Abstract

Field-assisted 3D printing has promising applications including cell patterning and functionally graded scaffolds. Direct ink writing can produce 3D-printed multiphase materials with controlled phase distributions established by external fields (such as acoustic fields), which manipulate the position and orientation of particles within the print nozzle. After the filament exits the nozzle, its internal microstructure changes because of deposition, relaxation, and shear during writing of the neighboring lines. Using particle image velocimetry and digital image analysis, we track changes in the internal structure of the deposited filaments during direct ink writing into a yield stress fluid support material, which enables deposition of low-to-moderate viscosity inks. Transverse fluid flows across the filament and particle distribution positions and widths are governed by viscoplastic support flow, unsteady disturbed zone flow, capillarity-driven spreading, and gravity-driven spreading. Plastic flow and disturbed zone flow act on shorter timescales and influence microstructural changes during deposition and shear, while spreading acts on longer timescales and influences changes during relaxation. However, these four effects interact. Changes during deposition and relaxation, and shear correlate with each other. As such, there is often a trade-off between accurate particle positioning and precise particle packing. Understanding the complexity of these interactions can guide development of in situ curing to preserve particle distributions in their optimal state.