Preparation And Characterization Of Monodisperse Fe₃O₄Magnetic Microspheres With High Magnetic Response

Due to the biocompatibility and nontoxicity, Fe3O4has been widely used in the bio-field. And monodisperse microspheres have attracted great interest recent years because of their wide applications in various fields. Magnetic microspheres allow the controlled release of medicine and targeted drug delivery. However, the Fe3O4nanoparticles used for magnetic microspheres are most prepared by chemical coprecipitation process, which leads to the low saturation magnetization and oxidizable of the samples. By contrast, solvothermal method has become a research hotspot, which brings about the good performance of products, such as monodispersity, high crystalline and high purity. However, solvothermal method process needs to be studied further for smaller particle size and more uniform dispersibility.In this work, a T-shaped microchannel reactor was employed to prepare monodisperse magnetic microspheres. The shell of microspheres were PLA and PLGA, the FDA approved polymer, which are widely used in the field of drug delivery based on its biodegradability and biocompatibility. The essential component of microsphere core was hydrophilic Fe3O4featuring high magnetic responsiveness prepared by using solvothermal. The effects of the emulsion flow rate and the encapsulation temperature on the microsphere shape were discussed in detail for the optimum process parameters. The crystalline property of the Fe3O4was tested using X-ray powder diffraction (XRD), and its magnetic property was measured by vibrating sample magnetometer (VSM). The functional groups of the Fe3O4were characterized by Fourier transform infrared spectroscopy (FT-IR). The content of Fe3O4in the microspheres was confirmed by thermal gravimetric analysis (TGA). The morphology of all samples was observed by scanning electron microscopy (SEM).The main results are summarized as following:(1)The preparation and characterization of Fe3O4nanoparticlesThe effective ingredient of nanoparticle prepared by solvothermal method is hydrophilic FeaO4. The saturation magnetizations of samples prepared by chemical coprecipitation process, water solvothermal method and glycol solvothermal method are57.455emu/g,90.5837emu/g and88.4683emu/g respectively. The Fe3O4prepared by solvothermal method exhibits good hydrophilic.The main influencing factors of solvothermal method process are considered to be precursor’s concentration, reaction temperature and reaction time.(2) The preparation of magnetic microspheres by composite emulsion methodAccording to the optimum process parameters, magnetic microspheres with smooth surface and size distribution of10-50nm can be successfully manufactured. The process parameters are as following:nanoparticle Fe3O4prepared by solvothermal method as core materials, PMMA as shell materials,1wt%PVA solution, m(core):m(shell)=4:1. emulsifying speed for5000r/minDue to the low coating rate, this composite emulsion method is not an ideal approach for preparing magnetic microspheres.(3) The preparation of magnetic microspheres by T-shaped microchannelThe mass fraction of gelatin between0.25wt%to0.5wt%is helpful to form stable W/O/W emulsion. With the flow rate of W/O phase at0.5μL/min and that of additional water phase at150uL/min, the resulting microspheres were entirely spherical in shape with smooth surfaceThe microspheres were obtained by the evaporation of DCM, and the Fe3O4were then embedded in the PLA matrix. In the curing temperature of about20℃, the Fe3O4nanoparticles were evenly dispersed in the microspheres. The microspheres have a uniform particle size of approximately145μm. Hence, the embedding ratio of Fe3O4in PLA microspheres was up to62.7%. Based on the gas chromatography test, the residual concentration for DCM in the magnetic microspheres is less than160ppm. The magnetic microspheres exhibited typical paramagnetic with the saturation magnetization of0.96emug-1.The optimum process conditions are as follows: m(Fe3O4):m(PLA)=1:10,tne flow rate of additional water phase at is150μL/min, the flow rate of W/O phase is0.5μL/min, length of microchannel is5m. The width and depth of microchannel are330μm for oil phase and500μm for additional water phase.