Investigation of the effect of nozzle design on rheological bioprinting properties using computational fluid dynamics

Abstract

Bioprinting is the utilization of techniques derived from three-dimensional printing to generate complex biological structures which may replace natural tissues or organs. It employs high spatial resolution deposition of different cell types, growth factors and biomaterials. Those together form bioinks, which are the bioprinting inputs, analogously to conventional inks with regard to inkjet printing. In extrusion bioprinting, continuous bioink filaments are deposited layer by layer on a surface by means of an extruder nozzle, employing the displacement of a piston or pneumatic pressure. If mechanical stresses applied on a cell membrane exceed a critical value, which depends on the cell type, the cell membrane may disrupt. Computational fluid dynamics (CFD) simulations of the bioink extrusion were done to evaluate shear stresses caused by the internal pressure of extruder nozzles during bioprinting. Different three-dimensional conical nozzle designs were tested by varying angles of convergence, lengths, input diameters and output diameters of the nozzles. The powerlaw model, with constants k = 109.73 Pa•s 0,154 and n = 0.154, was used to describe the expected non-Newtonian behavior of the bioink. Shear stresses and shear rates were evaluated for each nozzle design considering different pressures or velocities as boundary conditions at the nozzle entrance. The maximum wall shear stress value on each different nozzle varied between 1,038 Pa and 4,915 Pa. The results indicated which details of nozzle geometry are most relevant in order to optimize bioprinting. The best conditions for bioink rheology were also evaluated to ensure good printability and high cell viability.

Modeling the Three-Dimensional Bioprinting Process of β-Sheet Self-Assembling Peptide Hydrogel Scaffolds

“…Several studies already focused on the importance of simulating the extrusion of the biomaterial ink/bioink to predict the behavior of the material during the bioprinting phase ( 13 , 36 , 37 ).…”

“…In this scenario, finite element (FE) analysis is a powerful tool to investigate how those factors actually influence the extrusion-based bioprinting process of SAPHs, thus decreasing the trial and error experiments and material waste (13,(36)(37)(38). Simulating the material flow in the needle during the extrusion process allows to understand the relation between needle size, printing parameters, and material properties (13) and therefore facilitates the optimization of the printing parameters and the biomaterial ink/bioink formulation.…”

Computational Fluid Dynamics Assessment of the Effect of Bioprinting Parameters in Extrusion Bioprinting

“…Among these categories, extrusion-based bioprinting is the most used due to its relative simplicity, affordability, and scalability as high viscous materials with high cell density can be used. In extrusion bioprinting, continuous bioink filaments are deposited layer by layer on a surface mechanically by displacement of a piston or screw or using pneumatic pressure[ 2 ]. In contrast, inkjet bioprinting is comparable to conventional two-dimensional (2D) printing and cannot generate a continuous flow, whereas in laser-assisted bioprinting, a high-intensity laser is used to deposit the bioink without applying direct force to the cell and finally, stereolithography makes use of light-sensitive polymer material[ 3 ].…”

“…Magalhães et al . [ 2 ] looked at optimizing nozzle geometry through CFD simulation using wall shear stress as a measure of cell viability and concluded that convergence angle of the nozzle and exit diameter had the greatest effect on printability and cell viability. Emmermacher et al .…”

Improving Cell Viability and Velocity in μ-Extrusion Bioprinting with a Novel Pre-Incubator Bioprinter and a Standard FDM 3D Printing Nozzle

“…The internal geometry of the nozzle modifies inner bioprinting parameters such as pressure, velocity or shear stress which might have an important impact on the features of the bioprinted structures [ 30 ]. In this sense, computational simulation is commonly used to study inner bioprinting parameters [ 24 , 31 , 32 , 33 , 34 , 35 , 36 ] mainly due to the difficulty to perform experimental measurements without disturbing the flow of bioinks. Specifically, Reid et al [ 24 ], Gómez-Blanco et al [ 31 ] or Martanto et al [ 35 ] demonstrate that different conical tips gauges have a noticeable influence in the volumetric flow and the shear stress using numerical methods or computational simulations.…”