Master Degree / Yüksek Lisans Tezleri
Permanent URI for this collectionhttps://hdl.handle.net/11147/3008
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Master Thesis Green Synthesis of Nanostructured Bioactive Glass for Dental Applications(01. Izmir Institute of Technology, 2023) Tüncer, Melisa; Yücesoy, Deniz Tanıl; Öksel Karakuş, CeydaBioactive glass is a biomaterial commonly used in dental care products and bone tissue engineering applications due to its biocompatibility, bone-forming ability, and remineralization capability. Bioactive glasses form a hydroxyapatite-like layer on dentinal tubules by releasing calcium and phosphorus ions after interaction with saliva. Bioactive 45S5 glass traditionally synthesized by wet chemical methods which require high-temperature heating and the use of a strong acid catalyst, bringing into question of the possibility of introducing toxic acid residues into the final product. Therefore, there is a need to develop environmental-friendly bioactive glass synthesis methods or to modify existing ones in a way to uplift their environmental friendliness. To satisfy this need, we greenized the traditional sol-gel method by replacing the acid catalyst with an environment-friendly alternative and successfully used it for the synthesis of nanostructured 45S5 bioactive glass. First, physicochemical characterization of the synthesized bioactive glasses was performed. Then, the apatite formation capability of bioglasses were investigated in saliva. Next, the mineralization kinetics of bioglasses were tested in Ca/P buffer. In vitro toxicity tests were performed to assess the cytotoxic potential of the synthesized bioactive glass. All analyses were repeated for the traditional synthesis method for comparison purposes. The results confirmed that green synthesis is more advantageous in terms of bioactivity and functionality required for dental applications. Increasing the safety and functionality of bioglass at the same time during the production phase has critical importance for ensuring the sustainability of current applications as well as creating new uses in the biomedical fieldMaster 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 Sintered Ti-6a1 Powder Compacts(Izmir Institute of Technology, 2004) Çelik, Emrah; Güden, MustafaSintered Ti6Al4V powder compacts were prepared using atomized spherical and angular powders in the porosity range of 29-63%. Cylindrical green powder compacts cold compacted at various compaction pressures and then sintered at 1200 C for 2 h. The final porosities and average pore sizes were determined as functions of the applied compaction pressure and powder type. The compression deformation behavior of Ti6Al4V powder compacts was also investigated at quasi-static (1.6x10-3-1.6x10-1s-1) and high strain rate (300 and 900 s-1) conditions using conventional mechanical testing and Split Hopkinson Pressure Bar techniques, respectively. The mean pore size of the compacts varied between 29 and 171 Um depending on the particle size range of the powders used and the compaction pressure applied. Microscopic studies of as-received powders and sintered powder compacts showed that sintering at high temperature (1200oC) and subsequent relatively slow-rate cooling in the furnace transformed the microstructure of spherical powder from the acicular alpha to the Widmanstatten microstructure and angular powder from bimodal to equiaxed+ Widmanstatten microstructure.In compression testing, at both quasi-static and high strain rate conditions, the compacts failed primarily by shear band formation along the diagonal axis 45 C to the loading direction. Increasing strain rate was found to increase both the flow stress and the compressive strength of spherical powder compacts while it did not affect the critical strain for shear localization. The mechanical properties of angular powder compacts were further shown to be a function of powder size; larger the particle size higher the percentage of equiaxed structure while in compacts of particles <100 um relatively large voids resulted in reduced strength and ductility. Microscopic analyses of deformed but not failed and failed spherical powder compact samples further showed that fracture occurred in a ductile (dimpled) mode consisting of void initiation and growth in alpha phase and/or at the alpha/beta interface and macrocraking by void coalescence in the interparticle bond region. In angular powder compacts, the failure was granular brittle type at the interparticle bond region while the compact samples of particles <100 um fractured transgranularly through the voids. The strength of the sintered compacts was further shown to satisfy the strength requirements for cancellous bone replacement. The strength of the compacts having porosity level of 40% and/or lower was comparable with that of human cortical bone.Compared to Ti powder compacts of previous studies, Ti6Al4V powder compacts provided higher strength and increased porosity level of the compacts suitable for cortical bone replacement.Master Thesis Preparation and Characterization of Hydroxyopatite and Polymer Composite Biomaterials(Izmir Institute of Technology, 2002) Gültekin, Naz; Tıhmınlıoğlu, FundaIn the thesis, the preparation and characterization of polylactide-Hydroxyapatite(HA) composite films for biomaterial applications have been studied. The effects of number of parameters such as polymer type, HA loading, surface modification and its concentration on the mechanical, thermal microstructural and hydrolytic degradation properties of the composites were investigated. Four different types of polymers, Poly (L-lactide)(PLA1), 96/4 L-lactide,D-Lactide Copolymer (PDLA1), Poly (L-Lactide)(PLA2), and 67/23 Poly (L-Lactide-co-D,L-Lactide)(PDLA2), have been used. In this study, PolyLactide-HA composite films have been prepared by solvent-casting technique. The HA powder was synthesized by precipitation technique. Interfacial interactions between HA and polylactide polymer were modified to improve filler compatibility and mechanical properties of the composites by surface treatment of the HA with two different silane coupling agents; 