Embedded 3D printing is a growing fabrication technique wherein a nozzle is submerged into a viscoelastic support bath and extrudes continuous filaments (embedded ink writing) or droplets (embedded droplet printing). The support bath holds the shape of the printing part. As such, embedded 3D printing allows for greater flexibility in ink rheology than conventional direct ink writing, making this technique advantageous for bioprinting, since inks can be designed for biocombatilibity instead of printability. However, certain combinations of ink and support materials can produce surface roughness on individual filaments, which can compromise part integrity. Using computational fluid mechanics simulations in OpenFOAM and in-situ imaging experiments in model materials, we find that filament surface roughness is controlled by the support Capillary number and the ratio of the ink Reynolds number to the support Reynolds number. As such, the interfacial tension, the viscosity ratio, and the translation speed to flow speed ratio are critical tools for controlling roughness. This talk addresses a key question in the embedded 3D printing literature: whether the ink-support combination should have a high or low interfacial tension. We find that a non-zero surface tension can be a powerful tool for suppressing roughness, but appropriate viscosities and print speeds must be chosen to suppress filament instabilities which emerge at non-zero surface tensions, including filament rupture and buckling.

Controlling filament roughness in embedded 3D printing of soft materials

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.