Alpha tricalcium phosphate-based hybrid bone analogs: assessment of cement behaviour and mechanical properties /

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2014
Alkan, Gözde
The main theme of this thesis was to establish materials science and chemical issues for developing a self-hardening cement system, for potential use in bone defect filling operations. The cement comprises of a ceramic powder  alpha-tricalcium phosphate (-TCP, -Ca3(PO4)2)  which hardens into inorganic ceramic part of the natural bone tissue, i.e. calcium deficient hydroxyapatite (CDHAp, Ca9(HPO4)(PO4)5(OH)) upon hydration. One of the primary objectives of this study therefore was, synthesis of phase pure -TCP by solid state reactions, and investigation of its’ hydraulic reactivity at around physiological temperature (37 °C) and evaluating the microstructural and mechanical changes upon cement conversion. These were accomplished by isothermal calorimetry studies and additional analytical characterization including x-ray diffraction, electron microscopy, chemical spectroscopy and mechanical testing. Additionally, in order to improve the strength of the hydration product, -TCP based hybrid cement blends were obtained by the addition of an inorganic (calcium sulfate hemihydrate, CSH, CaSO4½H2O) or an organic (polycaprolactone, PCL, (C6H10O2)n) component. -TCP:CSH and -TCP:PCL hybrid cements were again converted into CDHAp:calcium sulfate dihydrate (CaSO42H2O, CSD) or CDHAp:PCL cement-end products by hydration at 37 °C. For both systems, comparative and parametric studies were carried out to elucidate effect of these additives on hydraulic reactivity and mechanical properties of -TCP cements. It was found that CSH dramatically suppresses -TCP→CDHAp conversion and retards setting reaction. However, CSH addition significantly improves strength of cement-end products. The fracture strength of cement end product of pure -TCP was increased from 4.5±0.1 MPa up to 9.28±0.1 MPa upon addition of 25 wt. % CSH, as evaluated by diametral compressive tests. -TCP:PCL hybrids were also investigated in terms of reaction kinetics, microstructural and mechanical properties. Isothermal calorimetry analysis revealed that PCL postpones -TCP→CDHAp conversion as also evidenced by detailed microstructural and phase analyses. Meanwhile, PCL addition improved mechanical integrity of the hardened mass leading to a maximum fracture strength value of 6.54±0.1 MPa when added in optimum amount (3 wt. %).

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Citation Formats
G. Alkan, “Alpha tricalcium phosphate-based hybrid bone analogs: assessment of cement behaviour and mechanical properties /,” M.S. - Master of Science, Middle East Technical University, 2014.