Material extrusion 3D printing with polymer microsphere inks: Effects of solid volume fraction and extrudate swell on the resolution and suitable processing parameters

Material extrusion 3D printing of semi-solid inks holds tremendous potential in the pharmaceutical industry. However, the success of the manufacturing process relies on adequate material properties and optimized process parameters. Therefore, broader adoption of the technology requires a deep understanding of the phenomena present before, during, and after the extrusion process. This paper illustrates the practical effects of extrudate swell on the 3D printing process and the resulting object quality. Extrudable inks containing polymeric microspheres embedded in a Carbopol gel matrix were studied, and the effects of extrudate swell on print quality were assessed. Neglecting extrudate swell resulted in the extension of the printed filaments, leading to shape distortion in thin-walled objects. However, extrusion rate corrections could be determined from the extrudate swell ratios, which was experimentally validated. While extrudate swell negatively affected printing resolution, a counteracting effect was also demonstrated by utilizing controlled shrinkage after printing.