Magnetothermal Labeling Of Stem Cell For MRI Tracking In Vivo

Stem cell therapy as one of the most promising methods for curing major human diseases,has attracted wide attention from researchers.A clear understanding of the survival,migration and differentiation behavior of transplanted stem cells in the host is an important prerequisite for guiding the efficient treatment of stem cells^[1].Efficient in vivo cell tracing technology that can monitor and quantify the transplanted stem cells in a non-invasive and real-time manner is essential for evaluating the therapeutic effect of stem cells.In this thesis,a new and efficient magnetothermally induced stem cell labeling technology is designed,in which high MRI sensitive vortex-domain magnetic nanorings??-FVIO?with excellent magnetocaloric conversion efficiency under an external alternating magnetic field?AMF?were used as contrast agent,to label stem cells through the magnetic heat under AMF.We systematically carried out the study of cell cytotoxicity,in vitro and in vivo MRI imaging sensitivity,and in vivo long-term cell tracing.The main research content of this paper is divided into the following parts:?1?Ferrimagnetic vortex-domain magnetic nanorings with chemical composition of?-Fe₂O₃ were synthesized by hydrothermal method and thermotropic phase transition.The ligand exchange reaction was used to modify the surface to obtain biocompatible?-FVIO nanoprobe.The results show that the synthesized nanorings have uniform size,and good stability in the aqueous solvent.The specific absorption rate?SAR?of?-FVIO is about 18.8 times than that of superparamagnetic iron oxides?SPIOs?.And its r₂*relaxation rate is about 10 times than that of SPIOs.?2?We further explored the optimal conditions for magnetothermal labeling of stem cell.We determined the optimal labelling concentration of the nanoagent to be 50?g Fe/m L through the cytotoxicity experiment.By applying AMF at different time of the coculture of?-FVIO with stem cells,the cytotoxicity of the cells were analyzed.The optimal application time of AMF was determined to be 1.5 h of the incubation.By applying different time of AMF to the stem cells under labelling,the cytotoxicity and cell uptake were investigated.And the optimal duration of applied AMF is 10 min.The results show that the labeling efficiency of this labeling method is 3.44 times higher than that of ordinary endocytosis labeling while ensure biosecurity.?3?The potential mechanism of magnetothermal labelling a were further investigated.The changes in fluorescence intensity were used to study the temperature changes in the cells membrane during the magnetothermal labeling process,and the possible entry pathways of the?-FVIOs were analyzed.The intracellular distribution of?-FVIOs after labeling were analyzed.The results show that the?-FVIOs quickly heated the cell membrane when the AMF was applied,and then get into cytoplasm.The co-localization efficiency of the?-FVIOs and lysosome in the stem cells was reduced to 37%after magnetothermal labeling,showing that most?-FVIOs were dispersed in the cytoplasm.?4?In vitro MRI studies of labeled stem cells were conducted.MRI was performed magnetothermal labeled stem cells.The relationship between intracellular iron content and signal-to-noise?SNR?ratio were further analyzed.Intracellular iron content changes over time was also studied.The results showed that when the iron content of a single cell is higher than 20 pg,MR r₂*signal of single cell can be detected.After up to 12days culture,the iron content in the magnetothermal labeled stem cells was 37 pg and still higher than 20 pg,indicating that this labeling method allows the contrast agent to stay in the stem cell for a long time and enables long-term tracing.?5?In vivo imaging sensitivity and long-term tracing study of stem cells after magnetothermal labelling were carried out.Stem cells were labeled and transplanted into rat brain in different amounts,for MRI scanning to explore the minimum number of transplanted cells that could be detected.The labeled stem cells were further transplanted into rats for 10 weeks of MRI tracking,to explore the long-term tracing effect.The results show that at least 10 transplanted stem cells can be detected in vivo,and at least 1000 cells can be efficient monitored for long term,which demonstrated that high-sensitivity and long-term in vivo tracking of small-volume transplanted cells is achieved.