Rheological design of colloidal suspension for direct 3D ink writing

Direct ink writing of functional materials requires colloidal suspensions that can flow smoothly through a nozzle while rapidly solidifying after deposition to retain the printed geometry. In this study, we present a general strategy for designing particle-based inks by jointly controlling their rheological behavior and post-extrusion solidification. The particle volume fraction was systematically adjusted to regulate interparticle interactions, viscosity, yield stress, and shear-thinning behavior. In parallel, the particle surface chemistry was engineered to control colloidal stability, particle-to-particle linking reaction, and the formation of a mechanically robust network after printing. These approaches enabled the preparation of functional-material suspensions that exhibited efficient extrusion under shear and rapid structural recovery or solidification following deposition. By balancing ink flowability, filament stability, and interlayer adhesion, three-dimensional architectures with controlled geometries were fabricated through direct ink writing. Further optimization of particle interactions and solidification kinetics enabled fine-feature printing and microscale patterning. This work demonstrates that solidification design, combined with conventional rheological engineering, provides a versatile framework for the additive manufacturing of diverse particle-based functional materials across multiple length scales.