2, Mechanical Engineering, University of Massachusetts Lowell, Lowell, Massachusetts, United States
Since the emergence of the technology, 3D bioprinting has been applied to many areas of biomedicine such as creating customized devices, flexible bioelectronics, and scaffolds for tissue regeneration, novel therapeutic systems, prosthetics, and orthodontics. The macro-architecture of the generated construct can be as complex as the anatomical feature of the desired tissue, which necessitates proper printing fidelity. Printing resolution depends on the technical specifications of bioprinters and the physical properties of bioinks. In this work, a numerical model based on the method of volume of fluid (VOF) was created to obtain some insights on the droplet generation in inkjet bioprinting. Our simulations revealed the spatial and temporal features of the droplets before they impact the substrate, which is highly difficult to observe through experiments. The results further showed that high hydrophobicity of the substrate yielded a better printing resolution and lower stability for bioprinting. We then simulated the process of deposition from a sub-millimeter sized nozzle in extrusion bioprinting. In contrast to inkjet printing, the viscosity was found to be a dominant factor for flow properties inside the nozzle and after deposition. The viscosity dependency of shear rates also affects the surface deformation of the bioink when it leaves the nozzle and the combination of flow-induced stresses with surface tension forces dictates the form of the spherical residue formation. Based on our simulations, by selecting proper bioink properties, the resolution can be improved significantly in extrusion and inkjet bioprinting techniques.