Impact of cell density on the bioprinting of gelatin methacrylate (GelMA) bioinks

3D printing of cell laden bioinks has the potential to recapitulate the hierarchical and spatial complexity of native tissues. However, the addition of cells can alter physical properties of printable resins, which in turn may impede or induce cellular sedimentation or affect the printability and shape fidelity of the final construct. In this study we investigated these considerations by bioprinting gelatin methacrylate (GelMA) bioinks, loaded with various concentrations of mouse fibroblast cells (L929), using extrusion-based direct-write 3D printing (EDP). The impact of various cellular concentrations on viscosity, and temperature-driven gelation of GelMA was examined with a rheometer. The effect of cell concentration on quality of 3D printed GelMA hydrogels was investigated by analyzing the geometric compliance of the 3D printed scaffolds to the theoretical model, and by studying compressive properties of the 3D printed scaffolds. The addition of cells did not significantly affect GelMA zero-shear viscosity or viscosity at shear rates associated with EDP (>102 s−1). While quality and resolution of cell-laden 3D scaffolds of GelMA hydrogel were slightly better than that of GelMA hydrogels without cells, there were no significant differences due to various cell concentrations. The cellular sedimentation in GelMA bio-inks within the printer cartridge was evaluated using DNA quantification. Sedimentation was not statistically significant at the studied cell concentrations of up to 10 ​× ​106 ​cells/ml. Immunofluorescent imaging indicated improved cell spreading and more uniform scaffold coverage over time for higher cell densities. This study provides insights into the effect of cell density on the rheology, and 3D printability of GelMA bioinks which will assist in the designing and standardizing bioprinting of high-quality 3D bioengineered structures.