The Synthesis Of Carbon Nanotubes / Magnetic Nanoparticle Hybrids And Their Applications In Magnetic Resonance Imaging

Carbon nanotubes (CNT) have attracted considerable attention since they were discovered by S. Iijima in 1991, because of their unique optical, electronic, mechanical properties and high surface area, low toxicity and good biocompatibility. To broaden their applications in various areas, many different organic and inorganic nanoparticles or other medical molecules were used to functionalize the CNT. This thesis mainly studied the controlled synthesis, biocompatibility properties, magnetic resonance imaging (MRI) and drug delivery applications of MWCNT/CoFe₂O₄ and MWCNT/Fe₃O₄ hybrids. There are four chapters in this thesis.In chapter 1, The structure and properties of CNT, the way to modify carbon nanotubes with nanoparticles and the biomedical applications of CNT have been summarized. Meanwhile, the correlative theory of MRI and the applications of CNT in MRI are also reviewed. The research envisagement of this thesis is proposed in the end.In chapter 2, the MWCNT/Cs/CoFe₂O₄ nanocomposites were synthesized by a hydrothermal method. The reaction temperature and the charging concentration of metallic salts can influence the morphology of the products. The magnetic properties and the potential applications as MRI contrast agent of the as-prepared materials were also studied. Meanwhile, a solvothermal method was utilized to synthesize MWCNT/CoFe₂O₄ hybrids through high-temperature decomposition of intermediate complexing compounds using DEG and DEA as solvents and complexing agents. The reaction temperature significantly affected the structure of the resultant hybrids. Under optimal conditions, the superparamagnetic MWCNT/CoFe₂O₄-180 hybrids with CoFe₂O₄ nanoparticles uniformly coated on the surface of CNT were synthesized. In vitro experiments revealed that the MWCNT/CoFe₂O₄-180 hybrids displayed low cytotoxicity and neglectable hemolytic activity, and an excellent MRI enhancement effect on cancer cells. In addition, the hybrids showed a high loading capacity for anticancer drug DOX. The good stability of DOX-loaded MWCNT/CoFe₂O₄-180 in normal physiological buffer and fast drug release in acidic environments are ideal properties for in vivo drug carriers. Importantly, the DOX-loaded hybrids exhibited notable cytotoxicity to HeLa cells. Therefore, MWCNT/CoFe₂O₄-180 hybrids have great potential to be used as effective MRI contrast agents and drug carriers for diagnostic and therapic applications.In chapter 3, the MWCNT/Fe₃O₄ hybrids were synthesized by an in situ solvothermal method using DEG and DEA as solvents and complexing agents. The resultant superparamagnetic MWCNT/Fe₃O₄ hybrids displayed highly hydrophilic property, low cytotoxicity, neglectable hemolytic activity, and a significant MRI negative contrast enhancement effect on cancer cells. In vivo MRI studies showed that the T₂-weighted MRI signal in the liver and spleen of mice decreased significantly after intravenous administration, suggesting the potential application of the hybrids for MRI contrast agents. Moreover, an intensive exploration about the in vivo behavior of the MWCNT/Fe₃O₄ hybrids was carried out by the organ biodistribution studies, histological analysis and elimination investigations. These results demonstrate that the MWCNT/Fe₃O₄ hybrids would be uptaken by the liver, lung and spleen after intravenous administration, and can be excreted from the elimination organs of liver and kidneys. Findings from this work have provided some basic information on the biocompatibility of magnetic nanoparticle coated CNT which is beneficial for their future biomedical applications.In chapter 4, the important results obtained in this work are summarized, and the application prospects of the prepared materials in the biomedical fields are also mentioned.