A fast gelatinized asymmetric adhesive hydrogel for enhanced wearable sensor performance

Abstract

The application of wearable sensors is becoming increasingly widespread, among which hydrogels, with their excellent biocompatibility, multifunctionality and modulus similar to human skin, are considered one of the most promising wearable sensors. However, when using hydrogel flexible sensors adhering to human skin, unnecessary adhesion often occurs, resulting in operational difficulties and unstable signal collection. Moreover, the hydrogel polymerization process is time-consuming and difficult to perform. Based on this, we have prepared an asymmetric adhesive dual-layer conductive hydrogel that can be rapidly prepared to address the above issues. Introducing ZnCl₂ into a solution of tannic acid (TA) coated diatomaceous earth (DE) forms a self-catalytic system, allowing the hydrogel to be prepared within 15 seconds. The components ZnCl₂ and TA endow the system with lower freezing temperature and strong adhesion properties. By adjusting the ratio accordingly, a dual-layer hydrogel consisting of an asymmetrical structure could be prepared facilely. The adhesive side can firmly adhere to human skin and can be removed easily without leaving any residue, while the non-adhesive side can prevent it from sticking to fingers or clothing and contamination, facilitating stable signal transmission. The dual-layer hydrogel developed in this study possesses many advantages such as rapid gelation, asymmetric adhesion, strong interfacial force, mechanical reinforcement and anti-freezing properties. It can stably monitor a wide range of strains and daily human movements, with broad application prospects, providing a new approach for the development of functional flexible devices.