3-aminopropyltriethoxysilane (AMPTES) and 3-mercaptopropyltrimethoxysilane (MPTMS) at three different concentration. Silane treatment indicated better dispersion of HA particles in the polymer matrix and improvements in the mechanical properties of the composites compared to the untreated HA loaded polylactide composites. Tensile test results showed that the maximum improvement in the mechanical properties of the composites was obtained for the PLA composites containing 1 wt % aminofunctional silane treated HA and 0.5 wt % mercaptopropyltrimethoxy silane treated HA for PDLA composites. Scanning electron microscopy studies also revealed better dispersion of silane treated HA particles in the polymer matrix. Thermal degradation kinetics of the composites was investigated and it was found that addition of HA into polymer matrix decreased the thermal degradation temperature and also slowed down the degradation rate. In this study, the hydrolytic degradation of poly (L-Lactide)(PLA), poly (L-Lactide-co-D-Lactide) (PDLA) and their hydroxyapatite (HA) loaded composites (10-50-w/w %) were investigated in simulated body fluid (SBF) at 37 0C and at pH 7.4 by in vitro static testing. Using different techniques, namely weighting to quantify water absorption monitored the hydrolytic degradation and weight loss, scanning electron microscopy (SEM) to observe morphological changes occurred at the surface of the films over time. At the end of the 150 days, only 12.5 wt % and 9.5 wt % of weight PLA1 and PLA2 were lost respectively. Degradation of the copolymers was faster than PLA1 and PLA2 and weight loss data of PDLA1 and PDLA2 were found to be nearly same with 17.5 wt % and 17 wt %, respectively. The changes of pH on all polymer were stable at 7.4, because of simulated body fluid indicates buffer solution properties. Degradation rate of PLA and PDLA composites containing 10 wt % HA decreased, and also water absorption of these samples increased. Weight loss decreased approximately from 12 wt % to 5 wt % and water absorption increased from 10 wt % to 13 wt % for PLA composites containing 10 wt % HA. The change of microstructural properties of obtained composites has been determined in simulated body fluid as a function of time. It was found that the surface of polymer composite films was coated with the calcium phosphate layer. This coating was increased with HA loading and ageing time.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.Master Thesis Designing and Manufacturing of Porous Spinal Cages Using Ti6a14v Foamed Metal(Izmir Institute of Technology, 2009) Dizlek, Mustafa Eren; Güden, MustafaOpen cell Ti6Al4V foams with varying porosities (50, 60 and 70%) were prepared at sintering temperatures between 1200 and 1350 °C using ammonium bicarbonate particles (315 - 500 .m) as space holder. Two different biomedical grade commercial, gas atomized spherical Ti6Al4V powders were used to prepare foams. Powder 1 was in size range of between 45 - 150 .m and Powder 2 in size range of between 30 - 90 .m. The foams were sintered under argon atmosphere in a tightly enclosed tube furnace. The resulting cellular structure of the foams showed bimodal pore size distribution, comprising macro pores (300 - 500 .m) and micro pores (1 - 30 .m). Compression tests of foam samples have shown that increasing sintering temperature or decreasing porosity increased the elastic modulus, yield and compressive strength and failure strain. The improvement in the mechanical properties of foams prepared using smaller size Ti6Al4V powder with bimodal particle distribution were attributed to the increased number of sintering necks and contact areas between the particles. The foam prepared with optimum porosity, pore size and mechanical properties for bone in-growth was further used to produce prototype porous spinal cages which are widely used in spinal surgery for vertebrae fixation. The geometries and size of the prototype spinal cages were determined through the measurements taken from human vertebrae. The foams for spinal cage preparation were first prepared in the form of plates and then core-drilled using water jet based on the design geometrical parameters determined for each vertebra segment.Master Thesis Determination of Material Constitutive Equation of a Biomedical Grade Ti6ai4v Alloy for Cross-Wedge Rolling(Izmir Institute of Technology, 2009) Kıranlı, Engin; Güden, MustafaIn the present work, the JC flow stress and damage parameters of a biomedical grade Ti6Al4V alloy that contained very low levels of interstitial elements were determined for the modeling its deformation in the CWR process. The JC models were determined through quasi-static (10-3-0.1 s-1) and high strain rates (300-1000 s-1) within the temperature range of 25-1150 oC. High strain rate tests were performed using both compression and tension SHPB testing devices. The damage model was determined using notched specimens of different stress triaxiality. The tested alloy flow stresses were found to increase with increasing strain rate for both compression and tension tests. This was proved that the alloy has a strain rate sensitive flow stress behavior. At increasing strain rates the failure strains in tension decreased. The reduced fracture strain was also confirmed by the microscopic observations. In statically tested samples the ductile fracture mode was composed of smaller but deeper dimples, while the dimples were observed to be shallow and larger in dynamically tested samples. The tensile fracture presumably started in a region and the b phase microscopically shown to deform plastically through the tensile axis. The compression failure mode of the alloy was found to be resulting from the shear band formation followed by the fracture of the shear band. High temperature test conducted at quasi-static strain rate showed that the stress values decreased greatly after about 800 oC due to a ->b transformation. Due to this two different JC material models valid between 25-600 oC and 800-1150 oC were developed. The determined JC parameters were found to be well agreed with the literature except the model obtained from the compression tests.