Nanochitin and poly(N-isopropylacrylamide) interpenetrating network hydrogels for temperature sensor applications

A strengthened interpenetrating network of 2,2,6,6-tetramethyl-piperidine-1-oxyl (TEMPO)-oxidized nanochitin (TOChN) with poly(N-isopropylacrylamide) (PNIPAm) chains was constructed in an acetic acid coagulation bath to fabricate hydrogels. The TOChN increased the water retention of the PNIPAm hydrogels while maintaining the lower critical solution temperature (LCST) at approximately 34 °C. The storage modulus and compression stress of the 0.62% TOChN@PNIPAm hydrogel were increased by about 32 and 13.47 times, respectively, compared among those as the pure PNIPAm hydrogel. These effects were accompanied by the transformation of the dominant network structure from PNIPAm molecular chain interactions to TOChN nanofibrillar cross-linking. In addition, TOChN@PNIPAm showed a shrinking-reswelling ability with a reserved shape. Fe³⁺ was further introduced to chelate with carboxyl groups on TOChN, which not only substantially increased the mechanical properties but additionally provided good conductivity for the hydrogels. Therefore, a temperature sensor was designed and showed a good thermal-resistance response, providing potential biosensor applications.