Direct-ink-write 3D printing of highly-stretchable polyaniline gel with hierarchical conducting network for customized wearable strain sensors

The development of direct-ink-write (DIW) 3D printing conducting polymer gels with remarkable mechanical properties, satisfactory conductivity, and customized three-dimensional structures is in high demand for next-generation wearable strain sensors, yet challenging due to the difficulty of preparing conducting polymer solutions with high concentrations. Herein, a novel cellulose nanocrystal (CNC)-regulated polyaniline (PANI) composite ink for DIW 3D printing customized wearable strain sensors with high stretchability and hierarchical conducting networks is fabricated. With the employment of CNC as a stabilizer to regulate the intermolecular interactions, the in-situ polymerized composite ink achieves well-dispersed PANI and abundant reversible intermolecular interactions, which is favorable for DIW 3D printing PANI composite gel with tailored planar patterns of high geometric accuracy. Benefiting from the hierarchical gel frameworks and abundant non-covalent interactions within the PANI-based composite ink, the PANI composite gel exhibits remarkable stretchability, promising low-temperature tolerance and excellent strain sensing performance. Due to its unique wavy mesh structure, the DIW-printed PANI composite gel-based wearable strain sensor is more sensitive and can accurately detect changes in the human body. This work aims to expedite the advancement of DIW printing conducting polymer gel for the development of personalized wearable strain sensors and advanced flexible electronics.