Parameter optimization for 3D bioprinting of hydrogels

Successful bioprinting of hydrogels relies on geometric accuracy and cell viability, both of which are influenced by a number of variable printing parameters. Despite much research aimed at the resulting quality of bioprinted structures, there is no standard method of comparing bioprint results. In this study, we have developed a simple method of assessing the bioprint results from a range of printing parameters in a standardized manner applicable to extrusion-based bioinks. The purpose of the parameter optimization index (POI) is to minimize the shear stress acting on the bioink, and thus on the encapsulated cells, while ensuring the maximum geometric accuracy is obtained. Here we demonstrate the use of the POI on a blend of 7% alginate and 8% gelatin, and test the printing achieved through 25, 27, and 30 gauge print nozzles at 1-6 mm/s print speeds, and at 100-250 kPa print pressures. In total, we tested 72 printing configurations. Our data shows that for this particular hydrogel blend, the optimum print is obtained with a 30 gauge nozzle, 100 kPa print pressure and 4 mm/s print speed. The POI is intuitive and easy to assess, and could be a useful method across a wide range of 3D bioprinting research and development applications.