Approach in crystallization of bone minerals

Bone is a complex, hierarchically structured composite material consisting of a mineral phase, an organic matrix, and water. The mineral phase is a calciumphosphate bioapatite which is structurally similar to hydro-carbonate-apatite. Collagen type I, but also non-collageneous proteins make up the organic matrix. Bone bioapatite contains many ionic substitutions compared to stoichiometric apatite, which results in variations of the apatite crystal lattice. Almost 100 years studying bone bioapatite have led to a great amount of literature, which is compiled, compared, and reviewed in the framework of this thesis. Besides, the impact of the organic matrix on the apatite crystal lattice in bone was investigated by analyzing deproteinized bone with Thermogravimetric analysis (TGA), and Fourier transform infrared spectroscopy (FTIR). For this purpose, the organic component of a powderized bovine femur was removed. Lattice parameters and crystallite size were analyzed by X-ray diffraction (XRD) including structural refinement (Rietveld analysis). FTIR was used to verify the organic and the carbonate content. In addition, the deproteinized bone was thermally treated in order to investigate changes of the deproteinized bioapatite unit cell as a consequence of heating. The result confirms the impact of the removal of the organics on the crystallographic structure of mammal bones. Furthermore, the bioapatite lattice parameters and crystallite size of mammal bones were studied for anatomical and species-dependent variations. Bovine, human, and sheep bones from different anatomical positions were analyzed by X-ray powder diffraction and Rietveld refinement and compared to the literature data. Moreover, the decomposition of the bioapatite in bone was investigated under acidic conditions (at pH values 4, 4.5 and 5), where brushite is the thermodynamically more stable calcium phosphate phase. Though, after fourteen weeks under acidic conditions, XRD analysis did not reveal any phase transformation. However, the acid-treated bones showed an increased compactness compared to non-treated bones. In order to investigate this, the bone surface was investigated by SEM and additionally, the chemical composition of non-treated and acid-treated bone was analyzed by EDX.