3D-printable biocompatible, self-adhesive and long-term stable organohydrogel for wearable sensors

Hydrogel-based tactile sensors are promising candidates for interfacing soft biological tissues with rigid electronics due to their mechanical compliance and skin-like properties. However, challenges such as limited longterm stability and biocompatibility hinder their broader application. Here, we present a transparent, photopolymerizable, ionically conductive organohydrogel synthesized via a simple one-pot method. The formulation combines a polymerizable cationic monomer, the [2-(methacryloyloxy)ethyl]trimethyl ammonium chloride (METAC), derived from an acrylate choline chloride, with PEGDA as a crosslinker in a binary water/glycerol solvent. METAC serves dual roles as both monomer and ionic conductor, while glycerol forms hydrogen bonds with METAC, enhancing water retention and stability. The resulting material exhibits excellent stretchability (up to 225 %), linear piezoresistive behavior (GF = 1.54), and high sensitivity to low compressive pressures (3.35 kPa-1, 0-250 Pa). Moreover, long-term performance is maintained for a remarkable period of 1 year. Biocompatibility was confirmed using a 3D in vitro epidermis model, with no effect on cell viability, morphology or structural proteins. The gel is also compatible with 3D VAT photopolymerization, enabling complex, customizable geometries enhancing stress sensitivity. This versatile, stable, and skin-compatible organonohydrogel represents a promising platform for next-generation wearable sensors, soft robotics, and biomedical devices.