The progress in 3D printing has facilitated several applications in various fields, such as medical, manufacturing, and energy. Various materials can be utilised to print both basic foundations and intricate features, enabling the construction of structures with customised geometry.
Nevertheless, the task of constructing structures with micro-scale, accurately defined interior voids and channels continues to present difficulties. Tissue engineering scaffolds must possess a three-dimensional intricate network of conduits that accurately replicate the human vasculature. In conventional additive manufacturing, which involves the gradual deposition of material layer by layer, it is challenging to produce detailed internal features without compromising on time, precision, and resources.
The 2D and 3D models accurately estimate the geometry of ice structures resulting from various parameters. Credit: Carnegie Mellon Unviersity, College of Engineering
Philip LeDuc and Burak Ozdoganlar, professors in mechanical engineering at Carnegie Mellon University, are leading the development of the freeform 3D ice printing (3D-ICE) technology to tackle this problem. This method employs a drop-on-demand 3D printing process use water as a replacement for traditional printing inks. A piezoelectric inkjet nozzle expels minuscule water droplets onto a build substrate that is kept at a temperature below the freezing point. This results in the rapid freezing of the droplets upon contact.
Remarkably, the process may be regulated to place a single or multiple droplets prior to the solidification of the preceding droplet. As such, a water cap remains atop the printed structure, and the freezing progresses from the bottom. This allows for the formation of structures characterised by seamless walls, smooth transitions, and interconnected branches. It is possible to create features that are as tiny as human hair.
As additional droplets are placed, an ice formation begins to form on the build platform. The pillar’s diameter, height, and smoothness can be modified by regulating the rate at which droplets are deposited and by adjusting the temperatures of the printing surface, droplet, and workspace.
Shifting the build platform to cause the droplet to hit at an angle allows for the rotation of the freeze front. This enables the production of complex structures such as branches, curves, and overhangs, which would be difficult or impossible to create using other 3D printing methods without additional support materials.
Representative example of a complex geometry produced using the 3D ice process. Credit: Carnegie Mellon Unviersity, College of Engineering
“3D ice has the potential to serve as a sacrificial material, allowing us to create accurately-shaped channels within manufactured components,” stated LeDuc. “This would have broad applications, ranging from tissue engineering to the field of soft robotics.”
From the beginning of their study, the research team led by LeDuc and Ozdoganlar has been exploring methods to guarantee the predictability and replicability of the 3D ice process. The authors of the latest research published in the Proceedings of the National Academy of Sciences (PNAS) employ 2D and 3D numerical models to explain the underlying physics of 3D ice. This includes analysing heat transmission, fluid dynamics, and the quick transition from liquid to solid state that occurs throughout the printing process..
Their 2D models map the construction of straight pillars, including the respective effects of layered and smooth deposition. “The frequency of droplet deposition affects the height and width of the structure,” said Ozdoganlar. “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.”
Their 3D models accurately depict the formation of slanted buildings by forecasting the rotation of the freezing boundary. “There are various forms of heat transfer, such as conduction towards the bottom and convection towards the surrounding area,” stated Ozdoganlar. “All those factors are operating concurrently when you deposit each droplet.” When you place the droplet at an angle, a portion of it flows over onto the side of the pillar before it solidifies. As you continue to deposit at that angle, the freeze front gradually alters its shape, causing the structure to expand in that particular direction.
LeDuc and Ozdoganlar’s laboratories are currently focusing on enhancing their mathematical models and expanding the use of 3D-ICE to various applications. Currently, tissue engineering procedures frequently entail the creation of generalised tissues.
3D-ICE has the potential to enable the production of customised tissues that accurately replicate the distinct vasculature of individual patients, thereby addressing the precise requirements of their bodies. In addition, 3D-ICE will facilitate the production of functional tissue constructs that can be utilised for comprehending various ailments or formulating novel therapies.
“At the inception of my laboratory, I could not have fathomed that we would be utilising 3D printing technology to fabricate ice and employ it in the production of tissues for the purpose of aiding individuals,” stated LeDuc.
“However, our research has progressed.” It has facilitated the connection between individuals such as Burak and myself, and each person contributes diverse viewpoints and skills. Collaborating on this task is a remarkable endeavour, as the collective outcome surpasses the contributions of each individual in this interdisciplinary field of science and engineering.
