Numerical study on the influence of process parameters in direct ink writing of high viscosity bio-inks

This study uses a computational fluid dynamics model to investigate the effect of direct ink writing process parameters on the quality of 3D-printed sedimentary materials. The numerical simulation employs the level-set method of the two-phase flow module of COMSOL Multiphysics software. The selected bio-ink consists of the powder portion (45s5 bio-glass and beta-TCP nanoparticles) and the polymer portion (polyvinyl alcohol), which has applications in constructing biological bone scaffolds. First, the empirical results validate the extrudate shape obtained from numerical simulation. According to the observations, increasing the inlet velocity from 15 mm/s increased the extruded ink distortion, and finally, at 50 mm/s, the distortion reached its maximum. Secondly, after calibration and validation results, the role of the most common nozzles with different diameters and input speeds on the maximum ink output velocity of the nozzle is predicted. Finally, the influence of the two dimensionless parameters (the ratio of the distance between nozzle and bed to nozzle diameter and the ratio of inlet ink velocity to print speed) on the adhesion and shape of the printed layers is examined. At distances greater than 1.5 times the diameter of the nozzle, when the extrusion speed is greater (more than 1.5 times) relative to the linear speed of the nozzle, the printed filament becomes uneven. Reducing the speed ratio between 1x and 1.5x prevents the printed filament from sticking to the substrate or causing distortion.