Biomaterial flow modeling beyond the nozzle: A rheological perspective

Achieving optimal printability is the key hurdle in extrusion-based 3D printing for medical use. Predicting printability before conducting costly and time-consuming physical experiments is necessary to save valuable biomaterial. This can be done with numerical models. An accurate viscosity model should be incorporated into numerical models to accurately represent biomaterial behavior under shear. Time-averaged and time-dependent viscosity models are available in the literature and can predict material behavior under shear. Here, the power-law and lambda-thixotropic viscosity model curves are obtained from experiments on the same biomaterial. Optimal model coefficients for the lambda-thixotropic viscosity model are obtained by computationally modeling the rheometer plate gap in 2D and solving the resulting equations using a Computational Fluid Dynamics (CFD) model. The performance of the power-law (time-averaged viscosity) and lambda-thixotropic viscosity models is qualitatively examined by incorporating them into the CFD model. To achieve a trade-off between accuracy and computational speed, a time-averaged viscosity model is used in a three-dimensional CFD model. A three-dimensional CFD model employs the Volume of Fluid method within the Finite Volume Method framework to investigate flow behavior outside a single nozzle. Simulations are carried out using a three-dimensional CFD model to assess the stackability of the biomaterial on the substrate. Additionally, the ability to print biomaterials one after another is evaluated.