Orthogonal Growth for Fabricating Hydrogel Sensors and Circuit Boards with In Situ Post-Tunable Performance

Conductive hydrogels generally possess dual network structures consisting of hydrophilic cross-linked polymer frameworks and conductive paths. The post-modification of their structures and performance for fabricating devices with 3D conductive patterns is challenging because of their covalently cross-linked complex matrices. Here, an orthogonal-growth strategy is described for modulating all-aspects of conductive hydrogels, including size, pattern, conductivity, and conductive path. In this strategy, the matrices controlling samples' size and the functional components modulating samples' conductivity can be orthogonally varied by feeding corresponding nutrients. Using poly(hydroxyethyl acrylate)-polyaniline organohydrogels (PHEA-PANI) as an example, it is demonstrated that the samples can incorporate the hydroxyethyl acrylate monomer to expand (21.9-fold in weight is shown) or integrate aniline into the conductive networks to tune conductivity (from 0 to 42.6 mS cm(-1)) without changing the sample size. Moreover, the growth of PANI is spatially selective. Exploiting the selective modulation of various parameters through this method, strain sensors with post-modulated sensing performance and 3D hydrogel circuit boards are fabricated.