Optimal design of multi-biomaterials mixed extrusion nozzle for 3D bioprinting considering cell activity

The uneven mixing of high-viscosity inks and cell damage caused by high-shear stress during the mixing extrusion process has persistently posed challenges to its extensive application in tissue engineering. To reconcile the conflict between mixing efficiency and shear stress, this study employed computational fluid dynamics to analyse the flow behaviour and mixing processes of the hydrogel solutions in a mixing extrusion nozzle. Results indicate that with the inclination of the mixing blade, reduction of the outlet diameter, and increase in printing speed, the shear stress within the channel significantly escalates. The mixing efficiency of the mixer is solely related to its structure and is independent of the flow velocity. Following, an optimised mixing blade structure and a computational method were proposed to evaluate the performance of the mixer. Finally, an empirical equation was established relating the maximum shear stress to the outlet nozzle diameter and printing speed.