Advancements in 3D Ice Printing with New Numerical Models

Carnegie Mellon University researchers have developed numerical models that allow precise control of the 3D ice printing process in biomedical and manufacturing applications. The study has been published in the Proceedings of the National Academies (PNAS).

Technological developments in 3D printing have enabled its use across 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 a variety of different materials.

Nonetheless, designing structures with precise, micro-scale internal voids and channels is still challenging. For example, scaffolds utilized in tissue engineering have to have a sophisticated, three-dimensional network of conduits that imitate the human vasculature. It is challenging to print such complex internal features with traditional additive manufacturing (where the material is deposited layer by layer) without compromising on time, accuracy, or resources.

Professors of Mechanical Engineering at Carnegie Mellon University Philip LeDuc and Burak Ozdoganlar are leading the development of the freeform 3D ice printing (3D-ICE) process as a solution to this problem. In this drop-on-demand 3D printing method, water is used in place of traditional printing inks. Tiny water droplets are ejected onto a build platform that is kept below freezing temperature using a piezoelectric inkjet nozzle. The droplets quickly freeze as a result.

The process can be adjusted so that one or more droplets are deposited before the preceding droplet freezes. The printed structure has a water cap on top, and the freezing starts at the bottom. This makes it possible to build structures with branching, transitioning walls. Human hair-sized features can be created. On the build platform, an ice structure forms as more droplets are deposited. The pillar's diameter, height, and relative smoothness can be altered by varying the printing surface, droplet, and workspace temperatures and the droplet's deposition rate.

The freeze front will rotate by the angle at which the incoming droplet strikes the build platform. This allows for the production of branching, 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, which means we could use it to create precisely-shaped channels inside of fabricated parts. That would be useful in a lot of areas, from creating new tissues to soft robotics.

Philip R. LeDuc, Professor, Department of Mechanical Engineering, Carnegie Mellon University

Since starting work on this project, LeDuc and Ozdoganlar's research team has been investigating ways to ensure the repeatability and predictability of the 3D ice process. They describe 2D and 3D numerical models to clarify the physics behind 3D ice, including heat transfer, fluid dynamics, and the quick phase change from liquid to solid during the printing process.

Their two-dimensional models depict the process of building straight pillars, considering the impacts of smooth and layered deposition.

The frequency of droplet deposition affects the height and width of the structure. If you deposit quickly, the water cap grows, producing wider structures. If you deposit slowly, then the structure becomes narrower and taller. There are also effects from the substrate temperature. 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 rotational predictions of the freeze front to map the formation of oblique structures.

“You have all types of heat transfer, including conduction to the bottom and convection to the surrounding area. All those things are working simultaneously when you deposit each droplet. If you deposit obliquely, part of the droplet spills over on the side of the pillar before it freezes. And as you keep depositing at that angle, the freeze front slowly changes shape, and the structure grows in that direction,” said Ozdoganlar.

The laboratories of LeDuc and Ozdoganlar are currently working to scale up 3D-ICE and investigate its effectiveness in various applications in addition to honing their mathematical models. For instance, creating generalized tissues is a common strategy used in tissue engineering today. Soon, 3D-ICE may enable the printing of customized tissues that fit the distinct vasculature of every patient and satisfy their particular physiological requirements. Furthermore, 3D-ICE will make it possible to create functional tissue constructs that can be used to research various illnesses or create novel treatments.

When I first started my lab, I would never have imagined that we would be 3D printing ice, and using it to create tissues to help people. But our research has evolved. It has brought people like Burak and myself together, and everyone brings all sorts of different perspectives and capabilities to the table. It’s a wonderful thing to do this work together, where the sum of the parts is definitely greater than 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 microscale freeform 3D printing of ice. Proceedings of the National Academies (PNAS). doi.org/10.1073/pnas.2322330121