Phd Degree / Doktora

Permanent URI for this collectionhttps://hdl.handle.net/11147/2869

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COAR Access Rights: search.filters.coarAccessRights.open accessSubject: search.filters.subject.Calcium phosphate

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  • Doctoral Thesis
    Synthesis and Characterization of Calcium Phosphate Cement Based Macroporous Scaffolds
    (Izmir Institute of Technology, 2012) Şahin, Erdem; Çiftçioğlu, Muhsin
    The goal of this thesis is to synthesize unique, clinically relevant macroporous calcium phosphate cement blocks to be utilized both in vivo and in vitro tissue engineering applications. Calcium phosphate cements which essentially consist of hydroxyapatite or brushite are constantly improved to overcome their inherent shortcomings such as low strength, low functional porosity, and low resorption. Recent literature on the topic points to monetite forming cements as an alternative phase. A novel method to utilize monetite that is finer and stronger with respect to brushite in load bearing scaffold applications is introduced in the results section of this thesis as a contribution to ever growing literature on this scope. In the preliminary study on the conversion extent of apatite forming cement, ionic strength of the setting liquid was determined as the prime effective factor on monetite conversion extent. Subsequently brushite forming β-tricalcium phosphate – monocalcium phosphate monohydrate cement system was modified by NaCl and citric acid so that brushite formation was selectively inhibited. Singular and synergistic monetite promoting effects of NaCl and citric acid were determined by monitoring the kinetics of cement setting in excess setting liquid. Spectrometric studies revealed the difference in brushite and monetite crystal surface site density which enabled selective inhibition of brushite and promotion of monetite by the synergistic effect of NaCl anc citric acid. Proposed phase control mechanism enables tailoring the composition of biphasic cements comprising of a predetermined monetite content and brushite or hydroxyapatite. In the final stage of the thesis, size distributed NaCl particles were introduced into the cement paste containing optimum amount of citric acid to enable complete monetite formation. Resultant macroporous monetite blocks were characterized in terms of microporosity, macroporosity, density, morphology, strength, phase composition, and surface area. Interconnectivity of the cement was optimized based on the correlation of porogen size distribution and morphological data.
  • Doctoral Thesis
    Preparation and Characterization of Resorbable Calcium Phosphate Based Bioceramics
    (Izmir Institute of Technology, 2010) Çetin, Ali Emrah; Çiftçioğlu, Muhsin; Çiftçioğlu, Muhsin
    The main objective of this study was to determine the behavior of hydroxyapatite powders in solutions containing major ions found in human blood plasma. Research efforts however were focused on two different fields, chemical analysis and dissolution testing of hydroxyapatite. Arsenazo III-calcium analysis method was selected and modified for the low level calcium analysis whereas malachite green phosphate assay was used for phosphate determinations. Arsenazo III reagents with different dye concentrations and pH values were tested for the analysis of low levels of calcium. The effects of ions at their blood plasma concentration levels on the modified calcium analysis method were further evaluated. Effects of these ions on the accuracy of phosphate analysis by malachite green assay were also investigated. Dissolution behavior of synthesized and commercial hydroxyapatite was investigated by immersing pellets in several solutions. Calcium and phosphate release kinetics in ultrapure water, sodium chloride and sodium bicarbonate solutions were investigated. Commercial hydroxyapatite pellets were also immersed separately in magnesium chloride, and sodium chloride/bicarbonate solutions. Calcium concentrations in solutions were found to decrease in the following order: sodium chloride > ultrapure water > bicarbonate. Phosphate concentrations in solutions were found to follow an order of sodium bicarbonate > sodium chloride > ultrapure water. Bicarbonate-phosphate ion exchange was observed in bicarbonate ion containing solutions. Magnesium-calcium ion exchange and adsorption of phosphates on hydroxyapatite surfaces were found to be effective in magnesium ion containing solution.