A Computational Fluid Dynamics Study of Material Deposition in Pneumatic Micro-Extrusion for Additive Fabrication of Bone Tissue Scaffolds

Pneumatic micro-extrusion (PME) presents challenges in achieving precise material deposition due to the small scale and high viscosity of the extruded material. Experimental methods alone often cannot capture the complex flow dynamics and interactions governing material transport in PME, underscoring the need for advanced computational modeling. This study establishes a 3D multiphase computational fluid dynamics (CFD) framework to simulate material deposition in PME, providing detailed insight into deposition behavior under varying process conditions. The CFD model, developed using ANSYS Fluent, is based on experimental boundary conditions defined to replicate pneumatic extrusion on a moving substrate. In this study, the effects of print speed and nozzle diameter are systematically investigated. Simulations revealed three deposition regimes: over-extrusion, normal extrusion, and under-extrusion. Lower print speeds produced over-extrusion with increased bead height and width, while normal extrusion maintained stable bead geometry. Higher speeds resulted in under-extrusion and discontinuities. Bead width decreased significantly between 10 and 15 mm/s, with discontinuities appearing at 20 mm/s. Besides, centerline velocity increased from 0.058 mm/s in the cartridge to 12.88 mm/s in the nozzle, closely matching experimental measurements (12.95 mm/s). Furthermore, pressure decreased slightly with increasing print speed, while nozzle velocity and wall shear stress remained unchanged. Additionally, nozzle diameter studies showed that smaller nozzles generated higher velocities and pressures, while larger nozzles produced broader but less cohesive deposition. Overall, these findings offer critical guidance for optimizing PME and improving scaffold fabrication for tissue engineering applications.