Understanding the 3D ice printing process for

Advances in 3D printing have enabled many applications across many disciplines, including medicine, manufacturing, and energy. A range of different materials can be used to print both simple foundations and fine details, allowing the creation of structures with tailored geometries.

However, creating structures with precise internal voids and channels at the microscopic scale still poses challenges. Scaffolds used in tissue engineering, for example, must contain a complex network of three-dimensional conduits that mimic the human vascular system. With traditional additive manufacturing, where material is deposited layer by layer, it is difficult to print such complex internal features without sacrificing time, precision, and resources.

To resolve this problem, Philippe LeDuc And Burak Ozdoganlarprofessors of mechanical engineering at Carnegie Mellon University, are leading the development of the 3D printing process for freeform ice (3D-ICE). The technique uses an on-demand 3D printing approach with water as a substitute for conventional printing inks. A piezoelectric inkjet nozzle ejects tiny water droplets onto a build platform held below freezing. This causes the droplets to freeze shortly after contact.

The process can be uniquely controlled to deposit one or more droplets before the previous one is frozen. This allows a water cap to remain on top of the printed structure and freezing progresses from the bottom. This allows for structures with smooth walls, transitions, and branches. Features as small as a human hair can be fabricated. As more droplets are deposited, an ice structure takes shape on the build platform. The diameter, height, and relative regularity of the pillar geometry can be adjusted by controlling the droplet deposition rate and the temperatures of the print surface, droplet, and workspace. If the build platform is offset such that the incoming droplet strikes at an angle, the freezing front will rotate accordingly, allowing for branched, curved, and overhanging structures that would be difficult or impossible to print with other 3D printing techniques without 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,” LeDuc said. “This could be useful in many areas, from creating new tissues to soft robotics.”

Since beginning As part of their project, LeDuc and Ozdoganlar’s ​​research team investigated ways to ensure that the 3D ice-making process is predictable and reproducible. In their recent paper published in the Proceedings of the National Academies (PNAS, Garg et al., 2024), they describe 2D and 3D numerical models to elucidate the physics behind 3D ice, including heat transfer, fluid dynamics, and the rapid phase change from liquid to solid during the printing process.

Their 2D models map the construction of straight pillars, including the respective effects of layered and smooth deposition. “The rate of droplet deposition affects the height and width of the structure,” Ozdoganlar explains. “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.”

Their 3D models map the construction of the oblique structures by predicting the rotation of the frost front. “There are all types of heat transfer, including conduction downward and convection to the surrounding area,” Ozdoganlar said. “All of these things are working simultaneously as you deposit each droplet. If you deposit obliquely, part of the droplet spreads to the side of the pillar before it freezes. And as you continue to deposit at that angle, the frost front slowly changes shape and the structure grows in that direction.”

In addition to further refining their mathematical models, LeDuc and Ozdoganlar’s ​​labs are now looking to expand 3D-ICE technology and explore its effectiveness in a range of applications. For example, current tissue engineering strategies often involve designing generalized tissues. 3D-ICE technology could soon make it possible to print personalized tissues that match the unique structure of each patient’s vascular system, meeting the specific needs of their body. In addition, 3D-ICE technology will make it possible to create functional tissue structures that can be used to understand different diseases or develop new therapies.

“When I started my lab, I never imagined that we would be 3D printing ice and using it to create tissues to help people,” LeDuc said. “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.”

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