Numerical modeling of inkjet cell output under the interplay of cell-laden bioink consumption and sedimentation

Inkjet printing utilizes the bioink involving biological materials and living cells to generate cell-laden droplets for precise construction of 3D tissue/organ models in a layer-by-layer manner. While printing, the suspended cells in bioink sediment due to predominant gravitational force, and form cell aggregates. It is increasingly difficult to transfer aggregates to the nozzle dispenser, resulting in gradual decay of the cell output, which becomes a critical challenge significantly affecting printing reliability and quality. This study has proposed a computational model coupling the cell flow field due to cell sedimentation and the bioink flow field due to bioink consumption. The modeled cell output has been validated by the experimental results showing a good agreement. Precise prediction of cell output enables optimization of the bioprinting process with less trial-and-error cost and promotes fabrication of more consistent and reproducible bioconstructs. The study finds that (1) the measured cell sedimentation velocity at bioink reservoir bottom increases due to the greater cell aggregates formed while printing; (2) the cell movement dynamics revealed by the model exhibit reduced movement from the sides towards the center of the bioink reservoir due to an increased sedimentation effect over printing; (3) the cell output decreases by 75 % within 60-minute printing at 400 Hz frequency. Applying greater inkjet frequency from 200 to 1000 Hz enables greater cell output efficiency from 0.48 to 0.93; (4) under 75 % preset efficiency criterion, applying frequency > 97 Hz for 60-minute printing is recommended to secure positive cell output considering the minimal threshold to counter sedimentation.