Preparation And Stability Of Biocompatible Magnetic Fluids

Magnetic fluid （MF）, which has fluidity and presents magnetic interaction onlyunder an external magnetic field, is a novel functional material. Applications ofbiocompatible MFs in biomedical fields, such as magnetic separation, drug delivery,magnetic resonance image and magnetic fluid hyperthermia, have been the hotspot inthe research area of nanomaterial and biological technology. Therefore, the stability ofbiocompatible MFs is vital and crucial for their biomedical applications. In this study,MFs consisting of magnetic nanoparticles which are coated by two kinds of surfactantmolecules （citrate and dextran） were prepared, and their stability and biocompatibilitywere also investigated.Superparamagnetic Fe₃O₄ （magnetite） nanoparticles were firstly synthesized byalkaline coprecipitation of FeSO₄ and FeCl₃ salts, and thenγ-Fe₂O₃ （maghemite）nanoparticles were prepared through oxidizing magnetite nanoparticles using ferricnitrate after acidifing with HNO₃ solution. At last, the maghemite nanoparticles werecoated by citrate or Dextran T-40 and dispersed into aqueous solutions to obtainbiocompatible MFs. The measurements for the zeta potentials of magneticnanoparticles in suspensions at different pH show that the isoelectric points ofmaghemite coated by citrate and dextran T-40 are about 2.6, 5.2 respectively, but theisoelectric point of pure maghemite is 7.4. Thus, maghemite nanoparticles coated bythese two suffactants can be dispersed in physiological solutions with pH=7.0 andcould be used in biomedical research. Also, the stability time of MFs decreases withincreasing external magnetic field. The results of the effect of ionic strength on MFsshow that at the same pH, with increasing the concentration of NaCl solution from0.05 mol/L to 0.3 mol/L, the stability time of MF is getting longer. Fe₃O₄ particles were prepared by chemical co-precipitation method, oxidationprecipitation method and the hydrolysis of FeCl₃ solution.β-FeO（OH） （akageneite-Q）with sheaf structures was prepared via the hydrolysis of 1 mol/L FeCl₃ solution, afterβ-FeO（OH） was reduced and calcined in H₂, Fe₃O₄ particles were obtained. And anovel Fe₈（OOH）₁₆Cl_1.3 nanospindles that form flower-like microstructures wereprepared by the hydrolysis of 2 mol/L FeCl₃ solutions without any additives, puremagnetite （Fe₃O₄） particles were obtained from calcinating Fe₈（OOH）₁₆Cl_1.3 at 630℃in N₂ atmosphere. Compared with the hydrolysis of FeCl₃ solution and oxidationprecipitation, the average size of Fe₃O₄ prepared by co-precipitation method isrelatively monodisperse.MFs consisting of citrate and dextran T-40-coated magnetite nanoparticles wereprepared by co-precipitating Fe²⁺ and Fe³⁺ salts with suffactant solutions throughadding NH₃·H₂O. The measurements for the zeta potentials of magnetic particles insuspensions at different pH show that the isoelectric points of magnetite coated bycitrate and dextran T-40 are about 2.35, 5.85 respectively, whereas the isoelectric pointof pure magnetite is 6.7. These results display that magnetite nanoparticles can bedispersed in physiological environment of pH=7.0 and could be used in biomedicalresearch. The stability time of magnetite coated by citrate with external magnetic fieldunder 500 G and above 900 G is shorter than that of magnetite coated by dextran T-40,when the magnetic strength is between 500 G and 900 G, the stability time of MFsconsisting of citrate-coated magnetite is the same as that of dextran T-40-coatedmagnetite. The results of the effect of ionic strength of NaCl solution on MFs showthat the stability time of MFs is shortest at pH=5.00, and the stability time is longestwhen pH=7.03, hence, MFs consisting of citrate and dextran T-40-coated magnetitenanoparticles could be used in biomedical research.（4） Antibacterium circle experiments and shaking tests primarily confirm that MFsare biocompatible and the stability of MFs is also influenced by colon bacillus.