Hardystonite-based bioceramics from preceramic polymer emulsions: Synthesis and application to scaffolds via Direct Ink Writing 3D printing

Bone tissue is a mineralized connective tissue that provides structural support to the body, protects soft tissues and vital organs, serves as a mineral reservoir, and houses mesenchymal stem cells. Despite its solid appearance, bone is a highly dynamic organ that undergoes continuous remodeling processes, essential for maintaining its structural and functional integrity and adapting to metabolic needs and environmental changes. Throughout life, every individual has a high risk of bone fractures, which can occur due to trauma, falls, or diseases. Fractures can be partial or complete, and the healing time varies based on several factors, including age, sex, type and severity of the injury, and the presence of other medical conditions. In simple fractures, bone has the ability to self-repair thanks to the synergy between osteoblasts, which form new bone matrix, and osteoclasts, which remove damaged bone tissue. However, in severe fractures caused by significant trauma or congenital defects, the bone cannot fully regenerate on its own and requires external intervention. A modern and emerging approach in this field is tissue engineering, which uses biomaterials to restore the functionality of the damaged bone portion, either through partial or complete replacement. Among the biomaterials that have garnered significant interest in recent years there is thardystonite, a bioceramic known for its excellent properties of biocompatibility, bioactivity, and ability to stimulate bone regeneration. Hardystonite is a calcium and zinc silicate (Ca2ZnSi2O7), known for its ability to support osseointegration and promote cell proliferation. This bioceramic is therefore particularly suitable for applications in bone tissue engineering. One of the main challenges in using hardystonite is its processing into three-dimensional porous structures, essential for bone regeneration. Porosity is a crucial factor influencing vascularization and cell infiltration into the scaffold, thus contributing to a better integration with natural bone tissue. To address this challenge, in this work hardystonite-based scaffolds were fabricated starting from an emulsion of preceramic polymers, exploiting the possibility to shape the material using additive manufacturing techniques. More precisely, the Direct Ink Writing (DIW) 3D 2 technique was used; this approach allows the creation of complex structures with precise control over porosity and geometry. In particular, two different inks were prepared, one with the addition of boric anhydride and the other without, to fabricate pure hardystonite and boron-doped hardystonite scaffolds and analyze the differences between them. Once the samples were printed, they were exposed to a UV lamp to complete their polymerization and finally subjected to controlled thermal treatment in air to convert the preceramic polymer into fully ceramic material. Subsequently, various tests were performed to evaluate the morphology, density, porosity, crystalline phases, and mechanical properties of the obtained samples. The results demonstrated that hardystonite-based scaffolds have an optimal porous structure and adequate mechanical properties to support bone regeneration. This study represents a small step forward towards the clinical use of hardystonite in tissue engineering, paving the way for new solutions for the treatment of bone fractures and skeletal defects.