Particle Separation Inside Microfluidics Driven By Surface Acoustic Waves

The separation of biological particles plays an essential role in the fields of disease diagnosis,cell research,and drug development.Traditional separation methods such as centrifugation,flow cytometry,and selective precipitation generally have problems such as large equipment volume,many separation steps,large sample consumption,and lengthy procedures.The microfluidic particle separation technology based on surface acoustic waves(SAW)can separate biological particles through a small acoustofluidic chip.It has the characteristics of non-contact,no label and high resolution,and it has significant potential in clinical medical applications.In recent years,the problem of device failure and performance degradation of surface acoustic wave devices due to unfavourable temperature gradients has been raised,but there are few related research results,and there is a lack of heat dissipation packaging structure design for SAW devices.In the study of microfluidics driven by standing SAW(SSAW),the separation mechanism of open micro-droplets is still unclear,and the evaluation of the influence of input parameters on particle separation is ambiguous.Enclosed microfluidics lack in-depth theoretical research on acoustophoresis and methods of improving separation efficiency and purity.Cell separation is still in the scientific research stage,and the separation research of lung cancer cells(non-small cell lung cancer cells)and immune cells(peripheral blood mononuclear cells)has not been carried out.First,the fabrication process of surface acoustic wave devices is systematically studied.Considering the electromechanical coupling coefficient,temperature coefficient and propagation loss comprehensively,the appropriate piezoelectric substrate material is selected,the interdigital transducer structure is designed,and the SAW device is fabricated.A stacking packaging structure using nano-silver adhesive is proposed for the open micro-droplet particle separation device.The thermodynamic model of the structure was established,the thermal conductivity was analyzed and the packaging process was designed.A package structure evaluation criterion for acoustofluidic separation devices is developed.Appearance non-destructive testing,vibration characteristic testing,package strength testing,infrared imaging testing,and impedance characteristic testing were carried out to verify the heat dissipation performance and reliability of the package structure.The stacking package structure addresses performance degradation and device failure issues caused by negative temperature gradients.The particle separation mechanism of open microdroplets and the influence of characteristic parameters were studied.Based on the acoustic streaming theory,the acoustic streaming volume force of the interaction between the acoustic field and the fluid is deduced.Based on the acoustic radiation force theory,the acoustic radiation force of the interaction between the acoustic field and the particles is deduced.An open microdroplet particle separation experimental system and test platform were built.The particle motion behaviour when the contact angle of the droplet changes dynamically was observed,and two-particle motion modes,particle ring and particle disk,were obtained during the separation process.The dominant conversion mechanism of acoustic radiation force and viscous resistance is established.The dimensionless parameter κ quantifies the critical condition that the acoustic radiation force dominates the particle motion.The effects of acoustic frequency,RF input power and particle size on the change of droplet contact angle were quantified by experiments.According to the experimental results,the influence of droplet contact angle on particle separation was further analyzed.The effect of acoustic wave frequency on particle separation was explored,and the mechanism of particle motion and particle separation was revealed.The acoustophoretic motion mechanism and particle deflection characteristics of enclosed microfluidics were studied.The fabrication process of the microchannel and its bonding method with the SAW device were systematically investigated.Based on the governing equation of the fluid,the impedance boundary condition and the particle kinematics equation driven by the acoustics,an enclosed microfluidic particle acoustophoretic motion model driven by the SSAW is constructed.The particle acoustophoretic motion is simulated by the finite element simulation method.The characteristics of the acoustic field and the formation mechanism of the acoustic streaming of the enclosed microfluid are analyzed.The particle motion trajectories are simulated based on the size difference.The effects of acoustic radiation force and viscous resistance dominant conversion mechanism on particle motion in enclosed microfluidics are revealed.An enclosed microfluidic particle acoustophoretic motion experimental system driven by a SSAW was built.The acoustophoretic motion trajectories of micron and submicron particles were observed experimentally,which verified the rationality of the prediction results of the particle acoustophoretic motion model.The deflection characteristics of particles in tilted microchannels were studied.The characteristic parameters affecting particle deflection position and particle aggregation are revealed,and experimental data are provided for the subsequent structural optimization of enclosed microfluidic separation devices.The influence of control parameters and the separation characteristics of particles and cells in the process of enclosed microfluidic particle separation were studied.A mathematical model of particle movement in continuous fluid flow is established by analyzing the movement process of particles in the microchannel.An enclosed microfluidic particle separation experimental platform driven by SSAW was built.The effects of microchannel deflection angle,flow velocity,RF input power,and particle physical properties(size and compressibility)on particle separation were analyzed by numerical simulation and experimental methods.The control parameter adjustment method and optimization strategy to improve the separation efficiency and purity were obtained.Based on the optimized process,the enclosed microfluidic separation device was applied to separate micron(1,3 and 6 μm)and submicron(100,750 and 1000 nm)particles.Separation efficiency is quantified by particle size distribution and particle count.Finally,cell(non-small cell lung cancer cells and peripheral blood mononuclear cells)separation studies were performed.This dissertation systematically studies the SAW-driven microfluidic particle separation technology.Through mathematical model construction,numerical simulation,finite element simulation analysis,and experimental methods,it focuses on solving the problems mentioned earlier in the research of open microdroplets and enclosed microfluidics.Based on the current experimental conditions,the cell separation efficiency is about 85%～91%,the separation purity is about 86%～91%,and the cell viability is greater than 98%,which lays the foundation for applying acoustofluidic particle separation technology in biological engineering.