DIRECT INK WRITING 3D PRINTING OF 70S30C BIOGLASS-BASED SCAFFOLDS SUPPORTED BY PRECERAMIC POLYMER EMULSIONS

Bone tissue is a mineralized and viscous-elastic connective tissue which acts as support of the body structure, protection of soft tissues and vital organs, minerals storage and source of mesenchymal stem cells. During a lifetime, any individual has an elevated risk of bone fractures, a medical condition due to trauma, falls or bone diseases, in which the bone is partially or completely broken. The time required for healing varies depending on several factors, such as the age and the sex of the subject, the type and severity of the injury or comorbidities. When dealing with simple fractures the bone is able to repair itself thanks to its self-healing ability related to the synergistic activity of osteoblasts, which produce new bone matrix, and osteoclasts, responsible for bone resorption. However, when dealing with severe fractures resulting from trauma or congenital defects, the bone is not able to repair itself anymore, but requires external intervention. A modern approach that is becoming increasingly popular in this field is Tissue Engineering which employs biomaterials to restore the normal functioning of the damaged portion through a partial or complete replacement of the latter. Among biomaterials that most firmly established in the last few decades we find bioactive glasses, a class of bioceramics, known for their characteristics of biocompatibility, bioactivity and bioresorbability. Bioactive glasses can be SiO_2, P_2 O_(5 )or B_2 O_(3 ) based; the formers are called silicate bioactive glasses and due to their low solubility are mostly used to repair bone tissue; the two latters are respectively called phosphate and borate bioactive glasses and they are characterized by a higher solubility which makes them suitable soft tissue regeneration strategies. Silicate bioactive glasses are perfect candidates for bone tissue regeneration due to their inherent ability to stimulate a beneficial reaction in the body, binding to bone tissue and undergoing a progressive dissolution while stimulating the body to produce hydroxyapatite. Nonetheless, the main limitation of bioactive glass 70S30C is the difficulty of being processed into porous 3D scaffolds without crystallizing during sintering. Therefore, to address this issue, the current thesis aims to produce 70S30C bioactive glass-based scaffolds supported by preceramic polymer emulsions. Preceramic polymers are used as precursors since, through a controlled heat treatment in oxidative or reduced atmosphere, they can be converted into ceramics. The main advantage in using preceramic polymers is the possibility to shape them using conventional polymer-forming techniques. Among these, additive manufacturing techniques, also known as 3D printing techniques, are met with enormous success in the tissue engineering field. This success is mainly attributed to the possibility of customizing patient-specific three-dimensional models to repair the affected region. In the present work the Direct Ink Writing 3D printing technique has been employed to produce 70S30C bioactive glass-based scaffolds (70%mol SiO_2 30%mol CaO). More specifically three different compositions of the ink were prepared by varying the percentage of water and for each of them five different shapes of scaffolds were produced with distinct levels of porosity: scaffolds 800-800, scaffolds 800-1600 and scaffolds 800-400 using a 0.84mm nozzle, scaffolds 400-800 and gyroids 500x500 using a 0.41mm nozzle. After that, to complete the polymerization and harden them further, they were exposed to an ultraviolet lamp and finally all of them underwent a controlled heat treatment in oxidative or reduced atmosphere to convert the preceramic polymer into a fully ceramic material. To conclude the study, the samples were measured and tested to assess the main characteristics such as morphology, composition, density, porosity, and mechanical properties in order to understand if the hypothesis advanced so far are confirmed.