Optimization of the Rheological Properties of Fumed-Silica-Based Supporting Baths for Embedded Printing and Reduction of the Effect of Crevasse Formation

In embedded 3D printing, the supporting gel must provide the right rheological properties to keep the ink in place. It has previously been shown that a strong and stable 3D network can be formed by particle–particle interactions of hydrophobic fumed silicas suspended in a polar solvent. Here, the rheological properties of fumed silica gels in polyethylene glycol (PEG) are investigated. The recovery properties like storage modulus, yield stress, and recovery time of the gels made of fumed silica with alkyl-chains of different lengths are studied. A very fast recovery time (0.2 s) is achieved by increasing the length of the alkyl chains on the silica surface, leading to embedded printing results with high shape accuracy. However, with the engineered supporting gel, the formation of crevasses affects the shape of the filament. Previous approaches to reduce crevasse formation include the introduction of liquid fillers to avoid such distortions, which, however, prevents the reuse of the gels and leads to increasing waste production in embedded printing. Here, it is shown that by adjusting the rheology of the inks to fit the rheology of the supporting gel, high-shape accuracy prints with ideally round-shaped filaments can be achieved without the need for liquid fillers.