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Medical applications of calcium phosphate biomaterials are limited because of poor mechanical properties and acute inflammation reactions which take place occasionally in the clinic. To increase the usefulness of calcium phosphate biomaterials it is necessary to improve the mechanical properties and biological character. Processing and characterization of porous hydroxyapatite (HA) and dense composite (HA-Spinel) biomaterials have been performed in the present research. Biocompatibility of these biomaterials has been examined in vitro using human and rat immortalized osteoblast cells, and the advantages and limitations of cell culture biocompatibility tests are discussed. X-ray analysis of material structure demonstrated that after sintering at 1450°C, HA-Spinel was changed into tricalcium phosphate (TCP)-Spinel phase structure. Mechanical properties testing showed that the bending strength and compressive strength of HA may be improved by adding Spinel. Biocompatibility examination demonstrated that both human and rat osteoblast cells anchored to the surface of the porous and dense biomaterials in a short time, and subsequently, grew and proliferated normally on the surface of these biomaterials. Cytotoxicity evaluation in vitro by studying material extracts demonstrated that compared with the control group of cells cultured on polystyrene, HA-Spinel possessed slight toxicity. Cell growth in HA-Spinel first extracts was slightly impaired. Tritium labeling and immunofluorescent analysis proved that human osteoblast cells and rat osteoblast cells have normal expression of collagen synthesis on the above biomaterials. Confocal laser scanning microscopy (CLSM) observation showed that collagen fibers were produced on these materials, and the amount of the collagen synthesized on the materials increased with culture time. Subsequent analysis indicated that both HA and HA-Spinel can strongly adsorb serum and albumin proteins from culture media and the amount of protein adsorption was proportional to the porosity in the materials. Protein adsorption on the material surface was saturated usually in 2-4 hours, and 1/3-1/2 of the total protein adsorption was achieved in several minutes. In vitro assay also confirmed that human and rat osteoblast cells can be applied as an in vitro model to evaluate the biocompatibility, cytotoxicity and other biological characteristics. Compared with human osteoblast cells, rat osteoblast cells have a greater proliferation rate. In normal conditions, the proliferation rate of the rat osteoblast cells is 2-4 times that of the human osteoblast cells and for this reason rat osteoblasts seem more sensitive to material extracts.

The spinel structure of LiMn2O4 powders react with the 1 mole Li2CO3 and 4 mole MnO2 powders by solid-state reaction at 800 oC, and then sintered at 1300 oC to become ceramics specimen. There are accompany phase transformation and non-stoichiometric composition during the cooling process. In X-ray diffraction analysis, the sintered specimen contains principal Li-deficiency Li1-XMn2O4 composition and minor of second phases LiMnO2 and Mn3O4. Lattice parameters also distorted by John-Teller effect. In electron microscopy observation, there are lamellae grains and defects in the specimen, such as twins, dislocations and stacking faults. In TEM analysis, tetragonal-LiMn2O4 structure has lamellae domains, and reflection twinning. However, this study for cubic-LiMn2O4 structure found that edge dislocations with Burger vector of 1/2<110> slip on {110} plane, and mixed(45o) dislocation with Burger vector of 1/2<100> slip on {100} plane.

Multiferroic materials, showing strong coupling between ferroelectric and ferromagnetic interaction, have been the subject of intense research recently. These materials are potential candidates for the next generation in microelectronic device. CdCr2S4, one of the few multiferroics with spinel structure proposed in 2005, is in the limelight of scientific research, because of the complex interaction among lattice, spin and dipole. To investigate further, we have measured the magnetic and electric properties of single crystal CdCr2S4. The spins are coupled ferromagnetically below Curie temperature TC = 84 K. With increasing magnetic field, ferromagnetic transition is found to be shifted towards higher temperature. The magnetic hysteresis is satisfied with the characteristic of soft ferromagnet. Electric field induced permanent metal-insulator transition (MIT) and colossal magnetoresistance (CMR) are observed in the resistivity measurement. From dielectric constant measurement, two interesting dipolar ordering states have been observed. The peak near TC ~ 84 K is due to the glassy type dipolar state stimulated by the onset of ferromagnetic ordering and the other near 54 K, might be the ferroelectric ordered state induced by externally applied electric field. Both electric and magnetic field dependent physical properties have been studied and reveal significant evidences of strong spin-dipole coupling in the present system.

Thesis (M.S.)--West Virginia University, 2003. / Title from document title page. Document formatted into pages; contains viii, 53 p. : ill. (some col.) Includes abstract. Includes bibliographical references (p. 51-53).

Thesis (Master)--İzmir Institute of Technology, İzmir, 2004. / Includes bibliographical references (leaves.53-56).

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