Thesis (Ph.D.) - University of St Andrews, February 2008.

Thesis (Ph. D.)--University of Washington, 2005. / Vita. Includes bibliographical references (leaves 168-171).

No description available.

In this thesis, a rapid magnetic printing technique has been developed for contactless, label-free, and scaffold-free printing of three dimensional (3D) cellular structures in vitro. The biological inks (bioinks) used to form these structures were composed of cells suspended in a liquid medium. Development of this technique was based on exploiting the inherent magnetic susceptibility of cells. Since cells and their liquid medium are diamagnetic (negative magnetic susceptibility), a paramagnetic salt hydrate, gadopentatic acid (Gd-DTPA), was added to the liquid medium to increase its magnetic susceptibility. When a magnetic field was applied, the host fluid containing the paramagnetic salt was towards regions of high magnetic field strength, displacing the cells towards regions towards regions of low magnetic field strength. This rapid printing technique using magnetic cell bioinks was first described using whole blood to form various structures including spherical clusters (spheroids), strips, and three-pointed stars. This demonstration verified the printing technique as a safe and non-toxic method. Subsequent studies were performed using a frequently studied human breast cancer cell line, Michigan Cancer Foundation-7 (MCF-7), to develop a thorough protocol using mammalian cells. Here, the printing method was used to form 3D cellular structures on ultra-low attachment (ULA) and 2.5D cellular structures on tissue-culture-treated (TCT) surfaces. These geometries were produced within 6 hours with high reproducibility. The use of a co-culture on TCT surfaces using MCF-7 and human umbilical vein endothelial cells (HUVECs) and on ULA surfaces using MD Anderson metastatic breast-231 (MDA-MB-231) and embryonic mouse fibroblast (3T3) cells demonstrated the observance of unique cellular interactions and improved printing abilities (accelerated time and improved reproducibly) of the structures printed with magnetic inks, respectively. The use of magnetic cell inks in research and clinical settings can accelerate the development of medical innovations such as drug discovery, personalized medicine, and treatment of disease. / Thesis / Doctor of Philosophy (PhD) / In this thesis, a rapid magnetic printing technique has been developed for contactless, label-free, and scaffold-free printing of three dimensional (3D) cellular structures in vitro. The biological inks (bioinks) used to form these structures were composed of cells suspended in a liquid medium. Development of this technique was based on exploiting the inherent magnetic susceptibility of cells. Since cells and their liquid medium are diamagnetic (negative magnetic susceptibility), a paramagnetic salt hydrate, gadopentatic acid (Gd-DTPA), was added to the liquid medium to increase its magnetic susceptibility. When a magnetic field was applied, the host fluid containing the paramagnetic salt was towards regions of high magnetic field strength, displacing the cells towards regions towards regions of low magnetic field strength. This rapid printing technique using magnetic cell bioinks was first described using whole blood to form various structures including spherical clusters (spheroids), strips, and three-pointed stars. This demonstration verified the printing technique as a safe and non-toxic method. Subsequent studies were performed using a frequently studied human breast cancer cell line, Michigan Cancer Foundation-7 (MCF-7), to develop a thorough protocol using mammalian cells. Here, the printing method was used to form 3D cellular structures on ultra-low attachment (ULA) and 2.5D cellular structures on tissue-culture-treated (TCT) surfaces. These geometries were produced within 6 hours with high reproducibility. The use of a co-culture on TCT surfaces using MCF-7 and human umbilical vein endothelial cells (HUVECs) and on ULA surfaces using MD Anderson metastatic breast-231 (MDA-MB-231) and embryonic mouse fibroblast (3T3) cells demonstrated the observance of unique cellular interactions and improved printing abilities (accelerated time and improved reproducibly) of the structures printed with magnetic inks, respectively. The use of magnetic cell inks in research and clinical settings can accelerate the development of medical innovations such as drug discovery, personalized medicine, and treatment of disease.

A study was conducted to investigate the effect of magnetic devices on the precipitates in a condenser’s tubes when seawater is used as cooling water. This test was necessary to evaluate these devices as possible replacements for conventional methods of water treatment. In the test program, a small condenser was operated with conditions similar to utility condensers. This condenser was modified to include twelve tubes. The inlet water box was divided to provide for two parallel magnetic water treatment streams, and one control untreated water stream for comparison purposes. With and without the use of a magnetic device, the chemical analysis and the thickness of the deposits showed no significant difference. The only difference that was observed in these deposits was their crystallogical structure. When the magnetic device was in place, deposits were flaky (powder-like), chipped, and showed no strong adhesion to the inner surface of the condenser’s tubes. Without the use of a magnetic device, deposits were flocculated, hard, and crusty. This thesis proposes a theory which may help explain the differences in the deposits. The theory will include homogenous nucleation to explain the physical changes of the deposits. The discussion will also postulate how well the magnetic energy improved the homogenous nucleation process. A method of analysis is proposed which demonstrates how the critical radius of a nucleus is affected by a magnetic field.

We present a study on perpendicular magnetic tunnel junctions with W as buffer and capping layers. A tunneling magnetoresistance of 138% and an interfacial magnetic anisotropy of 1.67 erg/cm(2) were obtained in optimally annealed samples. However, after extended annealing at 420 degrees C, junctions with W layers showed extremely small resistance due to interdiffusion of W into the MgO barrier. In contrast, in Ta-based junctions, the MgO barrier remained structurally stable despite disappearance of magnetoresistance after extended annealing due to loss of perpendicular magnetic anisotropy. Compared with conventional tunnel junctions with in-plane magnetic anisotropy, the evolution of tunneling conductance suggests that the relatively low magnetoresistance in perpendicular tunnel junctions is related to the lack of highly polarized Delta(1) conducting channel developed in the initial stage of annealing. Published by AIP Publishing.

Systems of magnetic nanowires are considered strong candidates in many technological applications as microwave filters, sensors or devices for data storage. Because of their strong potential as candidates in such applications they became lately the object of many studies. However, due to the very complicated nature of the interwire interactions, their magnetic behavior is very difficult to be interpreted. The main parameter controlling the response of magnetic nanowires assemblies is the aspect ratio of the nanowires that is defined as the ratio of the length to the wire's diameter. In our study we choose to modify the aspect ratio by keeping a constant length of nanowires and modifying the wire's diameter while keeping the same interwire distance. The samples were studied at room temperature, using vibrating sample magnetometer and X-band ferromagnetic resonance experiments. The results are explained taking into account the effects of the magnetostatic interactions and shape anisotropy.

Thesis (Ph. D.)--University of California, San Diego, 2003. / Vita. Includes bibliographical references.

No description available.

No description available.