Master Degree / Yüksek Lisans Tezleri
Permanent URI for this collectionhttps://hdl.handle.net/11147/3008
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Master Thesis The Effect of Surface Modification of Biomaterials on the Cellular Interactions(Izmir Institute of Technology, 2008) Özgür, Melek; Çiftçioğlu, MuhsinThe preparation and characterization of chitosan-hydroxyapatite composite scaffolds and protein adsorption chracteristics of these scaffolds have been investigated in this study. The effects of different chitosan/hydroxyapatite contents of the low density composites on the protein adsorption behaviour were experimentally examined.Bradford method at 595 nm and 280 nm UV protein absorption methods were used for the determination of adsorbed amount of bovine serum albumin (BSA) and human serum protein (HSP). In this study low molecular weight chitosan and hydroxyapatite have been used for the preparation of the scaffold composites by freeze drying and SEM was used for microstructural analysis. The thermal behaviour of the composites was investigated by DSC and TGA. Composite scaffolds were prepared by using different amounts of chitosan and hydroxyapatite (HA) and six different scaffolds were prepared and coded as C100H0, C80H20, C70H30, C50H50, C30H70, and C20H80. The porous low density scaffolds had 93.5-96.3% porosity with a slight increase in density with increasing HA content. The interconnected pore network was formed from 50-250 .m relatively uniform size pores with thin pore walls. The HA particles were fully embedded in the polymer matrix in the pore walls. The TGA curves have shown that the freeze dried phase seperation induced biopolymer sturucture degrates at lower temperatures faster than the original raw polymer. The adsorptions of BSA and HSP onto composites have been studied as a function of time, protein concentration and pH. Adsorption experiments were also conducted with commercial HA powder. The adsorption kinetics experiments have indicated that protein adsorption was almost completely achieved in the first 2-3 hours with relatively high uptake values of up to 45-60 mg/g and 40-60 mg/g for 595 nm Bradford and 280 nm methods. The adsorption behaviour did not fit to the commonly known Langmuir and Freundlich isotherms. This was attributed to the swelling/degradation tendency of the freeze-dried chitosan containing scaffolds. The HSP uptake of 30 and 50 wt% HA containing composites were in the 50-60 mg/g range which was higher than other composites and the raw unprocessed chitosan.Master Thesis Preparation and Characterization of Chitosan/Calcium Phosphate Based Composite Biomaterials(Izmir Institute of Technology, 2004) Yıldırım, Oktay; Çiftçioğlu, MuhsinIn this study the preparation and characterization of three-dimensional chitosan-calcium phosphate composite structures and porous hydroxyapatite bodies for biomaterial applications have been studied. The effects of chitosan calcium phosphate amount on density, porosity, microstructure, chemical composition and mechanical properties on the composites and effects of porosifier contents, hydroxyapatite content of the slurry and sintering temperature on density, porosity and microstructure of the porous ceramic samples were investigated. SEM was used for microstructural analysis, XRD and FTIR were used for chemical analysis, Archimedes method was used for investigating physical properties and compression test for investigating mechanical properties. In this study low molecular weight chitosan, -tricalciumphosphate, hydroxyapatite and hydroxyapatite whisker have been used. For composites freeze drying technique and for the porous bodies dry pressing, polymer sponge method and dough method have been used.The densities of the composites prepared by using chitosan as the matrix and hydroxyapatite, hydroxyapatite whisker, and B-tricalciumphosphate as reinforcement increased and the porosities decreased with the increase in the ceramic content. The modulus of elasticity and the yield stress generally increased with the increasing ceramic content except for the chitosan/-tricalciumphosphate composites. The densities and porosities of the composite structures varied in the range of 0.059-0.29 g/cm3 and 96-88% respectively. The elastic moduli of the composites varied in a range of 4.45-10.09 MPa and yield stress varied in a range of 0.14-0.34 Mpa due to the change in the ceramic weight%. Changing the ceramic weight% also had influence on the microstructure. Generally with increasing ceramic content the pore sizes decreased.The pore sizes varied in a range between 100-250, 100-400 and 100-200 for chitosan/hydroxapatite, Chitosan/-TCP/Hydroxyapatite and chitosan/HA whisker composites respectively. FTIR and XRD analysis showed that the composite structures contained original constituents, no new chemical compounds were formed the production process had not affected crystallinity of ceramic phases. The densities of the porous ceramic bodies decreased and the porosities increased with the increasing porosifier content at the porous ceramics prepared