Ultrasound freeze casting: Fabricating bioinspired porous scaffolds through combining freeze casting and ultrasound directed self-assembly

Lightweight porous engineered materials are advantageous in a broad range of research fields because they combine desirable mechanical properties with the ability to leverage their porous structure. Existing techniques for fabricating porous material structures are limited by material choice, require multiple steps, and/or additional post-processing to create regions of varying material properties within the material structure, and are not easily scalable. In contrast, we implement and characterize a fabrication process for macroscale porous engineered material samples with a user-specified microstructure, by combining freeze casting, which allows fabrication of porous materials samples, with ultrasound directed self-assembly, which allows controlling the microstructure of the porous materials. We refer to this process as “ultrasound freeze casting (UFC),” and employ it to fabricate bioinspired materials that mimic the concentric rings of natural materials such as osteons and Liesegang rings. Specifically, we employ the UFC process to create material samples with three, four, and five concentric rings of alternating dense and porous TiO2 material. We find statistically significant differences of both the porosity and Vickers hardness when comparing the porous and dense regions of the material samples. These results will provide a new pathway to fabricate porous engineered materials with user-specified microstructure.