Abstract

Flexible sensor applications have increasingly focused on ionically conductive hydrogels due to their notable deformability and easily tunable properties compared to rigid materials. These hydrogels are conductive thanks to their high water content and porous structure, enabling effective ion transfer. Despite their attractive features, hydrogels have limited water retention and shape fidelity, and they are more typically inspected as two-dimensional films and patches. Here, 3D printed thermoplastic polyurethane (TPU) frames with various geometries were injected with ionic conductive hydrogels to create durable, robust soft mechanical sensors for detecting mechanical stimuli through changes in their electrical resistance. After the TPU encasement was shown to maintain the hydrogel water content, hydrogel-embedded frames with varying geometries were designed. Their response to mechanical loading was investigated in relation to their dimensions and geometric shape. Finally, glove-shaped frames were fabricated and injected with ionic hydrogel for sensing abilities. The wearable sensors accommodated free movement of the fingers in multiple directions and were able to detect simultaneous and independent bending and stretching of the fingers. Through comprehensive observation of the electrical behavior of the ionic sensors in response to different kinds of mechanical stimuli, it was concluded that the resistance change following mechanical loading was dependent on the geometric features of each hybrid sensor. Thus, hydrogel-embedded TPU encasement could be designed with targeted geometry to dictate the type and direction of mechanical sensing. This work presents a facile approach to fabricating multi-component soft geometric sensors with potential to be used for wearable electronics and human-machine interactions.