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 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.Master Thesis Preparation and Characterization of Ha Powders-Dense and Porous Ha Based Composite Materials(01. Izmir Institute of Technology, 2002) Şimşek, Deniz; Çiftçioğlu, Muhsin; Şimşek, Deniz; Çiftçioğlu, MuhsinThe synthesis of hydroxyapatite (HA) powers, whiskers and preparation of HA based ceramics have been investigated in this work. Commercial HA powders were used for comparion purposes. The powder and sintered ceramics were characterized by optical microscopy, SEM,XRD, particle size determination, dilatometry and mechanical testing.Ca-P powders were synthesized by using (NH4)2HPO4 and Ca(NO3)2. 4H2O by aprecipitation method in aqueous medium. Ca/P ratio was set to 1,5 and 1,667 that yield the mixture of Ca-P phases and HA powder respectively at pH 10, 60 C and 24hrs aging. Ca/P ratio was set to 1,667 and the effect of pH of the medium, aging temperature and aging time on the powder characteristics was investigated. pH was set to 4,6,8,9,10 and 11 while aging temperature and time kept constant at 60 C and 24 hrs.Formation of HA powder was observed over pH 8. Agglomerated Monetite-Brushite powder was obtained at pH.4. Monodispersed prismatic Brushite crystals were obtained at pH.6. Aging temperature investigation was performed at 30-90 C at pH.10 for 24 hrs aging. Increase in the aging temperature led to formation of more thermally stable HA phase. Precipitates were aged for 0, 0.5, 1, 24 and 48 hours at constant pH.10 and temperature 60 C. Thermally stable HA phase was obtained over 24hr aging. All of the oven-dried precipitates were heat treated at 400-1250 C range in order to investigate the thermal stability and phase structure development. Optimum conditions for the precipitation of thermally stable HA powder was determined as pH.10, 60 C aging temperature and 24 hrs aging time that yields equaxed HA powder with particle size about 40-60 nm.Molten salt synthesis (MSS) and hydrothermal synthesis (HDT) were used to prepare HA whiskers. XRD patterns of both whiskers have shown that HA was the dominant phase in whiskers and no other phases were detected. Hydrothermal whiskers had submicron diameters with an average aspect ratio of 20. The diameter of the MSS whiskers were in the 1-5 micron range and were mostly hexagonal with an average aspect ratio of 10.10, 20 and 30 vol% whisker containing composites were prepared. Sintering behavior and mechanical properties were investigated. 98% TD of HA ceramics (3.16 g/cm3) was obtained in the 1150-12500C range. 80-90% TD was obtained at above 1200 C for the MSS whisker composites with very little shinkages. Densities of the HDT whisker containing composites were higher than those of the MSS whisker composites. The highest hardness value was determined as 537 Hv for the HA ceramics 1250 C sintered. Hardness of the composites was lower than that of pure HA powder based ceramics due to the presence of relatively high porosity. 10vol% MSS whisker addition yields comparable compressive strength (460-470 MPa) and elastic modulus values (14-17 GPa) with that of natural bone tissues (170-193 MPa compressive strength, 14-18 GPa elastic modulus).