Computational fluid dynamics for the optimization of internal bioprinting parameters and mixing conditions

Tissue engineering requires the fabrication of three-dimensional (3D) multimaterial structures in complex geometries mimicking the hierarchical structure of biological tissues. To increase the mechanical and biological integrity of the tissue engineered structures, continuous printing of multiple materials through a printing head consisting of a single nozzle is crucial. In this work, numerical analysis was carried out to investigate the extrusion process of two different shear-thinning biomaterial solutions (alginate and gelatin) inside a novel single-nozzle dispensing system consisting of cartridges and a static mixer for varying input pressures, needle geometries, and outlet diameters. Systematic analysis of the dispensing process was conducted to describe the flow rate, velocity field, pressure drop, and shear stress distribution throughout the printing head. The spatial distribution of the biopolymer solutions along the mixing chamber was quantitatively analyzed and the simulation results were validated by comparing the pressure drop values with empirical correlations. The simulation results showed that the proposed dispensing system enables to fabricate homogenous material distribution across the nozzle outlet. The predicted shear stress along the proposed printing head model is lower than the critical shear values which correspond to negligible cell damage, suggesting that the proposed dispensing system can be used to print cell-laden tissue engineering constructs.