Measurement Of The Magnetic Moment Of Living Cells Based On Dynamic Image Analysis

The magnetic moment is one of the most important magnetic parameters of magnetic materials.The magnetic moments of magnetic nanoparticle can be distinguished as single particle magnetic moments and multi-particle aggregated magnetic moments.The magnetic moment of a single particle depends on the specific material,particle size,particle surface,the internal structure of the particle and the temperature;the magnetic moment of multiple particles must also take into account the particle size distribution and aggregation state.In cell therapy technology,magnetic nanoparticles are commonly used to label cells and enable cell tracing in vivo to study the in vivo processes and actions of the cells of interest.To more accurately assess the efficiency of labelling live cells with magnetic materials for better in vivo tracing of magnetic nanoparticle-labelled cells,the magnetic moment of live cells labelled with magnetic nanomaterials(magnetic viable cells)needs to be measured.The target motion is measured by external magnetic field induction,and its motion trajectory is recorded using video images.Its motion trajectory is recorded and the motion parameters are obtained by video image processing.The magnetic moment can be calculated by force analysis of the measurement target.Based on this principle,this thesis builds a measurement system to measure and analyze the magnetic moments of magnetic nanoparticles and living magnetic cells.The main work of this thesis includes the following aspects.Firstly,a system was built to measure the magnetic moment of magnetic nanoparticles under aqueous solution conditions.Since the density of Magnetic nanoparticle droplets in aqueous solution is greater than that of their surrounding medium(paraffin),magnetic nanoparticle droplets are subject to gravity and sink rapidly during motion.The gravity must be take into account for measuring their magnetic moments.When designing the magnetic moment measurement system for magnetic nanoparticle labelled cells,on one hand,the gravity and buoyancy can be approximately canceled out because the density of the cells is close to that of the surrounding medium(phosphate buffer),which means the gravity and buoyancy in the vertical direction can be neglected.On the other hand,since the overall magnetic responsiveness of magnetic nanoparticles after labelling cells is much smaller than that of magnetic nanoparticles or their original aqueous solutions,a magnetic field with a larger gradient needs to be designed to induce the motion of the measure target.In order to observe and record the magnetic cell motion,the overall measurement system also needs to be equipped with a microscope.Therefore,a vertical magnetic moment measurement system for measuring the magnetic moment of magnetic nanoparticles and a horizontal magnetic moment measurement system for measuring the magnetic moment of magnetic nanoparticle-labeled cells were designed.1.Design and implementation of a vertical measurement system for measuring the magnetic moment of magnetic nanoparticlesA vertical measurement system based on image processing to analyze the material motion process and calculate the magnetic moment of the material,hereinafter referred to as the vertical measurement system,was designed.Mainly includes: the gradient magnetic field to drive the motion of magnetic materials,the observation system to record the motion of magnetic nanoparticle colloid droplets,and the algorithm for image processing and magnetic moment calculation.The effective area with the most optimum measurement reference value was determined by analyzing three factors: the acceleration curve of the measurement sample,the magnetic induction intensity variation curve and the kinetic energy loss near the bottom.The magnetic moments of magnetic nanoparticles of different concentrations and volumes were also measured to test this perpendicular measurement system.2.Measuring the magnetic moment of magnetic nanoparticles and analyze the resultsThe magnetic moments of magnetic nanoparticles were measured using a vertical measurement system.For the stable state magnetic nanoparticles,the results have a high linear correlation with the VSM and the error of the results is at the level of 10-6 Am2/g.When the material is in an unstable aggregated state,the results are more different from the VSM measurements,but are consistent with the results of the MRI relaxation time and the temperature curve of the material.We give a theoretical explanation in terms of the relaxation mechanism and temperature rise mechanism of the material,when the relaxation time of the material is mainly affected by Brown relaxation,and the VSM shakes the sample during the measurement process to change its unstable aggregation state thus affecting the magnetic moment measurement results.In addition,the magnetic moments of magnetic microspheres and a large number of magnetic erythrocytes were measured,indicating that the system can be used for the measurement of magnetic moments of other magnetic materials.3.Design and implementation of a horizontal measurement system for measuring the magnetic moments of living cells labelled with magnetic nanoparticlesA horizontal measurement system based on image processing to analyze the magnetic cell motion process to calculate the magnetic moment of the material,hereinafter referred to as the horizontal system,was designed.The gradient magnetic field for driving the magnetic cell motion,the observation system for recording the magnetic cell motion,and the algorithm for image processing and magnetic moment calculation were mainly designed.The system is tested with micron-sized magnetic microspheres close to the cell size,and the measurement results of this system have a high linear correlation with the SQUID measurements with an error at the level of 10-8 Am2.After mixing microspheres with different magnetic moments in a certain ratio,the magnetic moments were measured and the ratios were counted using this horizontal measurement system,and the results obtained were in accordance with the pre-mixed ratios,further validating the measurement system.4.Measurement of magnetic moments of magnetic nanoparticles labelled MSCsThe magnetic moments of magnetic nanoparticle labelled MSCs were measured using a horizontal measurement system,and the linear correlation between the measurement results and the iron content measured by inductively coupled plasma mass spectrometry was calculated.The results show that the measurement system can quantify the magnetic moments of individual living cells.