Materials with controlled porosity have found diverse applications in separation, catalysis, energy storage, sensors and actuators, tissue engineering, and drug delivery. Multiple methods have been developed to fabricate well-defined porous materials with the pore sizes ranging from nanometers to millimeters. The introduction of sacrificial templates, for example, can impart porosity to the materials, encapsulating them after the removal of embedded materials. Alternatively, procedures involving phase separation, direct templating, and chemical reaction have demonstrated fabrication of hierarchical porous structures. These methods inherently require multiple steps and are limited in the attainable complexity of the fabricated structures.
Recent advances in digital fabrication, represented by 3D printing, have enabled fabrication of porous 3D structures consisting of polymeric materials with porosity, yet are limited by materials applicable to the process. Solvent-casting 3D printing (SC3DP) — direct 3D printing of polymer inks with in-situ evaporation of solvents — has allowed fabrication of 3D porous structures with the stringent requirement of rheological properties of the printing ink (e.g. high viscosity and high vapor pressure).
Researchers have developed a novel 3D printing method — called immersion precipitation 3D printing (ip3DP) — to fabricate 3D porous models in one step. In this approach, inks containing polymers were directly printed in a bath of a non-solvent and the printed ink solidified rapidly via immersion precipitation. Spontaneous solidification via immersion precipitation generated porosity at micro-to-nano scales.
The porosity of the 3D-printed objects is easily controlled by the concentrations of polymers and additives, and the types of solvents. A wider selection of solvents permitted a wider range of thermoplastics to be printed. To highlight this capability, fabrication of centimeter-scale models in 13 polymers dissolved in six solvents was demonstrated.
This work demonstrates three-dimensionally controlled immersion precipitation based on digitally controlled depositions of materials. The wide selection of printable materials and the ability to tailor their morphologies and properties makes ip3DP a novel approach for 3D printing to fabricate functional structures.