Dually Synergetic Network Hydrogels with Integrated Mechanical Stretchability, Thermal Responsiveness, and Electrical Conductivity for Strain Sensors and Temperature Alertors

The first example of dually synergetic network hydrogel, which has integrated mechanical stretchability, thermal responsiveness, and electrical conductivity, has been constructed by a versatile and topological co-cross-linking approach. Poly(N-isopropylacrylamide) (PNIPAAm) is introduced as the thermally responsive ingredient, and polyaniline (PANI) is selected as the electrically conductive ingredient. PNIPAAm network is cross-linked by double-bond end-capped Pluronic F127 (F127DA). PANI network is doped and cross-linked by phytic acid. These two ingredients are further mechanically interlocked. Due to the integrated multiple functionalities, the topologically co-cross-linked hydrogels, as will be mentioned as F-PNIPAAm/PANI hydrogels, can be fabricated into resistive-type strain sensors. The strain sensors can achieve a gauge factor of 3.92, a response time of 0.4 s, and a sensing stability for at least 350 cycles and can be further applied for monitoring human motions, including motion of two hands, bending of joints, and even swallowing and pulse rate. Moreover, F-PNIPAAm/PANI hydrogels are utilized to construct efficient temperature alertors based on the disconnection of circuits induced by volume shrinkage at high temperature.