Design of low temperature-responsive hydrogels used as a temperature indicator

Development of highly thermo-sensitive hydrogels, particularly at a low-temperature range, has promising applications in diverse fields. Herein we designed, synthesized, and characterized tri-copolymer poly(N-tert-butyl acrylamide-co-N-isopropyl acrylamide-co-acrylamide) p(NTBAM-co-NIPAM-co-AM) hydrogels using a facile one-pot method. The copolymerization of two thermo-responsive monomers of NTBAM and NIPAM with hydrophilic AM monomers aimed to tune the temperature range of lower critical solution temperature (LCST) between 8 degrees C and 10 degrees C by varying the concentrations and molar ratios of NTBAM, NIPAM, and AM. At optimal conditions, p (NTBAM-co-NIPAM-co-AM) hydrogels showed a rapid and large deswelling by reducing their original sizes by 21% in 2 min as temperature was slightly changed from 8 degrees C to 10 degrees C. Such low-temperature-triggered deswelling behavior and tunable LCST property are likely attributed to delicate interplay between different network components and their interactions with water. Due to high temperature sensitivity (similar to 2 degrees C), large volume deswelling ratio (90%), and low temperature-responsive range (8-10 degrees C), we further demonstrated a prototype hydrogel ball actuator as temperature indicator to monitor minor temperature-induced size changes. The design strategy for this p(NTBAM-co-NIPAM-co-AM) hydrogel could be generally applicable to other thermo-responsive hydrogels with different shapes and temperature-responsive ranges, which could be used as low-temperature indicator for many applications including vaccine storage and transportation.