by dough method and dry pressing method. The porosity and density values of porous hydroxyapatite samples changed in range of 34-72% and 2.03 to 0.87 g/cm3. Pore sizes of polymeric sponge samples were found to be around 300-400 and dry pressing and dough method samples were found to be 10u.Master Thesis Synthesis and Characterization of Hydroxyapatite-Alumina Biocomposites(Izmir Institute of Technology, 2006) Şahin, Erdem; Çiftçioğlu, MuhsinThree component hydroxyapatite-alumina-zirconia composite presents a promising candidate material for bone replacement implants. Two methods were employed to synthesize the composite that is expected to have high bioactivity, high strength and high chemical stability in physiologic environment. Wet mixing and heterogeneous precipitation methods were used for the synthesis. Commercial hydroxyapatite, alum ina and yttria stabilized zirconia were mixed in varying proportions and obtained powders were sintered upto 1300 °C subsequent to dry pressing at 160MPa. An optimum composition of 10-20-70 volume percent zirconia, alumina and hydroxyapatite respectively was found to present the most suitable proportion in terms of sinterability and phase purity. -tricalcium phosphate formation at temperatures higher than 1150 °C was found to be the only source of impurity phase in the material.Heterogeneous precipitation method was applied to synthesize a composite material with a functionally graded structure. The three components were aimed to be coated on one another, zirconia (TZ-3Y) being the core, alumina being the intermediate layer and hydroxyapatite being the outer shell. The bulk composite was expected to have both enhanced mechanical properties and enhanced phase purity due to separation of two reactive phases, hydroxyapatite and zirconia by the alumina layer. The coating was done in two steps using urea as the precipitant, aluminum sulfate as the Al3+ source, calcium nitrate as the Ca2+ source and ammonium phosphate as the P source.Precipitation of aluminum hydroxides on TZ-3Y particulates and precipitation of calcium hydroxides as a nucleation point for hydroxyapatite on cores were facilitated through decomposition of urea above 85 °C in aqueous media. Particle size, distribution and morphology were monitored for alumina coated zirconia samples prepared with varying Al2(SO4)/Zirconia and urea/Al2(SO4) molar ratios. The sample prepared with stoichiometric Al2(SO4)/Zirconia ratio and urea/Al2(SO4) ratio 10 exhibited the most suitable composition and morphology for hydroxyapatite coating. Samples synthesized in the first step were used as cores for hydroxyapatite coating.Master Thesis The Densification and Sintering Behaviour of Molten Salt Synthesized Ha Whisker/Ha Composites(Izmir Institute of Technology, 2005) Bozkurt, Suat Bahar; Çiftçioğlu, Muhsin; Çiftçioğlu, MuhsinThe hydroxyapatite (HA) whiskers were used as reinforcements in the HA powder/HA whisker (HAp/HAw) composites. The HAw was synthesized with molten salt synthesis method (MSS). NaCl, K2SO4 and NaCl-K2SO4 fluxes and HA powders were used for the synthesis of HA whiskers. The effects of various salt/HA ratios, heat treatment temperatures and time were investigated. In order to enhance the dispersibility and the elimination of the powder agglomerates ultrasonic treatment was applied to the HA-salt powder mixtures before heat treatment. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques were used for the examination of the whiskers. The synthesized whiskers by using NaCl had a broad particle size range (0.25 to 40 mm in length and 0.2 to 20 mm in diameter) and similar morphologies. They had relatively larger diameters than those suitable for use as reinforcements in the HAp/HAw composites. The use of K2SO4 resulted in the formation of relatively uniform and thinner HA whiskers. The length and diameter of the whiskers varied from 5 to 90 mm and 0.5 to 10 mm, respectively. The whiskers prepared from NaCl-K2SO4 salt mixture were 12 to 110 mm in length and 0.5 to 25 mm in diameter. The HA whiskers, synthesized from NaCl-K2SO4 salt mixture and HA powder at 850°C, were selected as reinforcements for the composites because of their uniform morphology and dimensional properties. For the preparation of HAp/HAw composites, HA powder was ball milled and mixed with HAw in aqueous medium with the application of 2 h ultrasonic treatment. Sintering was carried out at 1200-1350°C range for 2 h. Pure HA powder shrunk more than the composites at all sintering temperatures and attained to 98.5% theoretical density at 1350°C. Although the density increases with sintering temperature, the density increase relative to the green structures decreases with whisker content at each sintering temperature. This may be attributed to the low shrinkage rate due to the presence of whiskers at high temperatures. The HA whiskers could be observed as embedded in the fine HA matrix for both slip cast and dry pressed samples from the SEM images. It was observed that the whiskers generally aligned in one direction except the 50% HAw-50% HAp composites.