3D-Printed Wearable Strain Sensors Utilizing Deep Eutectic Solvents and Fumed Silica Nanoparticles.

Dry ionic elastomers based on polymerizable deep eutectic monomers (DEMs) have attracted increasing attention for flexible strain-sensing applications; however, their direct fabrication from printable ink formulations into functional sensors remains limited. In this study, we developed a printable gel system by incorporating fumed silica nanoparticles into a DEM composed of choline chloride and acrylic acid. The well-dispersed mixture formed a shear-thinning sol that transitioned into a physically cross-linked gel above a critical silica concentration, exhibiting rheological properties suitable for direct ink writing. Notably, no chemical cross-linker was added to the formulation. Upon UV curing in the presence of a photoinitiator, acrylic acid was polymerized within the physically structured gel, converting the printed ink into a DEM-derived dry ionic elastomer with tunable mechanical and electrical properties. The cured structures were transparent, flexible, and conductive, showing strong potential for use in strain-responsive applications. The printed sensors generated consistent electrical signals under deformation, supporting their applicability in wearable electronics and motion monitoring platforms.