Synthesis of pumice doped hydroxyapatite nano- powders and investigation for bone repair

In the human body, small-scale damages in bones are spontaneously healed with regeneration, while conventional tissue transplantation methods are used in large-scale damages. However, these methods have serious limitations, such as tissue incompatibility and inflammation risks. Within the scope of tissue repair and Regeneration, the need for functional biomaterials with biocompatible and biomimetic properties is increasing. The inorganic structure of bone is mainly formed from hydroxyapatite (HA), a calcium phosphate compound with some ions at trace amounts e.g. carbonate, silicate, sodium, potassium and magnesium. Although HA plays a major role in bone repair, due to the high stability of synthetic pure HA its role in biodegradability and bone regeneration is limited. Pumice (PM) is an alumina silicate mineral formed as a result of volcanic activities and has properties such as high porosity and ion exchange. Within the scope of this thesis, the new ceramic forms were developed by doping of PM into HA during its production by the sol-gel method due to its high hardness, porous structure, ion absorption capacity and containing many ions found in bone, and their potential for bone regeneration were investigated. The ion exchange between PM and HA is aimed to enhance biosolubility and bioactivity of HA for bone regeneration by silicate and other biomimetic ionic additives. Silicate ions in pumice have the potential to promote bone mineralization. In addition, it is predicted that the porous structure of pumice will contribute to bone regeneration by triggering angiogenesis and facilitating cell migration and adhesion. PM powder was used after sizing and acid (HCl) - base (NaOH) activation purification processes. The pure HA samples in nano size and PM (acid-base activated) doped (2.5%, 5% and 7.5%, by weight) HA powders were produced and sintered at different temperatures (800°C, 950°C and 1100°C) and characterized by physical, chemical and biological means. Boron carbide (B4C), which is the hardest material known after diamond and reported to have superior strength and antibacterial properties, was physically bonded to PM-doped HA and its antibacterial activity was investigated. For this, 1% B₄C powder was added into 7.5% PM-HA powders sintered at 1100 °C and samples were produced after heat treatment was at 200°C and 800°C. While the morphological (SEM, S-TEM), chemical (XRF, XRD and EDX), biocompatibility (in-vitro cytotoxicity and confocal imaging) and in-vitro biodegradability tests of produced samples were performed in powders forms, the pressed dics samples were used for bioactivity, mechanical (microhardness) and antibacterial analyses. While pure HA crystals were in rod-like morphology, pumice mineral was dispersed in the HA matrix in the form of wide plates. Pure HA samples sintered at 1100 °C had a solid non-porous structure, while PM-HA samples (PM-HA) maintained their porous morphology at the same temperature. In EDX analysis, it was observed that PM-HA composite contained 1% Si, trace amounts of Na, K and Mg elements, as well as the main Ca and P elements. In XRD analysis, it was observed that tri-calcium phosphate phases were formed in PM-HA composites sintered at 950 °C and 1100 °C. In MTT cytotoxicity tests of sintered PM-HA composite by extraction, the maximum cell viability was obtained for samples sintered at 1100 °C. In bioactivity tests, carbonated apatite layer formation was observed on samples incubated in SBF for up to 7 days. In biodegradability tests, determination of calcium, phosphate, boron and silicon ions in samples kept in PBS for 15 days gave successful results for biodissolution. In conclusion, the investigation and characterization of pumice-doped hydroxyapatite composites have great potential for the development of innovative biomaterials that will support bone repair. These materials can be used in various areas, such as medical applications, bone fillings, bone grafts thanks to their biocompatibility and biodegradability properties.