We have previously shown the use of continuous liquid interface production (CLIP) 3D printing for the fabrication of porous lattices with various energy and biomedical applications [1]. We commonly observe a phenomenon known as overcure, in which resin becomes trapped and subsequently cured in the pores of the part, placing limitations on accessible feature sizes and void fractions. Injection of resin through the porous geometry via a technique known as injection CLIP (iCLIP) can be used to resolve sub-100 µm feature sizes [2,3]. However, determining injection schemes (flow rate, number, and location of injections) needed to successfully fabricate a given design and material system has heretofore required trial and error. To prevent overcure via iCLIP and thus resolve sub-100 µm negative spaces in 3D printed porous structures, we seek to combine the development of a transport model for the iCLIP 3D printing of porous geometries with a series of printing experiments.
We begin by developing an analytical model for fluid flow in the system, utilizing lubrication theory in combination with models for flow through porous media. We then confirm the accuracy of these analytical models via computational fluid dynamics. This model allows us to identify regions of stagnant fluid for systems of different porosities and viscosities, which we use as a first approximation for regions of potential overcure. We then study the effects of different injection schemes in reducing the volume of stagnant fluid in a given porous structure. Through simulation, we identify injection schemes that are promising in preventing overcure. Such schemes are then tested in experiments particularly focusing on porous tubes for artificial blood vessels and lattices for energy applications. We will discuss the success of these schemes and their implications for model development. Fluid mechanics modeling thus allows us to understand the physics of overcure, and offers significant promise in the rapid development of high-resolution 3D printed porous media for a broad range of designs and material systems.
References
[1] Onffroy, P. R., Chiovoloni, S., Kuo, H. L., Saccone, M. A., Lu, J. Q., & DeSimone, J. M. (2024). Opportunities at the Intersection of 3D Printed Polymers and Pyrolysis for the Microfabrication of Carbon-Based Energy Materials. JACS Au.
[2] Lipkowitz, G., Samuelsen, T., Hsiao, K., Lee, B., Dulay, M. T., Coates, I., ... & DeSimone, J. M. (2022). Injection continuous liquid interface production of 3D objects. Science advances, 8(39), eabq3917.
[3] Coates, I. A., Pan, W., Saccone, M. A., Lipkowitz, G., Ilyin, D., Driskill, M. M., ... & DeSimone, J. M. (2024). High-resolution stereolithography: Negative spaces enabled by control of fluid mechanics. PNAS, 121(37), e2405382121.