Advective Assembly Extrusion and its Bioprinting Applications with Gelatin Methacryloyl and Polyacrylic Acid

• Clara Middleton, Chemistry, Davidson College

• Alexandra Bayles, Chemical and Biomolecular Engineering, University of Delaware

3D printing makes personalizing health care possible. It can be cheaper, faster, and more precise than traditional fabrication methods. Bio-printing, which uses cell-laden materials in 3D printing, has many applications such as tissue implantation, pharmaceutical testing, and cancer studies. In traditional extrusion-based bioprinting, patterning fine features that are relevant to biological systems requires using small diameter nozzles. As a consequence, print speeds must be slowed drastically to prevent cell death from shear stresses during printing. This problem can be addressed with an advective assembly (AA) nozzle, which pre-assembles patterns before reaching the print bed using laminar flow operations that split, rotate, and recombine two different inks. Because of this pre-patterning, microscale patterns can be achieved without reducing the overall nozzle diameter, thereby preventing cell death without compromising print speed. Here, extruded filaments with two bioinks are patterned using AA nozzles: a gelatin methacryloyl (GelMa)-based microgel is used as a cell-laden ink, and polyacrylic acid is used as a cell-free ink to direct cell placement and growth. To design printable inks, we looked at their rheological properties including yield stress, shear thinning, and recoverability. We found that the GelMa microgel cures and appears to be printable, though it needs more fine-tuning, because its composition is heat sensitive, which is not ideal when printing cells that require higher temperatures after printing.