Freeze casting is a sophisticated and affordable method of manufacturing that creates highly porous materials with custom-designed hierarchical architectures, well-defined pore orientation, and multifunctional surface structures. Freeze-cast materials have a wide range of applications, including biomedicine, environmental engineering, and energy technologies.”An article in Nature Reviews Methods Primer now presents a comprehensive guide to freeze-casting methods, covering current and future applications as well as the characterization techniques, with a special focus on X-ray tomoscopy,” stated Prof. Ulrike Wegst, a materials scientist from Northeastern University and TU Berlin. The prestigious journal Nature provided the opportunity to prepare this primer, which was greatly appreciated by the research team.Dr. Francisco García-Moreno, Dr. Paul Kamm, Dr. Kaiyang Yin, and I, along with experts in tomoscopy, recently conducted in situ experiments and made new discoveries regarding ice crystal growth and templating. This led us to create a Freeze Casting guide for Nature Reviews Methods Primers (impact factor 39.8), combining experimental methods with techniques for process and materials analysis.
Using X-Ray tomoscopy to observe the process
We started by introducing different batch and con…The Primer offers an overview of the various characterization techniques for analyzing complex material architectures and properties, including continuous freeze casting processes and lyophilization. It also outlines the unique capabilities of X-ray tomoscopy, which allows for real-time 3D analysis of crystal growth and structure formation in polymers, ceramics, metals, and composites during solidification. This is especially useful for quantifying anisotropic crystal growth in aqueous solutions.
“and slurries, in which crystals extend in the different crystal directions at different velocities,” says García-Moreno.
From tissue scaffolds to porous electrodes
The freeze-casting process was developed more than 40 years ago for the production of tissue scaffolds. It quickly became evident that freeze-cast materials, because of their highly porous structure, could integrate effectively with host tissues and promote healing processes. Today, freeze-cast materials are extensively utilized not only in biomedicine but also in engineering, ranging from innovative catalysts to highly porous electrodes for batteries or fuel cells. A wide variety…ty of solvents, solutes and particles can be used to create the desired structures, shapes and functionalities.
What is the process of freeze casting?
To start, a substance is dissolved or suspended in a solvent, such as water, and then placed in a mold. Next, a specific cooling rate is applied to the copper mold bottom to solidify the sample in a directional manner. As the sample solidifies, there is a phase separation into a pure solvent, in this case ice, and a solute and particles, with the ice serving as a template for the solute/particle phase. Once the sample is completely solidified, the solid solvent is removed through sublimation during lyophilization. Lyophilis …The nation reveals a highly porous, ice-templated scaffold, which is a cellular solid with cell walls made up of the solute/particle that self-assembled during solidification. The size and number of pores, their geometry and orientation, the packaging of particles, and the surface characteristics of the cell walls, along with the mechanical, thermal, magnetic, and other properties of the material, can be customized for a specific application.
Outlook: New insights into the process under microgravity
To gain more information on the fundamental science of freeze casting, experiments will be conducted on the International Space Station.Ace Station planning for future research in freeze casting processes and custom-designed material manufacturing due to the effects of microgravity on structure formation in the ISS. This is expected to result in further advancements in understanding freeze casting processes and creating defect-free materials.
Reference:
Ulrike G. K. Wegst, Paul H. Kamm, Kaiyang Yin, Francisco García-Moreno. Freeze casting. Nature Reviews Methods Primers, 2024; 4 (1) DOI: http://dx.doi.org/10.1038/s43586-024-00307-5The link to the article is here.