/fbioe.2022.846401

Abstract

Hydrogel-based flexible electronic devices are essential in future healthcare and biomedical applications, such as human motion monitoring, advanced diagnostics, physiotherapy, etc. As a satisfactory flexible electronic material, the hydrogel should be conductive, ductile, self-healing, and adhesive. Herein, we demonstrated a unique design of mechanically resilient and conductive hydrogel with double network structure. The Ca2+ crosslinked alginate as the first dense network and the ionic pair crosslinked polyzwitterion as the second loose network. With the synthetic effect of these two networks, this hydrogel showed excellent mechanical properties, such as superior stretchability (1,375%) and high toughness (0.57 MJ/m3). At the same time, the abundant ionic groups of the polyzwitterion network endowed our hydrogel with excellent conductivity (0.25 S/m). Moreover, due to the dynamic property of these two networks, our hydrogel also performed good self-healing performance. Besides, our experimental results indicated that this hydrogel also had high optical transmittance (92.2%) and adhesive characteristics. Based on these outstanding properties, we further explored the utilization of this hydrogel as a flexible wearable strain sensor. The data strongly proved its enduring accuracy and sensitivity to detect human motions, including large joint flexion (such as finger, elbow, and knee), foot planter pressure measurement, and local muscle movement (such as eyebrow and mouth). Therefore, we believed that this hydrogel had great potential applications in wearable health monitoring, intelligent robot, human-machine interface, and other related fields.

Highlights

Conventional semiconductor-based strain sensors have limitations in the generation of electronics due to their inherent deficiencies (Liu et al, 2020), including brittleness, rigidity, and low biocompatibility (Zhang et al, 2022)
Our research demonstrated that our ADN hydrogel could work well as a wearable strain sensor directly to respond to a variety of large joint flexion and local muscle movement
In order to avoid the formation of a heterogeneous network due to the rapid ion release process, we chose the (EDTANa2Ca)/D(+)-gluconic acid δ-lactone (GDL) system to delay the Ca2+ release during the alginate-Ca2+ crosslinking formation (Akay et al, 2017; Yang et al, 2021)

Summary

INTRODUCTION

Conventional semiconductor-based strain sensors have limitations in the generation of electronics due to their inherent deficiencies (Liu et al, 2020), including brittleness, rigidity, and low biocompatibility (Zhang et al, 2022). Excellent tensile property makes hydrogel-based wearable devices suitable for large strain of human body, expanding the application range of sensors (Sun et al, 2021). A novel conductive double network hydrogel was prepared by a one-pot and two-step procedure This hydrogel was synthesized by an alginate network physically cross-linked by calcium ions and interpenetrating copolymers consisting of anionic monomer sodium p-styrene sulfonate (NAS) and cationic monomer acryloxyethyl trimethyl ammonium chloride (DAC) (Figure 1). During the monitoring of human movements, the wearable strain sensor was directly attached to the volunteers’ skin, and the real-time change of the resistance of the sensor was recorded with an LCR meter. P-value was lower than 0.05, the difference was considered significant

Design Principles and Material Synthesis

CONCLUSION

ETHICS STATEMENT