Skin-Mountable Thermo-responsive Structured Hydrogel for Optical and Adhesion Coupled Functional Sensing

Smart hydrogel sensors with intrinsic responsiveness, such as pH, temperature, humidity, and other external stimuli, possess broad applications in innumerable fields such as biomedical diagnosis, environmental monitoring, and wearable electronics. However, it remains a great challenge to develop wearable structural hydrogels that possess simultaneously body temperature-responsive, adhesion-adaptable, and transparency-tunable. Herein, an innovative skin-mountable thermo-responsive hydrogel is fabricated, which endows tunable optical properties and switchable adhesion properties at different temperatures. Interestingly, it is able to exhibit lower critical solution temperature (LCST) to adapt to the human body temperature by altering the acrylic acid(AAc) content in the hydrogel network. The hydrogel also displays high transparency and strong adhesion at low temperatures, while it becomes opaque and feeble adhesion at high temperatures. Furthermore, a wearable and highly sensitive hydrogel sensor array structure is constructed by harnessing vat photopolymerization three-dimensional (3D) printing. As a proof of concept, a wearable hydrogel sensor attached to the back of the human hand is capable of detecting simultaneously temperature and strain differences, and also integrating high-temperature monitoring and alarm functions with visual transparency alteration. This work provides an advanced manner to fabricate structured responsive hydrogels, which have potential application prospects in the field of smart medical patches and wearable devices.