Reversible and dynamic thermoregulatory energy-free electronic skin for the homeostasis via thermo-responsive hydrogel

Abstract

Temperature is one of the most valuable sensations that come from a mechanoreceptor of our skin. Communication, exercise, and even sleeping from morning till night need a considerably optimized temperature to feel stability, smoothness, and satisfaction in daily lives. In a living organism, there should be specific and comfortable temperature ranges for individuals. However, the heat from the body and constituents interchange with various energies surrounded the environmental system for a flash moment and continuous state. The importance of homeostasis is the maintenance of qualified conditions that organs, muscles, and even the atomic unit of cells could activate in an adequate state for their purpose, respectively. To accomplish homeostasis, a skin should block the body heat from conduction, convection, and thermal radiation from the inner layer to the outer surface in a cold state. The heat release is crucial not to be heated until some human body goes through severe injuries when the body temperature is too high. Effective heat management systems have been developed to cool down and heat up to achieve each purpose of devices. Micro-engineering, metal deposition, joule heating, and thermoelectric methods are applied to diverse substrates and devices. The Heating devices based on microstructure show the outstanding capability of blocking thermal radiation by micro-pores of engineered textiles and fabrics. Moreover, metallic particles have been utilized to improve device performance by reflecting every range of radiation. Although the improved heating effect influences higher temperature increasement, pore-based structure and metal combination are vulnerable to strain stress and easy to be delaminated. On the other hand, the cooling devices based on aligned 2D materials such as BN (boron nitride) successfully control the direction of 2D materials for certain direction simultaneously, and based on thermoelectric devices present switching mode to regulate both hot and cold mode for matching temperature of virtual reality systems on the surface of which applicant wear. Nevertheless, the fabrication process and complex routing systems with burdensome energy support circuits to utilize thermoregulate systems make it difficult to be applied to various types of circumstances and daily lives. Herein, we envision the reversible and dynamic dual-mode electronic skin for homeostasis, optimizing biocompatible hydrogels, conducting polymers, and Omni-axial stretchable patterns. As thermo-responsive hydrogel N-isopropylacrylamide (NIPAM) has a shrunken nature when a temperature is over LCST (lower critical solution temperature), heat preservation occurs because of reflecting thermal radiation dominated by propyl group, which expels hydrogen atoms out of the hydrogel network. Contrary to the under LCST, heat release mode becomes, accommodating hydrogen atoms inside the hydrogel network dominated by an amide group. Kirigami pattern combined with conducting polymer and Ag nanowires in the PNIPAM hydrogel layer makes it possible to regulate temperature depending on the temperature states. This new type of thermoregulatory electronic skin might be a new possibility to solve the critical problem, which is not in the spotlight.