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1. Computational Fluid Dynamics Modeling of Material Deposition in Pneumatic Micro-Extrusion Additive Manufacturing

   O’Malley, Ethan; Salary, Roozbeh “Ross” (July 2025, American Society of Mechanical Engineers (ASME) - International Mechanical Engineering Congress and Exposition (IMECE 2025))

   Pneumatic micro-extrusion (PME) presents inherent challenges in achieving precise control over material deposition due to the small scale and high viscosity of the material flow. Traditional experimental methods often fall short in capturing the complex mechanisms, interactions, and dynamics governing material transport and deposition in PME, highlighting the necessity for advanced computational approaches to unveil these intricate physical phenomena. The primary objective of this study is to develop a robust computational framework for simulating material transport and deposition in PME, offering detailed insights into the fluid dynamics, flow complexities, and deposition characteristics intrinsic to the PME process. This involves systematically investigating the influence of key process parameters, such as material properties, print speed, and flow pressure, on deposition dynamics. Three-dimensional (3D) computational fluid dynamics (CFD) modeling was employed using ANSYS Fluent, with boundary conditions defined to replicate pneumatic extrusion on a moving substrate. The CFD simulations captured three distinct deposition regimes: (i) under-extrusion, (ii) normal extrusion, and (iii) over-extrusion. Results show that decreasing print speed at constant inlet velocity produced over-extrusion, with increased bead height and width due to material overflow. At normal extrusion, bead geometry remained stable, while under-extrusion reduced bead width and ultimately led to discontinuities when flow stresses exceeded cohesive strength. Notably, bead width decreased significantly between 10 mm/s and 15 mm/s, but showed little difference between 15 mm/s and 20 mm/s. Instead, the higher speed produced discontinuities consistent with experimental observations. Centerline velocity profiles revealed that the flow inside the cartridge was very slow at approximately 0.058 mm/s, whereas the velocity increased sharply within the nozzle throat, reaching nearly 12.88 mm/s. These predictions were further supported by validation experiments, where the measured nozzle velocity of 12.95 mm/s closely matched the CFD-simulated value of 12.88 mm/s, demonstrating strong agreement between simulation and experiment. Additionally, pressure decreased slightly with increasing print speed due to reduced backflow, while nozzle velocity and wall shear stress remained unchanged under fixed inlet velocity conditions. Overall, the outcomes of this study are expected to inform parameter optimization strategies and enhance PME process efficiency, providing critical insights into how variations in PME process dynamics influence print morphology and quality, advancing the path toward optimized fabrication of scaffolds for tissue engineering applications. 

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2. A Roadmap to Fabricate Geometrically Accurate Three-Dimensional Scaffolds CO-Printed by Natural and Synthetic Polymers

   https://doi.org/10.1115/1.4055474  

   Quigley, Connor; Tuladhar, Slesha; Habib, Ahasan (June 2022, Journal of Micro and Nano-Manufacturing)

   Abstract Three-dimensional bioprinting is a promising field in regenerating patient-specific tissues and organs due to its inherent capability of releasing biocompatible materials encapsulating living cells in a predefined location. Due to the diverse characteristics of tissues and organs in terms of microstructures and cell types, a multinozzle extrusion-based 3D bioprinting system has gained popularity. The investigations on interactions between various biomaterials and cell-to-material can provide relevant information about the scaffold geometry, cell viability, and proliferation. Natural hydrogels are frequently used in bioprinting materials because of their high-water content and biocompatibility. However, the dominancy of liquid characteristics of only-hydrogel materials makes the printing process challenging. Polycaprolactone (PCL) is the most frequently used synthetic biopolymer. It can provide mechanical integrity to achieve dimensionally accurate fabricated scaffolds, especially for hard tissues such as bone and cartilage scaffolds. In this paper, we explored various multimaterial bioprinting strategies with our recently proposed bio-inks and PCL intending to achieve dimensional accuracy and mechanical aspects. Various strategies were followed to coprint natural and synthetic biopolymers and interactions were analyzed between them. Printability of pure PCL with various molecular weights was optimized with respect to different process parameters such as nozzle temperature, printing pressure, printing speed, porosity, and bed temperature to coprint with natural hydrogels. The relationship between the rheological properties and shape fidelity of natural polymers was investigated with a set of printing strategies during coprinting with PCL. The successful application of this research can help achieve dimensionally accurate scaffolds. 

