Embedded 3D Printing with Acoustic Focusing

Intra-nozzle particle positioning methods enable the design of composite 3D printed components with structural and functional gradients. One method is acoustic focusing, wherein a piezoelectric actuator establishes a bulk acoustic wave in the nozzle which co-orients and moves particles to the wave nodes. Because acoustic focusing requires low viscosity inks (such as soft materials with functional particles), we use a granular hydrogel as support material. This study investigates how layer-by-layer deposition of support material and printing into a support bath each influence the maintenance of acoustically focused microstructures and the fidelity of printed structures. While layer-by-layer support prevents filaments from breaking into droplets, it can also destabilize filaments near liquid elbows and induce rotational flows that disrupt focused structures. Similarly, though writing into support material enables complex structures, it can also hinder inter-layer and intra-layer fusion and disrupt existing structures. Using digital image analysis and particle image velocimetry, we measure the effects of ink and support composition and printing parameters on maintenance of acoustically focused microstructures, stability of filaments and liquid elbows, and inter-filament fusion.