Computational and experimental investigations of the mechanisms used by coaxial fluids to fabricate hollow hydrogel fibers

• Studied the influence of different operating conditions on the produce of hollow hydrogel fibers.
• Mathematical model for coaxial fluids which included the reaction–diffusion model was established.
• Used the VOF model to simulate the flow pattern in the process of making fibers.
• The inner diameter of hollow fibers was increased with the increase in viscosity of alginate and flow rate of CaCl2 solution.

Biological three-dimensional printing is a promising field of research, and offers potential for overcoming the main technological barriers to the fabrication of three-dimensional vascularized tissues and organs. One of the major methods to fabricate vascular-like networks that can support perfusion of nutrients and oxygen is the printing of hollow hydrogel fibers. In the present work, we investigate the effects of operating conditions on the dimensions of hollow hydrogel fibers and the interaction mechanism of coaxial fluids. The continuity equation and momentum equation integrated with the reaction–diffusion model established by Kim et al. [1] are used to establish a mathematical model of the fabrication of hollow fibers from coaxial fluids. The volume of fluid model by the computational fluid dynamics software package FLUENT 6.3.26 is applied to quantitatively simulate the flow pattern details. A stable liquid/liquid jetting co-laminar flow in the coaxial nozzle is obtained. In order to verify the validity of the simulation model, a coaxial nozzle is used to fabricate hollow hydrogel fibers under various flow rates. The results from simulations and experiments are consistent with each other.