Artificial Sweat Glands Based on Nanoclays and Thermoresponsive Hydrogels

Abstract

Energy-saving materials have been attracting significant interest in human society. Thermoresponsive hydrogels are capable of cooling hot surfaces by the controlled evaporation of water, which could function in any case as long as there is a constant supply of water, such as in case of rains. However, smart responsive cooling materials mimicking sweat glands in nature have never been developed because of the lack of a mechanism for the prevention of water evaporation under cool conditions. Herein, we developed an artificial material mimicking sweat glands based on the surface micro-cracking mechanism, which was composed of a thin layer of nanoclays (NC) stacked on the top surface of a poly(N-isopropylacrylamide) (PNIPAm) hydrogel mimicking the layered structures of corneocytes; the NC layer acted as a responsive barrier. At hot temperatures above the lower critical solution temperature (LCST) of PNIPAm, the surface layer underwent micro-cracking, offering rapid pathways for the evaporation of water, similar to the ducts of sweat glands. A temperature decrease of 15-30 degrees C was successfully achieved at hot temperatures, while the evaporation of water at cool temperatures below the LCST was effectively limited by the NC layer. This novel responsive gating mechanism based on the surface micro-cracking of a thin NC layer could pave a route for the future development of intelligent artificial sweat gland systems for controlled cooling and transport.