Versatile Hydrogel Based on a Controlled Microphase-Separation Strategy for Both Liquid- and Solid-Phase 3D Printing.

Hydrogels are considered indispensable materials for fabricating flexible devices with their excellent flexibility and workability. To efficiently transform hydrogels into flexible devices, three-dimensional printing technology offers a powerful approach. However, hydrogels suitable for a single printing strategy have proven inadequate for fabricating flexible integrated devices. Herein, we report a simple and two-phase 3D-printed hydrogel (TP-3DPgel) achieved through a controlled microphase-separation strategy. The microphase-separation regions can undergo reversible changes through pH adjustment, giving TP-3DPgel an extremely broad viscosity tuning range from liquid to solid states. This overcomes limitations imposed by extreme rheological properties in different 3D printing processes, making this ink suitable for both liquid-phase digital light processing (DLP) 3D printing and solid-phase direct ink writing (DIW) 3D printing. Simultaneously, the TP-3DPgel exhibits excellent mechanical properties, including high stretchability (>1100%), high strength (0.82 MPa), low hysteresis (∼5.4%), and fatigue resistance. Moreover, TP-3DPgel exhibits high-resolution 3D printing capabilities, making it suitable for both DLP and DIW-3D printing to achieve high-quality fabrication from 2D filaments to 3D structures. Interestingly, we utilized both DIW and DLP-3D printing to fabricate various functional flexible devices, including energy storage devices, sensors, and electronic skins, showing in detail the outstanding compatibility and processability of TP-3DPgel, which offered a reliable strategy for 3D printing functional devices.