Investigation Of Focusing And Constraining Fe₃O₄ Nanoparticles By Using Permanent Magnets

Fe₃O₄ nanoparticles are superparamagnetic substances with high specific surface area,easy surface modification,good biocompatibility and low toxicity,etc.,which have been widely used in many fields such as biology and physics,especially in the field of biomedicine.Applications of Fe₃O₄ nanoparticles in the field of biomedicine mainly include:magnetic carriers in magnetic drug targeting,magnetic responsive particles in material magnetic separation,contrast agents in magnetic resonance imaging.In most of these applications,magnetic field is used to supply magnetic force on Fe₃O₄ nanoparticles.For example,in magnetic drug targeting,mainly use magnetic field to control the drug-carrying Fe₃O₄ nanoparticles in the body,so that they can gather in the body lesions for targeted therapy and reduce the damage of drugs to normal tissues and cells.The Fe₃O₄ nanoparticles carrying the target material are captured by magnetic field in magnetic separation to separate the target material from the mixture.Apparently,magnetic field occupies an important role in the application of Fe₃O₄ nanoparticles.Of the two major types of magnetic fields:permanent magnetic field and electromagnetic field,the permanent magnetic field has the advantages of economy,safety and convenience compared with the electromagnetic field,so rare earth permanent magnet is a good choice.However,due to the divergence of the magnetic field environment,the current focusing and constraining of Fe₃O₄ nanoparticles by permanent magnets has the disadvantages of low efficiency,poor aggregation effect and low targeting accuracy.Therefore,it is of great significance to study the distribution characteristics of permanent magnetic field,explore the law of permanent magnet on Fe₃O₄ nanoparticles,and design a magnetic field that can efficiently focus and constrain Fe₃O₄ nanoparticles.Firstly,the distribution of magnetic field of ordinary permanent magnets is studied in this thesis.The finite element software ANSYS is used to simulate the magnetic fields of permanent magnets of different shapes and sizes,including single or multiple cylinders,hollow cylinders,rectangular magnets,etc.The difference between the magnetic fields generated by magnets of different shapes and sizes is visually compared from the shape of the magnetic field distribution contour plot.The experimental results found that:In a magnet,the region with the largest magnetic field strength is at the edge of the magnet.The shape and size of magnets have a great influence on the distribution of magnetic field.For example,in cylindrical magnets,the magnetic field intensity on the surface of the magnet increases with the decrease of the aspect ratio.Different arrangement of magnets also has a great impact on the distribution of magnetic field.Through reasonable arrangement of magnets,a higher distribution of magnetic field will be obtained.After studying the characteristics of permanent magnetic field distribution,this thesis systematically classifies the Fe₃O₄ nanoparticles focusing and constraining magnetic field into three types:one-dimensional focusing and constraining magnetic field,two-dimensional focusing and constraining magnetic field,three-dimensional focusing and constraining magnetic field.A plurality of magnet structures capable of focusing and constraining Fe₃O₄ nanoparticles also exemplified,including:Hollow cylindrical permanent,specially arranged three permanent magnets,Halbach array magnets(which capable of achieving one-dimensional focusing);Single permanent magnet,two permanent magnets arranged in different directions(which can realize two-dimensional focusing);And the theoretical conjecture of realizing three-dimensional focusing and constraining.The effects of common permanent magnets on the focusing and constraining of Fe₃O₄ nanoparticles were preliminarily studied.A method for efficient aggregation of Fe₃O₄ nanoparticles using time-varying magnetic field was proposed,and an experimental device was designed and processed.The device is mainly composed of a pair of permanent magnets with N pole and S pole facing each other.The two magnets rotate around the axis between the magnets.The selected axis is perpendicular to the axis of the magnets,and the container containing the suspension solution of Fe₃O₄nanoparticles is fixed at the position of the rotating shaft,when the magnet is not rotating,it can be seen that the particles gathered at the two ends of the container close to the magnet,and when the magnet is rotated,it can be seen that the particles are rapidly gathered.The experimental results show that the Fe₃O₄ nanoparticles can be gathered efficiently under time-varing magnetic field which is not possible under the same condition without rotation,and the aggregation speed and effect are better than those under static field.In addition,this paper also explores the methods to realize three-dimensional focusing and constraining of Fe₃O₄ nanoparticles.Several experiments have been carried out in various magnetic field environments(including time-varying N-S permanent magnet device,time-varying single permanent magnet device,combined with magnetic material,etc.),a hourglass-shaped magnetic field environment also specially designed.By increasing the viscosity of the solution,a brief three-dimensional suspension of the particles is achieved in some magnetic field environment.The experimental results show that there are challenges in achieving three-dimensional focusing and constraining under magnetic field.An effective method to achieve precise targeting is to combine magnetic field with other technologies.