Magneto-caloric Effect Of Iron Oxide Nanoparticles And Their Distribution In Substantia Nigra And Cells

With polyethylene glycol?PEG?as solvent and reactant,polyvinylpyrrolidone?PVP?or polyvinylimide?PEI?as additive,and ferric acetylacetonate?Fe?acac?₃?as iron source,superparamagnetic iron oxide nanoparticles?SPIONs?with good biocompatibility,uniform size and controllable particle size?6?15 nm?were prepared by modified polyol pyrolysis method.The magneto-caloric effect of SPIONs in alternating magnetic field?ACMF?was studied by using SPIONs with different particle sizes.The physicochemical properties of SPIONs surface were adjusted by modifying the surface of SPIONs:1,2-Dimyristoyl-sn-glycero-3-phosphocholine?DMPC?was modified on the surface of PVP/PEG-SPIONs by physical adsorption to prepare DMPC/PVP-SPIONs;streptavidin?SA?was modified on the surface of PEI/PEG-SPIONs by chemical crosslinking to prepare SA/PEI-SPIONs.The expected effect can be achieved when they interact with organisms after modifying the surface of nanoparticles.The main research results are as follows:?1?The particle size of SPIONs was controlled by changing reflux temperature and time,different particle sizes of SPIONs were dispersed in deionized water to obtain different concentrations of dispersions,then magneto-caloric heating experiments were carried out in ACMF with a frequency of 425 kHz and a magnetic field intensity of 5.3kA/m.In this work,the relationship between specific absorption rate?SAR?and particle size of SPIONs was discussed,Brownian relaxation time and Neel relaxation time were calculated.It was found that the heating rate of SPIONs dispersions was proportional to the particle size of SPIONs.The larger the particle size of SPIONs was,the higher the SAR value would be,and the highest SAR value could reach 810 w/g;?2?PVP-SPIONs were prepared by polyol pyrolysis and DMPC/PVP-SPIONs were synthesized thereafter.The characterization results showed that DMPC was successfully modified on PVP-SPIONs.The two kinds of nanoparticle in aqueous dispersions were injected into the substantia nigra of SD rats by stereotaxic injection and the rats brains were taken out after 24 h and 1 week,respectively.The results of transmission electron microscopy?TEM?showed that after 24 h of injection of DMPC/PVP-SPIONs into substantia nigra,the nanoparticles were dispersed in synapses,axon terminals,myelin sheaths,lysosomes and cytoplasm.In the samples injected with PVP-SPIONs,nanoparticles were only found in the cytoplasm or lysosome,while few were found outside the cells.There were few nanoparticles in substantia nigra 1 week after injection of the two kinds of nanoparticles.By detailed analysis using ICP-OES,the amount of DMPC/PVP-SPIONs in substantia nigra was less than that of PVP-SPIONs.This is because that the similar structure of DMPC and cell membrane increases the efficiency of nanoparticles passing through cells and makes it easier to transport in the brain.Therefore,the iron content in substantia nigra is less than that in PVP-SPIONs.On the other hand,PVP-SPIONs and DMPC/PVP-SPIONs were cultured with PC-12 cells respectively.The results showed that DMPC/PVP-SPIONs were easier to enter cells but PVP-SPIONs were less in cells.This can be ascribed to that the phospholipid structure of DMPC makes it easier for nanoparticles to enter cells in vitro;?3?The effective attachment of magnetic nanoparticles on cell membranes plays an important role in the activation of cell membrane TRPV1 channels.Streptavidin?SA?was successfully modified on the surface of PEI-SPIONs to form SA/PEI-SPIONs with high colloidal stability and low cytotoxicity.The results of XPS,UV and FT-IR analysis showed that SA was successfully modified on the surface of PEI-SPIONs.PEI-SPIONs,SA/PEI-SPIONs and PC-12 cells were incubated in RPMI 1640 complete culture medium containing 0.2 mg/L biotin for 12 h.The distribution of nanoparticles in sub-cell structure was observed by TEM after the cells were collected and fixed.The results showed that PEI-SPIONs were mainly distributed in intracellular lysosomes.But SA/PEI-SPIONs were clearly attached to cell membranes,which could be attributed to the specific binding between SA and biotin sites.This work provides a simple way to attach SA-modified nanoparticles to cell membranes by culturing cells in culture medium containing biotin;?4?Fluorescein FITC bound with SA was modified on the surface of PEI-SPIONs.FITC-SA/PEI-SPIONs were stereotaxically injected into the substantia nigra of AVV-DIO-ChR2-mCherry transfected mice.The distribution of nanoparticles in substantia nigra injected with biotin was studied by fluorescence labeling and TEM.The nanoparticles were found around dopaminergic neurons in substantia nigra,indicating that the strong binding force between biotin and SA could improve the efficiency of nanoparticles to attach cell membranes.In this work,nanoparticles have low toxicity and good biocompatibility,and the amount of SA-modified nanoparticles adhering to cell membranes is significantly increased by simply supplying trace biotin to substantia nigra.Therefore the applicability of this method for nanoparticles to adhere cell membranes in vitro or in vivo is verified.