An Experimental and Numerical Study on Coaxial Extrusion of a Non-Newtonian Hydrogel Material

Abstract

Coaxial extrusion is a commonly used process to manufacture tubular structures to mimic vascular systems in 3D bioprinting. In this study, the stability of coaxial extrusion of a non-Newtonian material, Pluronic F127, is investigated. The extrusion process is considered stable when the extrudate form a core-annular structure. When it is unstable, dripping or jetting of the inner fluid is observed. In this study, the effects of the viscosity ratio, flowrate ratio, and the non-Newtonian behaviors on the stability of the coaxial extrusion process are investigated experimentally and numerically. The results show that all three factors can affect the stability of the process. When the ratio of viscosities increases, the process becomes unstable. The extrusion process tends to be stable when the flowrate of the outer fluid is much higher than that of the inner fluid. When the overall flowrate decreases, due to the non-Newtonian fluid behavior, the extrusion process can become unstable. This study shows the interconnected relationship between viscosity, flowrate, and non-Newtonian fluid behaviors and their effects on the stability of the coaxial extrusion process. The non-Newtonian flow behavior needs to be considered when studying or using coaxial extrusion. This study also provides a guiding principle on how to alter extrusion parameters in order to achieve the desired flow pattern.