Effects of Calcium Oxide Precursors and Photocurable Resin Feedstocks on 3D Printed SiO₂/CaO Bioactive Glass Scaffolds

The purpose of the musculoskeletal system is to support the body, protect internal organs and enable locomotion. Bone tissues can remodel themselves thanks to osteoclasts and osteoblasts’ action in order to adapt the tissue to the natural change in loading conditions and biological environment that occurs throughout life. Various diseases and traumatic events can alter homeostasis in this tissue, such as a fracture, removal of a portion of bone tissue or weakening of the matrix due to the onset of osteopenia or osteoporosis. Research in the field of biomaterials for bone tissue repair focuses on the discovery and improvement of innovative second and third-generation bioactive materials that not only mechanically support damaged bone but also stimulate the body itself to produce new healthy tissue through the degradation and release of osteoconductive and osteoproductive chemical molecules. One of the most important biomaterials are bioceramics, which are inorganic materials classified as either bioinert (e.g. Zirconia and Alumina) or bioactive (e.g. Bioglasses, Hydroxyapatite, Tricalcium phosphate) based on their interactions with host tissues. Bioceramic materials are widely used in bone regeneration thanks to their biocompatibility, biodegradability, bioactivity, and osteoconductivity. Bioglasses are amorphous materials that are biocompatible and can bond with natural bone tissue, promoting the growth of bone tissue. These materials are primarily composed of SiO2, Na2O, CaO, and P2O5 ions. Bioglasses can be formed into structured, porous, three-dimensional scaffolds or used in powder form to coat other materials or as fillers in composite materials. The first bioactive glass, known as Bioglass® and belonging to the SiO2-Na2O-CaO-P2O5 system, was synthesized 55 years ago by Hench. The composition of 45S5 Bioglass® includes 45% SiO2, 24.5% Na2O, 24.4% CaO and 6% P2O5 by weight. Silicate bioactive glasses are ideal for bone tissue regeneration because they naturally stimulate a positive biological response, bind to bone tissue, and gradually dissolve, prompting the body to generate hydroxyapatite.The scaffolds that will be presented in this thesis, were made with the polymer-derived ceramics technology also called PDC. Polymer-derived ceramic (PDC) technology uses synthesized preceramic polymer precursors that, after or during forming, undergo cross-linking which is then followed by pyrolysis to produce ceramics. This technique enables the fabrication of high-performance ceramics that are difficult to achieve with conventional ceramic methods. The current thesis aims to create SiO₂/CaO Bioactive Glass Scaffolds using the Direct Ink Writing 3D printing technique. Specifically, the goal is to understand which photocurable resin and which calcium precursor is best suited to create SiO₂/CaO bioglass. Different compositions of the ink were made by varying the photocurable resin (Funtodo and Prusa Tough), the calcium precursor (Calcium Nitrate Tetrahydrate, and Calcium Acetate), and the percentage of water. Each composition, then, has been printed into 800-800 scaffolds using a 0.84mm nozzle. After printing, each scaffold was exposed to Ultraviolet Light using a UV lamp to harden it and to complete the polymerization process. Finally, all of the samples underwent a controlled heat treatment in an oxidative atmosphere to convert the preceramic polymer into a fully ceramic material. Only 70S30C (70% mol SiO2, 30% mol CaO) scaffolds have been tested to determine the main characteristics such as morphology, composition, density, porosity, and mechanical properties.