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3. Controlling Porosity of 3D Bioprinted Scaffold: A Process Parameter-Based Approach

   Quigley, C.; Clark, S.; & Habib, M. A. (May 2023, Proceedings of the IISE Annual Conference & Expo 2023)

   Babski-Reeves, K; Eksioglu, B; Hampton, D. (Ed.)

   Extrusion-based 3D bioprinting is a promising method for repairing patient-specific tissues and organs due to its inherent capacity to release biocompatible materials containing living cells in a preset area. The filament geometry and width mostly determine the scaffold architecture. Extrusion pressure, print speed, print distance, nozzle diameter, and material viscosity are just a few of the process variables that can be carefully chosen to affect the filament shape and width, ultimately verifying the user-defined scaffold porosity. To maintain defined filament width variation for various hydrogels within an acceptable range and to confirm the overall geometric fidelity of the scaffold, in this paper, filament width for a set of biomaterial compositions was determined using an image processing technique and an analytical relationship, including various process parameters, was developed. 

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4. Systemic Control of 3D Bioprinting Process Parameters to Achieve Defined Scaffold Porosity

   https://doi.org/10.1115/msec2023-104235  

   Quigley, Connor; Tuladhar, Slesha; Adhikari, Samrat; Habib, MD Ahasan (June 2023, Proceedings of the ASME 2023 18th International Manufacturing Science and Engineering Conference (MSEC2023))

   Abstract Due to its inbuilt ability to release biocompatible materials encapsulating living cells in a predefined location, 3D bioprinting is a promising technique for regenerating patient-specific tissues and organs. Among various 3D bioprinting techniques, extrusion-based 3D bio-printing ensures a higher percentage of cell release, ensuring suitable external and internal scaffold architectures. Scaffold architecture is mainly defined by filament geometry and width. A systematic selection of a set of process parameters, such as nozzle diameter, print speed, print distance, extrusion pressure, and material viscosity, can control the filament geometry and width, eventually confirming the user-defined scaffold porosity. For example, carefully selecting two sets of process parameters can result in a similar filament width. However, the lack of availability of sufficient analytical relations between printing process parameters and filament width creates a barrier to achieving defined scaffold architectures with available resources. In this paper, filament width was determined using an image processing technique and an analytical relationship was developed, including various process parameters to maintain defined filament width variation for different hydrogels within an acceptable range to confirm the overall geometric fidelity of the scaffold. Proposed analytical relations can help achieve defined scaffold architectures with available resources. 

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5. Three-Dimensional-Printed Composite Structures: The Effect of LSCF Slurry Solid Loading, Binder, and Direct-Write Process Parameters

   https://doi.org/10.3390/ma17122822  

   Yang, Man; Parupelli, Santosh Kumar; Xu, Zhigang; Desai, Salil (June 2024, Materials)

   In this research, a direct-write 3D-printing method was utilized for the fabrication of inter-digitized solid oxide fuel cells (SOFCs) using ceramic materials. The cathode electrode was fabricated using the LSCF (La0.6Sr0.2Fe0.8Co0.2O3-δ) slurry loading and the Polyvinyl butyral (PVB) binder. The rheological parameters of slurries with varying LSCF slurry loading and PVB binder concentration were evaluated to determine their effect on the cathode trace performance in terms of microstructure, size, and resistance. Additionally, the dimensional shrinkage of LSCF lines after sintering was investigated to realize their influence on cathode line width and height. Moreover, the effect of the direct-write process parameters such as pressure, distance between the nozzle and substrate, and speed on the cathode line dimensions and resistance was evaluated. LSCF slurry with 50% solid loading, 12% binder, and 0.2% dispersant concentration was determined to be the optimal value for the fabrication of SOFCs using the direct-write method. The direct-write process parameters, in addition to the binder and LSCF slurry concentration ratios, had a considerable impact on the microstructure of cathode lines. Based on ANOVA findings, pressure and distance had significant effects on the cathode electrode resistance. An increase in the distance between the nozzle and substrate, speed, or extrusion pressure of the direct writing process increased the resistance of the cathode lines. These findings add to the ongoing effort to refine SOFC fabrication techniques, opening the avenues for advanced performance and efficiency of SOFCs in energy applications. 

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