Preliminary Studies On The Negative MRI Contrast Agents Of Amphiphilic Lysine Modified Chitosan

Nowadays, superparamagnetic iron oxide (SPIO) is one of MRI contrast agents which are researched more and more .It is a special MRI contrast agents for reticuloendothelial system. After entering into blood, the SPIO is combined with plasma protein and is swallowed by phagocyte which only exists in normal cells of reticuloendothelial system. As a result, the signals of normal cells are decreasing, but tumor tissues are unchanged. Thus normal cells are distinguished from tumor tissues by MRI. In this paper, we take chitosan as basic material to prepare the micelle and liposome which can encapsulate Fe₃O₄ as a MRI contrast agent by self-assembly method. The detail is as follows:Firstly, the Octadecyl quaternized lysine modified chitosan (OQLCS) was synthesized. In view of polyethylene glycol(PEG) has an advantage on circulation time and folic acid(FA) has the ability of targeting, so the PEG and FA are used which are both biocompatible to modify OQLCS by grafting reaction. It is expected to get an multifunctional OQLCS. The samples were characterized by FT-IR and 1H-NMR. The results showed that we have prepared PEG-OQLCS and FA-OQLCS successfully.Secondly, supermagnetic nanoparticles Fe₃O₄ was prepared by high-temperature solution phase reaction which was characterized by FT-IR,XRD,VSM and so on. Then we utilized lysine modified chitosan to encapsulate Fe₃O₄. Lattics-lattice relaxivities (T2) have been investigated; the results showed that the relaxivity of PEG-OQLCS micelle encapsulating Fe₃O₄ 164.14mM^-1 s^-1 and the PEG-OQLCS and FA-OQLCS mixing polymeric liposomes encapsulating Fe₃O₄. is 160.58 mM^-1 s^-1.To sum up, the study showed that chitosan derivatives and Fe₃O₄ applied in MRI contrast agents is feasible, and this lay the foundation for its further application in the biomedical field.