Multi-responsive 3D printable organohydrogel for the fabrication of durable and low-hysteresis flexible sensors

Ionically conductive hydrogels have emerged as promising candidates for sensors in wearables and prosthetics due to their high flexibility and stretchability. However, those suffers intrinsically of a strong limitation which is water evaporation, that over time alters their mechanical and electrical properties, restricting their usage. On the other hand, the use of organohydrogels limits this drawback, controlling rate of evaporation and thus preserving the device properties. This study introduces a double-network, conductive, 3D-printable hydrogel where water is partially replaced by glycerol using a solvent replacement strategy to prevent evaporation and preserve electrical and sensing properties. This organohydrogel exhibits excellent stretchability (up to 350 %), high strain and pressure sensitivity, and negligible hysteresis. Moreover, the mechanical and electrical characteristics of the organohydrogel remain stable for more than six months. The sensor demonstrates an outstanding strain detection limit of 0.05 % and a pressure detection limit of 1.5 Pa, enabling the evaluation of micrometric deformations across a wide temperature range, including below room temperature. The use of glycerol, a high boiling point and biocompatible solvent, allows both temperature and humidity sensing, enhancing the versatility of this organohydrogel. Since the solvent replacement strategy is applied to the already formed hydrogel, its 3D printability remains unaffected, enabling the enhancement of sensing properties through complex 3D structuring. The excellent time stability of mechanical and sensing properties, combined with sensitivity to both micro and macro deformations, temperature and humidity responsiveness, highlights the potential of this organohydrogel in a broad spectrum of flexible sensing applications.