Research On Dynamic Characteristics And Separation Behaviour Of Magnetic Particles In Microfluidic Magnetophoresis System

With the advancement of micro-electromechanical system and micro/nano technology,bio-separation technology based on microfluidic chip system is an important biological separation method developed in recent years.At microscale,effective separation of biological targets is generally achieved by applying different force fields(electric field force,magnetic field force,acoustic standing wave force and optical force,etc.)together with the hydrodynamic force.Magnetophoretic separation technology that realizes fine separation by inducing the movement of magnetic particles by magnetic force has strong controllability and flexibility.The separation efficiency is not affected by surface charge,solution p H value and ionic strength,etc.It has shown broad prospect in biological separation such as cell separation and purification.In the study of magnetophoresis separation,besides the magnetic field force and the viscous resistance force of the fluid,the movement of particles are also affected by particle-particle magnetic interaction and particle-fluid hydrodynamic interaction.Meanwhile in the existing research,the single mode and the poor controllability of magnetic field force give rise to the magnetic agglomeration behavior between the particles.The system can only achieve separation with high precision and resolution at lower particle concentration,limiting its application and further development.Therefore,a systematic study on the dynamic characteristics and separation behavior of magnetic particles in magnetophoresis separation was carried out in this paper with the help of numerical simulation method.According to different magnetic separation conditions,one-way particle-fluid coupling model,two-way particle-fluid coupling model and a direct numerical fully coupled model were constructed,respectively.The effects of magnet structure,particle-fluid hydrodynamic interaction and magnetic agglomeration behavior on the motion characteristics and separation behavior of magnetophoretic particles were explored.This work provided theoretical basis and technical support for the establishment and improvement of high-efficiency magnetophoresis separation system.Firstly,a one-way particle-fluid coupling model(magnetic field coupled with flow field)under low-concentration magnetophoresis separation mode was constructed.The influence law and mechanism of magnet structures,flow conditions and channel structures on separation efficiency of single sized particle and separation precision of double sized particles in the Y-channel magnetophoresis separation system were analyzed and explored.Specifically,by comparing and analyzing the force and capture efficiency of particles under the action of a single permanent magnet and different combined magnets,the influence mechanism of magnetic field spatial distribution on the motion behavior of the particles was clarified,and the optimal arrangement of the magnets was realized.By altering the flow speed ratio of the double inlet and widening the outlet channel,continuous magnetophoresis separation precision of double sized particles was improved.The effective separation of magnetic particles(diameter 4 ?m and 5 ?m)with small size difference was realized.Secondly,a two-way particle-fluid coupling model(magnetic field,flow field coupled with concentration field)under high-concentration magnetophoresis separation mode was constructed.The effect of particle-fluid hydrodynamic interaction on the separation efficiency of magnetic particles in magnetophoresis system was analyzed and explored.Specifically,the potential effects of particle-fluid hydrodynamic interaction on flow velocity and particle dynamics behavior under high concentration conditions were fully considered by introducing magnetic volume force into the flow field.On this basis,the separation efficiency in Y-type channel and straight channel at different initial magnetic particle concentrations were compared and analyzed.The influence mechanism of particle-fluid hydrodynamic interaction on the separation efficiency of the two types of channel was clarified,using the particle flow velocity and dynamic concentration as analytical parameters.Finally,based on arbitrary Lagrangian-Eulerian method and stress tensor method,a direct numerical model of magnetic particles under the action of uniform/gradient magnetic field coupled with flow field was constructed,which solved the coupling problem between particle-particle interaction and particle-fluid hydrodynamic interaction.The agglomeration and separation characteristics of magnetic particles under static/dynamic magnetic field conditions were explored by applying this method.The simulation results show that under static magnetic field,the magnetic particles will agglomerate due to the magnetic interaction force,which makes it impossible to achieve effective separation of multiple targets according to different physical properties of the particles.By adopting the proposed alternating gradient magnetic field driving method,the magnetic force between the magnetic particles changed from attraction to alternating attraction-repulsive mode,thereby effectively suppressing the aggregation behavior of the particles during the separation process,and making it possible to realize high-precision separation of multi-sized magnetic particles.