Additive manufacturing of undoped and codoped β-tricalcium phosphate

Bone tissue is a highly vascularized dynamic tissue that has the ability to self-repair. However, in cases of pathologies such as trauma, osteoporosis and cancer, the bone is not able to re- establish its complete integrity. For this reason, tissue engineering in recent years has been working on the creation of synthetic substitutes that best reproduce the characteristics of natural bone. In order to obtain ideal scaffolds, it is necessary that the biomaterials used are biocompatible, bioresorbable and bioactive. In this thesis, a type of triply periodic minimal surface (TPMS), the Neovius, was created. TPMS are three-dimensional geometric surfaces that are characterised by two key properties: minimalism, whereby they have zero mean curvature at every point, and periodicity, whereby they repeat regularly in space. For the development of scaffolds based on TPMS structures, porosity plays a fundamental role. Optimal porosity has been shown to promote cell proliferation and efficient nutrient transport. Additionally, the porosity percentage and geometry of TPMS structures have been demonstrated to influence the mechanical properties of the scaffold, such as stiffness and compressive strength. Two distinct materials were employed in the fabrication of the scaffolds: undoped β-tricalcium phosphate and Mg-Sr-Ag-Cu (2.0-2.0-0.1-0.1 mol%) co-doped β-TCP. Beta-tricalcium phosphate (β-TCP or β-Ca3(PO4)2) is a polymorphic form of calcium phosphate that is widely used in the biomedical field, particularly as a material for bone regeneration and as a bone substitute in orthopaedic and dental treatments. It is highly biocompatible and bioactive, thereby promoting bone growth and integration with surrounding bone tissue. In contrast to other materials, β-TCP is gradually resorbed by the body, rendering it an optimal material for temporary implants and as a support structure for bone regeneration. However, the β phase is stable only at relatively low temperatures (up to approximately 1125°C), while the α phase becomes predominant at higher temperatures. Accordingly, co- doped β-TCP was employed in this thesis, with the expectation that the incorporation of cations will result in a delay to the phase transition. The samples were produced using Digital Light Processing (DLP) technology, a 3D printing technique that employs a digital projector to solidify entire layers of resin simultaneously. Subsequently, geometric measurements and density evaluations were conducted. Subsequently, the samples were subjected to heat treatments at various temperatures. A series of surface analyses were conducted in order to assess the quality of the printing and thermal treatments. Subsequently, mechanical tests were conducted. The co-doped β-TCP exhibited the capacity to delay the phase transition. This has an impact on porosity, density and volume, resulting in the fabrication of stronger structures when using this material in comparison to undoped β-TCP.