Photocuring 3D printable flexible strain sensor enhanced by in situ grown silk fibroin nanoparticles

The growing demand for flexible strain sensors across diverse applications necessitates elevated standards regarding the outstanding mechanical performance and customizability of their polymer-based substrates. In this study, the ionically conductive gels with in situ generation of silk fibroin nanoparticles (SFN) for photocuring 3D printing were successfully designed. The silk fibroin underwent chain folding as a result of phase separation with the photocurable resins (PCR), leading to the direct in situ generation of nanoparticles within the PCR. The results demonstrated a significant improvement in the stability of liquid PCR/SFN and the mechanical performance of ionogels prepared via the in situ SFN growth method, manifesting a notable enhancement in tensile strength and elongation at break by 340% and 62.8%, respectively. Moreover, reliable loading behavior was maintained under large strain conditions of 600% tensile strain and 50% compressive strain throughout long-term cycles, accompanied by stable signals. The customization, stability, and sensitivity of sensing behavior were achieved through the fabrication of customized porous-structured flexible sensor components from the PCR/SFN system, including a series of finger, wrist, and throat sensors, as well as an insole gait sensor. The facile strategy of in situ SFN growth could be an effective approach for manufacturing nanocomposite conductive ionogels, offering new avenues for modulating the mechanical performance of 3D-printed flexible strain sensors.