웨어러블 센서용 고신축성, 접착성, 이온전도성 투명 하이드로겔

Abstract

Hydrogels are three-dimensional polymeric networks with hydrophilic properties, enabling them to absob and retain significant amounts of water. Their flexibility and biocompatibility make them suitable for a wide range of applications, including biosensors, wearable devices, and drug delivery systems. Notably, their ability to respond sensitively to external environmental changes enhances their potential as smart materials. However, conventional hydrogels often suffer from limitations such as low mechanical strength, poor stretchability, and insufficient electrical properties, which restrict their use in advanced applications. In this study, we addressed these limitations by doping HPMC/PAM-based hydrogels with lithium chloride (LiCl) to simultaneously enhance their ionic conductivity and physical properties. LiCl doping significantly improved the hydrogel's moisture retention, as the LiCl-doped hydrogel, stored under refrigeration, maintained moisture for up to 200 hours, while the undoped sample lost nearly 80% of its moisture over the same period. This highlights the crucial role of LiCl doping in stabilizing the hydrogel's water content under various environmental conditions. Additionally, LiCl doping notably enhanced the mechanical properties of the hydrogel. The doped hydrogel exhibited a 24% increase in adhesion strength on paper substrates, a tensile strength of 47 kPa, and a maximum strain of 1123%, resulting in a 3.5-fold increase in toughness. After doping with 7M LiCl, the hydrogel achieved an ionic conductivity of 16.05 S/m, representing a 32-fold improvement compared to the undoped sample. Furthermore, the hydrogel displayed an optical transmittance of approximately 80% in the visible light range. The wearable sensors fabricated from the LiCl-doped hydrogel reliably detected various body movements, such as finger bending and wrist motion, with rapid reponse times of 80ms for bending and 60ms for straightening. These results demonstrate that the HPMC/PAM/LiCl hydrogel is a promising material for applications in wearable sensors and healthcare monitoring systems.