Master Degree / Yüksek Lisans Tezleri
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Master Thesis Effects of Zirconia and Hydroxyapatite Nanoparticles on the Mechanical Properties of the Resin-Based Dental Composites(01. Izmir Institute of Technology, 2023) Tunca Taşkıran, Senagül; Tanoğlu, MetinThe majority of the population suffers from dental caries, one of the most common chronic diseases. Therefore, restoration of teeth is an urgent need. The materials used in restoration are composites prepared by adding inorganic components to the polymeric matrix. However, failure due to fractures and secondary caries is still the main problem. Therefore, studies are continuing to improve the mechanical properties and water sorption and solubility properties of the composite. In this study, effects of zirconia, which improves the mechanical properties, and hydroxyapatite nanoparticles, which are the components of the tooth, on the mechanical properties of the composite were investigated. According to the literature, amounts of additives were determined as 1 and 2 wt.% for zirconia and 3 and 5 wt.% for hydroxyapatite. Nine different composites were prepared by mixing with hand spatulation method and mortar mill. The flexural strength and modulus, compressive strength, depth of cure, water sorption and solubility properties of the composites were investigated. Samples were characterized by using Scanning Electron Microscopy (SEM) and Fourier Transform Infrared Spectroscopy (FTIR). Zirconia and HA particles significantly improved the flexural and compressive strength of the composites. The highest flexural strength was obtained in the sample containing 5 wt.% hydroxyapatite and 1 wt.% zirconia, with an increase of 58% compared to the control sample. The highest compressive strength was obtained in the sample containing 3 wt.% hydroxyapatite and 2 wt.% zirconia, with an increase of 22% compared to the control sample. Therefore, zirconia and HA nanoparticles have a synergistic effect.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 The Preparation and Characterization of Hydroxyapatite Bioceramic Implant Material(Izmir Institute of Technology, 2000) Çiftçioğlu, Rukiye; Harsa, Hayriye ŞebnemThe use of hydroxyapatite (HA) powders and ceramIcs as a biomaterial was investigated in this work. A commercial HA powder was used for the preparation of HA ceramics and the adsorption of Bovine Serum Albumin (BSA) onto HA has been investigated.The powder and the sintered ceramics were characterized by TGA, DT A, Optical Microscopy, Microhardness Tester, XRD, and FTIR.The sintering studies have shown that it was possible to prepare porous ceramics above 800°C and dense ceramics at 1200-1250°C range.The HA powder lost about 5.5% by weight during heat treatment up to 1000DC and 80% of this weight loss is due to adsorbed water.The particle size of the powder was determined to be submicron whereas the grain sizes of the 1250°C sintered ceramic was in the 1-5 /l um range.A maximum Vickers Hardness of 585 Hv was determined for the 1250°C sintered 97.2% dense ceramic.XRD patterns of the powder and the 1250°C sintered ceramic were identical and almost phase pure. A small CaO peak was detected in the samples which was believed to be remnants of the powder preparation process.The adsorption of BSA onto HA has been studied as a function of time, protein concentration, pH, ionic strength, and HA solids loading. Adsorption experiments were also conducted with commercial alumina and zirconia ceramic powders. Uptake curves have shown that the adsorption process was almost completed in less than ten minutes Adsorption isotherms 'at different pH ( 4.5-7.4) have been obtained and analyzed using the Langmuir model. The Langmuir parameters qm ( maximum amount of protein adsorbed, mg BSA/g HA) and K' (affinity constant, mllmg BSA) have been calculated. qm decreased from 119 to 61.3 with the increase in pH from 4.7 to 7.4. A maximum of 46.1 for K' was determined at pH.5.6 and K' had the lowest value of 3.5 at pH.7.4. Electrostatic attractions were held responsible for the K' maximum at pH.5.6 since HA and BSA surfaces are oppositely charged. The presence of a considerably high amount of BSA adsorption on the HA surface at pH.4.7 where the protein should have close to zero net charge was attributed to hydrophobic effects. The amount of adsorption at equilibrium in the 4.5-5.8 pH range was determined to be twice of that in the 6-8 pH range. Almost 100% of the protein was recovered with a HA solids loading of 750 mg HA/50 ml solution at equilibrium for an initial BSA concentration of I mg BSA/ml solution.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 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).