Carnegie Mellon University Researchers have developed digital models that enable precise control of the 3D ice printing process in biomedical and manufacturing applications. The study was published in the Proceedings of the National Academies (PNAS).
Technological advancements in 3D printing have enabled its use in various fields, such as manufacturing, energy, and medicine. Structures with customized geometries can be created by printing intricate details as well as basic foundations using various materials.
However, designing structures with precise internal voids and channels at the microscopic scale remains a challenge. For example, scaffolds used in tissue engineering must have a sophisticated network of three-dimensional conduits that mimic the human vascular system. It is difficult to print such complex internal features with traditional additive manufacturing (where material is deposited layer by layer) without compromising time, accuracy, or resources.
Philip LeDuc and Burak Ozdoganlar, professors of mechanical engineering at Carnegie Mellon University, are leading the development of the 3D freeform ice (3D-ICE) process to solve this problem. In this on-demand 3D printing method, water replaces traditional printing inks. Tiny water droplets are ejected onto a build platform maintained at a subzero temperature using a piezoelectric inkjet nozzle. The droplets then rapidly freeze.
The process can be adjusted so that one or more droplets are deposited before the previous one freezes. The printed structure is covered with water on top and freezing begins from the bottom. This allows for the construction of structures with branched and transitional walls. Elements the size of a human hair can be created. On the build platform, an ice structure forms as more droplets are deposited. The diameter, height, and relative softness of the pillar can be modified by varying the print surface, the droplet and workspace temperatures, and the droplet deposition rate.
The freezing front will rotate based on the angle at which the incoming droplet hits the build platform. This allows for the production of branched, curved, and overhanging structures that would be difficult or impossible to print using conventional 3D printing methods without the use of additional support materials.
3D ice could be used as a sacrificial material, meaning we could use it to create precisely shaped channels inside manufactured parts. This could be useful in many areas, from creating new tissues to soft robotics.
Philip R. LeDuc, Professor, Department of Mechanical Engineering, Carnegie Mellon University
Since beginning work on this project, LeDuc and Ozdoganlar’s research team has been exploring ways to ensure the repeatability and predictability of the 3D ice-making process. They describe 2D and 3D numerical models to clarify the physics behind 3D ice, including heat transfer, fluid dynamics, and the rapid phase change from liquid to solid during the printing process.
Their two-dimensional models illustrate the process of constructing straight pillars, taking into account the impacts of smooth and layered deposits.
The rate of droplet deposition affects the height and width of the structure. If you deposit quickly, the water layer expands, producing wider structures. If you deposit slowly, the structure becomes narrower and taller. The substrate temperature also has effects. For the same droplet deposition rate, a lower substrate temperature produces taller structures..
Burak Ozdoganlar, Professor, Department of Mechanical Engineering, Carnegie Mellon University
Their 3D models use frost front rotation predictions to map the formation of oblique structures.
“There are all types of heat transfer, including conduction downward and convection to the surrounding area. All of these things are working simultaneously as you deposit each droplet. If you deposit at an angle, some of the droplet spills over the side of the pillar before freezing. And as you continue to deposit at this angle, the freezing front slowly changes shape and the structure grows in that direction,” Ozdoganlar said.
LeDuc and Ozdoganlar’s labs are currently working on extending 3D-ICE and studying its effectiveness in various applications, in addition to refining their mathematical models. For example, creating generalized tissues is a common strategy used in tissue engineering today. Soon, 3D-ICE could enable the printing of personalized tissues that adapt to each patient’s specific vasculature and meet their particular physiological needs. In addition, 3D-ICE will make it possible to create functional tissue structures that can be used for research into various diseases or the creation of new treatments.
When I started my lab, I never imagined that we would be 3D printing ice and using it to create tissues to help people. But our research has evolved. It’s brought together people like Burak and myself, and everyone brings all sorts of different perspectives and abilities. It’s a wonderful thing to do this work together, where the sum of the parts is definitely greater than the sum of the individual parts in this transdisciplinary science and engineering.
Philip R. LeDuc, Professor, Department of Mechanical Engineering, Carnegie Mellon University
Journal reference:
Garg, A., et al. (2024) Physics of 3D printing of freeform ice at microscale. Proceedings of the National Academies (PNAS). doi.org/10.1073/pnas.2322330121
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