Phd Degree / Doktora

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  • Doctoral Thesis
    Dynamic Wear Simulations of Hip Implants for Daily Life Activities
    (01. Izmir Institute of Technology, 2024) Alpkaya, Alican Tuncay; Mihçin, Şenay
    Total hip replacement is widely used around the world for patients whose hip joints lost their functionality. Despite its wide applications and technological developments taking place in the recent years, it still does not produce near-perfect results. It has been observed that many patients with implants have their range of motion often restricted. Although there has been literature covering the daily life motion profiles in Western societies, , it has been observed that a through database of activities including sitting, worship, and lifestyles suitable for Middle Eastern societies is non-existent.Therefore, it is difficult to determine the lifespan of implants used especially in these societies and to determine their wear rates with accuracy. In this thesis, I have utilized the first comprehensive database of daily activities of Turkish population, which was formed using the state-of-the-art motion capture (MOCAP) technologies at Biomechanics and Motion Capture Laboratory of IZTECH. The range of motion and reaction force data were calculated using the inverse kinematics and kinetics methods previously. This previously calculated boundary conditions are fed into the finite element models of hip implants to simulate ten distinct daily life activities Asian style sitting, normal walking cycle, obstacle crossing, Stoop lifting, Squat lifting, Ruku' and I'tıdal, Ruku to Sujud, Sujud, Ascending stairs, and Descending Stairs. The dynamic simulations of hip implants under these boundary conditions are performed in this thesis. In this thesis, a computational wear methodology is utilized to assess the wear performance of hip bearing surfaces under these boundary conditions. Each comprehensive computational wear simulations of each of these daily life activities over five million cycles is performed to provide omputational evidence on the wear rates to assess the wear performance of the bearing couple. The wear prediction model could be utilized to provide guidance on the design parameters with the aim of prolonging the life span of hip implants.
  • Doctoral Thesis
    Preparation and Characterization of Resorbable Calcium Phosphate Based Bioceramics
    (Izmir Institute of Technology, 2010) Çetin, Ali Emrah; Çiftçioğlu, Muhsin; Çiftçioğlu, Muhsin
    The main objective of this study was to determine the behavior of hydroxyapatite powders in solutions containing major ions found in human blood plasma. Research efforts however were focused on two different fields, chemical analysis and dissolution testing of hydroxyapatite. Arsenazo III-calcium analysis method was selected and modified for the low level calcium analysis whereas malachite green phosphate assay was used for phosphate determinations. Arsenazo III reagents with different dye concentrations and pH values were tested for the analysis of low levels of calcium. The effects of ions at their blood plasma concentration levels on the modified calcium analysis method were further evaluated. Effects of these ions on the accuracy of phosphate analysis by malachite green assay were also investigated. Dissolution behavior of synthesized and commercial hydroxyapatite was investigated by immersing pellets in several solutions. Calcium and phosphate release kinetics in ultrapure water, sodium chloride and sodium bicarbonate solutions were investigated. Commercial hydroxyapatite pellets were also immersed separately in magnesium chloride, and sodium chloride/bicarbonate solutions. Calcium concentrations in solutions were found to decrease in the following order: sodium chloride > ultrapure water > bicarbonate. Phosphate concentrations in solutions were found to follow an order of sodium bicarbonate > sodium chloride > ultrapure water. Bicarbonate-phosphate ion exchange was observed in bicarbonate ion containing solutions. Magnesium-calcium ion exchange and adsorption of phosphates on hydroxyapatite surfaces were found to be effective in magnesium ion containing solution.