High Precision Embedded 3D Printing of Soft Materials via the Solvent Exchange Method

Embedded 3D printing enables the direct ink writing of ultrasoft materials which, due to gravity, cannot support their own weight in the air such as large aspect ratio 3D objects, thin closed shells, and hierarchically branched vessel networks. The support gel surrounding the extruded filaments prevents their sag or collapse. Gel-embedded printing resolution is currently on the order of 50 micrometers, limited by the interfacial tension ratios of the printing materials and support gel, the viscosity and the yield stress of the two materials, and the time required to post-cure by heat or UV light. Herein, we have significantly extended the library of printable materials and the achievable resolution and feature size by developing an embedded ink write exploiting the solvent exchange method. The printed material is initially dissolved in a solvent, which as soon as the filament is extruded from the nozzle solidifies due to the miscibility of the solvent in the gel. Hence, no post-curing is required, and the resolution is only limited by the nozzle size down to 3.2 micrometers. We applied this method to print intricate thread spools mimicking the skeins found in the hagfish slime, hair arrays, and complex fiber architecture similar to those found in biological tissue.