Lithography-based 3D printing of multiscale scaffolds using zinc oxide tetrapods

Abstract

Zinc oxide (ZnO) has aroused great interest in recent years due to its multifunctional usability, particularly in the context of biomedical applications. A particular focus is on the use of tetrapodal ZnO micro- and nanoparticles, which have a unique 3D shape that is ideal for fabricating self-organized, highly porous micro-architected networks [1]. Due to their excellent degradability, t-ZnO networks can then serve as a sacrificial template for functionalization with low-dimensional nanomaterials such as graphene oxide (GO) or polymers like hydrogels [2]. Through etching the t-ZnO template so called aeromaterials can be obtained. Their open structure and tube-like arrangement transfer mere surface properties to volume properties with entirely new qualities emerging from this way of assembly.

Molding processes can quickly produce t-ZnO networks, but the resulting geometries are limited. The production of more complex structures, e.g., with undercuts or designed macroporosity, from pure t-ZnO has hardly been possible to date. These are vital, however, in applications like cell templates to grant cells and nutrients easy access to the networks. Developing a suitable additive manufacturing process for the fabrication of well-designed macroscopic structures with an inherent self-organized microstructure for biomedical or catalytic processes is, therefore highly desirable.

Here, we describe the development of a lithographic additive manufacturing process for processing highly filled t-ZnO slurries. Stable slurries could be developed by adapting the monomer composition, accompanied by rheological and sedimentation analyses, and the first scaffolds based on a gyroid design were manufactured with adapted printing parameters. Based on a thermogravimetric analysis, an appropriate thermal post-treatment protocol was established and final t-ZnO scaffolds with a self-organized microstructure were obtained. Scanning electron microscopy confirmed the highly porous microstructure of a t-ZnO network.

The scaffolds described here serve as a basis for further functionalization and show a promising approach for fabricating highly functionalized 3D-printed networks for biomedical applications.