3D Printing Soft Silicones: Additive Manufacturing at Ultra-low Interfacial Tension

Soft silicone structures are difficult to fabricate using the conventional FDM approach to 3D printing. Without adding rheological modifiers to silicone inks, printed features will sag and spread upon deposition from the nozzle. Embedded printing into jammed support materials helps to overcome this challenge by trapping the silicone ink in space as it is printed, eliminating the need for modifying the ink formulation with additives. However, previously developed support materials for 3D silicone printing exhibit a large interfacial tension against silicone inks, creating instabilities that deform and break up fine features, setting a minimum stable feature size. These instabilities can be prevented by developing a jammed support material that is chemically similar to silicone oil and, consequently, has ultra-low interfacial tension against silicone inks. Such a material would enable 3D printing of accurate and high-resolution structures having fine feature sizes. In the work presented here, we developed a silicone oil-based support material having tunable rheological properties that can be optimized for embedded 3D printing of soft silicone. We show that by practically eliminating interfacial tension between silicone ink and the silicone-based support material, features as small as 8 microns in diameter can fabricated; these fine features are indefinitely stable over time. Using this new material, we are able to fabricate robust, accurate, and complex structures like a model brain aneurysm for surgical simulation and a functional tri-leaflet heart valve model for potential biomedical applications.