Atmospheric moisture-digesting zwitterionic skin for non-drying and self-adhesive multifunctional electronics

Hydrogel-based stretchable ionic skins have attracted extensive attention as on-skin epidermal electronics owing to their inherent biocompatibility and ionic conductivity. However, the problem that water in traditional hydrogels eventually evaporates as exposed to air largely hinders their long-term sensing applications. Herein, we report an atmospheric moisture-digesting, biocompatible, and breathable zwitterionic skin with high environmental tolerance by introducing a super hygroscopic zwitterion-glycerylphosphorylcholine (GPC) into hydrogen-bonded polyacrylic acid network. The incorporation of GPC endows the zwitterionic skin with very high water-retaining ability (~18.3 wt% water content at RH 20%) and thus superior ambient stability more than one month and freezing resistance (freezing point ≈ -74 ℃). Moreover, the multiple and reversible physical bonds in the matrix bring excellent stretchability and elastic recovery, good adhesion to various substrates, rapid self-healing, as well as moisture regeneration. The water-processable zwitterionic skin can also be used as conductive inks, utilizing its universal adhesion and adjustable rheology, to customize zwitterionic tattoos by painting or stencil printing, resulting in ultraconformal and seamless contact with irregular substrates. The zwitterionic skin with all these comprehensive advantages is demonstrated to function as a durable non-drying and self-adhesive sensing platform for multifunctional human-machine interfacing and artificial multimodal tactile sensors.