DLP 3D printing of electrically conductive hybrid hydrogels via polymerization-induced phase separation and subsequent in situ assembly of polypyrrole

Abstract

Functional conductive hydrogels are widely used in various application scenarios, such as wearable sensors, tissue engineering scaffolds, and biosensing devices. Simultaneously achieving good conductivity and shaping versatility is still a great challenge. In this work, an inherently porous poly(N-isopropylacrylamide) (PolyNIPAm) hydrogel was constructed utilizing the principle of polymer-induced phase separation. The instantaneous heat release during the UV-initiated polymerization reaction increased the temperature of the system above the lower critical solution temperature (LCST), triggering the phase transition of the PolyNIPAm chains. Subsequently, an interconnected polypyrrole (PPy) network within the hydrogel was obtained through in situ catalytic pyrrole polymerization. The resulting hybrid hydrogel demonstrates an exceptional electrical conductivity of 264 S m⁻¹. Moreover, this method shows good compatibility with digital light processing (DLP) 3D printing technology, enabling the conductive hydrogel to acquire tailored complex features. The conductive hydrogel is 3D printed into a lattice-like structure and used as a piezoresistive sensor. Benefiting from its 3D structure, it can maintain high sensitivity over a wide range of detectable pressures. With this remarkable advantage, this fabrication strategy may provide new opportunities to broaden the applications of conductive hydrogels.