Preparation, Charaterization And Primary Application Of Functionalized Magnetic Polymer Microspheres

Now with the research development in field of biomedicine and bioengineering, people are exploring various functional polymer microspheres which can serve as smart or intelligent tools for drug delivery, biomacromolecules purification, biosensor and enzyme immobilization,etc. Based on the research background and the development trend of polymer microspheres,the research interest of this work focused in the preparation and primary application of functionalized magnetic polymer microspheres, which involves in five parts, i.e. the preparation and surface modification of magnetite nanoparticles, preparation of magnetite@silica particles, preparation and primary application of dual-responsive polymer microspheres which possess magnetically responsive and thermoresponsive properties, and preparation of fluorescence labeled dual-responsive polymer microspheres. The results of each part are listed as follows:(1) Magnetite nanoparticles were prepared by chemical co-precipitation process. Different reaction parameters including reactant concentrate, reactant molar ratio and reaction temperature were found to dramatically influence the properties (particle size, superparamagnetic property, etc). Finally, superparamagnetic magnetite nanoparticles of about 15nm were obtained by using proper reactant concentrate, feeding ratios and controlling the reaction temperature increased stepwisely. The characterization results of vibrating sample magnetometer, X-ray diffraction and transmission electron microscope confirmed superparamagnetic magnetite particles with an average size of about 15nm were prepared.(2) By treating as-prepared magnetite nanoparticles with trisodium citrate aqueous solution, stable magnetic fluid (dispersion of magnetite nanoparticles in water) was prepared. It was found that, to some extent, more amount of trisodium citrate was used to modify the magnetite nanoparticles, more stable magnetic fluid was produced. Using the modified magnetite nanoparticles as seeds, silica-coatedmagnetite particles (magnetite@silica) were prepared via a modified Stober method. It was found that the morphology of resulted magnet ite@si lie a particles is related with the extent of modification of magnetite. When magnetite particles modified with small amount of trisodium citrate were used as seeds, the magnetite@silica particles were silica-coated magnetite clusters, and when magnetite particles modified with larger amount of trisodium citrate were used as seeds, magnetite@silica shows a typical spherical shape and core-shell structure. The size of magnetite@silica particles is dependent of the amount of the precursor(tetraethyl orthosilicate).(3) Using magnetite@silica particle as seed, a dual-responsive polymer microsphere with core-shell structure was prepared by precipitation polymerization. The prepared microsphere consists of magnetite@silica core and crosslinked PNIPAM shell. The core of these microspheres could be tuned by using magnetite@silica particles of different size as seeds, and the crosslinking densities of the PNIPAM shell could be changed by changing the amount of crosslinker in the preparation recipes.The characterization results show that the prepared microspheres possesss magnetic property and thermoresponsive property, and the LCST of the microspheres could be tuned by changing the crosslinking density, when the crosslinking density of PNIPAM shell attained 25%,the LCST of the microsphere increased to 37°C. TEM and SEM observation shows that the size of the microspheres is in range of submicron scale. It is worthy noting that the method used in this study could be extended to prepare other inorganic-core-organic-shell polymer composite microspheres when various inorganic nanoparticles (Au, CdS, nanozeolite, etc.) are used, furthermore, other polymer could also be form on the surface of these inorganic particles through radical polymerization of corresponding monomers.(4)By using the prepared dual-responsive microspheres of different crosslinking densities(15%, 20% and 25%) as carrier of an anti-tumor drug (DOX), it was found that microspheres of higher cosslinking density possess lower drug loading capacity. Increasing the weight ratio between drug and microspheres could increase the drug loading efficiency but decrease the drug entrapment efficiency. All these microspheres showed a restively higher drug loading efficiency at a pH value of about 7. The invitro drug release results showed that the drug release behavior of DOX-microspheres is characteristic with temperature-dependence. At about 37°C, DOX-microspheres show a relatively rapid release of DOX, and the prolonged release time of the drug on the microspheres was found when the cross linking density was increased. Using the DOX-microspheres as medicament, the animal test results showed that under the guidance of applied magnetic field, the DOX-microspheres could efficiently concentrated at the targeted tumor in the body of rats, and compared with pure DOX, the tumor inhibition effect of DOX-microspheres increased significantly, i.e. about five times higher than that of pure DOX. The side-effect of DOX-microspheres was also greatly reduced as a result of controlled release of DOX from microspheres in tumor. Furthermore, although the whole polymer microsphere is not biodegradable and biocompatible, almost no toxicity was found according to pathological test results. The animal test results reveal to us that the dual-responsive microspheres showed great application potential in the design of magnetically targeting drug delivery system for tumor therapy.(5) To further functonalization of dual-responsive polymer microspheres, a fluorescent molecules (fluorescein isothiocyanate, FITC) was incorporated into the silica shell of magnetite@silica, and through a preparation process similar to that for preparation of dual-responsive polymer microspheres, FITC-labeled dual-responsive polymer microspheres were prepared. As was characterized with transmission electron, scanning electron microscopy and atom force microscopy, the submicron sized microspheres showed nearly monodispersed size distribution, core-shell structure and spherical shape. Dynamic light scattering showed the microsphere possess thermoresponsive property, and the characterization results of fluorescence microscopy showed the obtained FITC-labeled dual-responsive microsphere had high luminescent intensity as a result of larger amount of FITC concentrated in the core of the microspheres. The fluorescent emission spectra of FITC, FITC-labeled magnetite@silica particles and FITC-labeled dual-responsive polymer microspheres demonstrated that the FITC molecules were successfully incorporated into the microspheres. Since the microspheres instigated the property of magnetic polymer...