Modulation of conductive hydrogel structures via direct ink writing and freezing–thawing

Soft electronic sensors based on conductive polymer hydrogels have been increasingly studied toward such applications as healthcare, human–machine interactions, and soft robotics. Correspondingly, the pursuit of high sensing performance often involves the regulation of multifaceted structural and functional properties of the hydrogels. Among various hydrogel types, poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) and poly(vinyl alcohol) (PVA) hybrid structures obtained via the 3D printing technology and the freezing–thawing method have exhibited notable potential for developing soft, high-performance electronic sensors. However, the tuning of micromorphological and functional characteristics of PEDOT:PSS/PVA structures via such approaches for electronic sensing performance has yet to be further explored. Here we show a strategy for modulating the multifaceted characteristics of PEDOT:PSS/PVA hydrogel structures via the combination of direct ink writing and freezing–thawing. The influence of material composition ratio on different properties of PEDOT:PSS/PVA hydrogel was examined. The internal microscale morphologies and the mechanical properties of PEDOT:PSS/PVA hydrogels prepared by freezing–thawing cycles at different freezing temperatures were characterized to reveal the correlation. Subsequently, direct ink writing followed by freezing–thawing was employed to generate PEDOT:PSS/PVA hydrogel structures with tunable characteristics. Eventually, electrophysiological sensing capability of PEDOT:PSS/PVA hydrogel structures obtained with the proposed fabrication method was demonstrated. The findings in this study may be utilized to generate conductive polymer hydrogel structures with specific properties for different sensing applications.