Phase-Change-Enabled, Rapid, High-Resolution Direct Ink Writing of Soft Silicone.

Soft silicone is an ideal flexible material for application, e.g., in soft robotics, flexible electronics, bionics, or implantable biomedical devices. However, gravity-driven sagging, filament stretching, and deformation can cause inevitable defects during rapid manufacturing, making it hard to obtain complex, high-resolution 3D silicone structures with direct ink writing (DIW) technology. Here, rapid DIW of soft silicone enabled by a phase-change-induced, reversible change of the ink's hierarchical microstructure is presented. During printing, the silicone-based ink, containing silica nanoparticles and wax microparticles, is extruded from a heated nozzle into a cold environment under controlled stress. The wax phase change (solid-liquid-solid) during printing rapidly destroys and rebuilds the particle networks, realizing fast control of the ink flow behavior and printability. This high-operating-temperature DIW method is fast (maximum speed ≈3100 mm min ) and extends the DIW scale range of soft silicone. The extruded filaments have small diameters (50 ± 5 µm), and allow for large spans (≈13-fold filament diameter) and high aspect ratios (≈1), setting a new benchmark in the DIW of soft silicone. Printed silicone structures exhibit excellent performance as flexible sensors, superhydrophobic surfaces, and shape-memory bionic devices, illustrating the potential of the new 3D printing strategy.