Ice 3D printing process could produce new biomedical and electronic devices with complex internal channels

Researchers from Carnegie Mellon University have developed a method for 3D printing microscale ice structures that can be used as sacrificial models to form complex channels inside other parts.

This “upside down” 3D printing process involves shooting water droplets onto a custom-built platform capable of freezing them upon landing at -31°F. These smooth, supportless ice sculptures can then be dipped in resin and hardened, melting them, leaving behind pieces with intricate internal pathways.

According to the team, the technology has the potential to produce devices with fully fledged networks of liquid or airflow conduits, including anything from soft robots capable of safely interacting and non-invasive way with patients, flexible electronics and bio-imitation of human tissue with venous channels.

“Using our 3D ice process, we can fabricate microscale models of ice with smooth walls and branching structures with smooth transitions,” explained Akash Garg, project researcher and mechanical engineering student at Carnegie Mellon University. “These can then be used to fabricate microscale parts with well-defined internal voids.”

Diagrams of the team’s reverse molding process and some of their prototype prints. Photos via Carnegie Mellon University.

3D printing of ice: an emerging field

Designed to allow fluids to pass through a part’s structure, internal channels are often used in 3D printed products with thermal control applications like heat exchangers, or on a smaller scale, in laboratory biomedical devices. on chip. However, removing any excess material stuck inside such objects can be difficult, even with continued improvements in post-processing.

One way to approach this problem, which is gaining traction in the research community, is to 3D print models of ice that can be embedded into objects before being melted. At China Peking University in 2019, scientists developed a voxel-based ice 3D printing methodin which each voxel can be projected as a blob or clump, to create complex alphabet-like structures.

Going back to 1999, scientists from Tsinghua University and the New Jersey Institute of Technology even experienced with a 3D printing of quick-freeze prototypes process of constructing larger, centimeter-scale structures. In practice however, these approaches have struggled to match the production of objects with smooth surfaces and microscale features. The latter, in particular, also suffered from a delay between deposition and freezing, which made it difficult to print without supports.

A diagram showing how the researchers' Freeform ice printing process works.  Image via Carnegie Mellon University.
A diagram showing how the researchers’ free-form ice printing process works. Image via Carnegie Mellon University.

An “inside-out” approach to 3D printing

In an effort to make 3D printing on ice more viable, the Carnegie Mellon team has now built its own 3D printer, consisting of a temperature-controlled platform mounted on an XY stage with a Micro Fab inkjet print head. Using frequency modulation of droplet ejection, this device theoretically allows the jet to be synchronized with the movements of the scene, thus allowing the creation of parts with a smooth surface.

By initiating a rapid liquid-to-solid phase change, the system is also able to do so without the need for supports, while conducting the process inside an acrylic enclosure allows it to be conducted in a way that prevents the formation of frost.

To put their system to the test, the researchers first attempted to 3D print narrow, angled pillars, but excessive platform movement caused many of the droplets to miss their target and start darting. new constructions. Using the data from these tests, however, the scientists found that they could develop pre-programmed step trajectories that produced structures with curved geometries and cantilevers of up to 80°.

After replicating these tests to create a series of increasingly complex 3D geometries, the team then evaluated their effectiveness as sacrificial models. This process saw a set of 3D printed ice sculptures immersed in Henkel Loctite 3971 resin, which had been pre-cooled to prevent it from melting instantly. Yet even so, the initial patterns melted away, displacing the internal channels of the resulting piece.

However, by controlling the light intensity during hardening, the team was ultimately able to prevent the ice from melting until the parts were complete, before evaporating it, to leave preserved lanes with a deflection of just 3 µm. After demonstrating that their reverse molding process is “orders of magnitude faster” than other microfluidic 3D printing methods, the scientists say it could meet multiple medical applications.

“This is an incredible achievement that will bring exciting breakthroughs,” added Burak Ozdoganlar, professor of mechanical engineering at Carnegie Mellon University. “We believe this approach has enormous potential to revolutionize tissue engineering and other fields, where miniature structures with complex channels are in demand, such as for microfluidics and soft robotics.”

Some of the team's leaning 3D printed pillar samples.  Photos via Carnegie Mellon University.
Some of the team’s leaning 3D printed pillar samples. Photos via Carnegie Mellon University.

Microfluidic 3D printing in medical R&D

Thanks to micro-scale 3D printing, it is becoming increasingly possible to develop microfluidic devices with integrated channels that have the potential to facilitate advances in biomedical R&D. At Stevens Institute of Technologyfor example, scientists have turned to microfluidics-based 3D bioprinting to support broader efforts to develop 3D printed organs.

Earlier this year, it was also announced that new 3D-printed microfluidic devices from Phase and Virginia Tech could help researchers formulate new and improved medical treatments for conditions such as brain cancer. Having obtained a scholarship from National Center for the Advancement of Translational Sciencesthe duo also aims to develop a way to streamline drug discovery.

Researchers at University of Bristol, meanwhile, have developed a low-cost open-source microfluidic 3D printing method. Requiring only everyday hardware, a desktop 3D printer, and free software, the process is designed to reduce complexity and barriers to entry in microfluidic device fabrication.

The researchers’ findings are detailed in their paper titled “Free-form 3D ice printing (3D-ICE) on a micro scalewhich was published by Akash Garg, Saigopalakrishna S. Yerneni, Phil Campbell, Philip R. LeDuc and O. Burak Ozdoganlar.

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The featured image shows diagrams of the team’s reverse molding process and some of their prototype prints. Photos via Carnegie Mellon University.