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Measuring Acoustic Mobility of Particles by Particle Tracking Velocimetry

Edthofer, Alexander LU (2022) BMEM01 20221
Department of Biomedical Engineering
Abstract
Acoustophoresis is a method to manipulate and move cells or particles suspended in a medium using acoustic waves. The speed of the acoustophoretic motion depends on the cells' acoustic mobility, i.e. their size, density and compressibility relative to the medium. Differences in acoustic mobility can be used to separate particles from each other. Separation is an important tool within biomedical and clinical applications.
In this thesis, we develop a method to measure the acoustic mobility of a particle or cell with Particle Tracking Velocimetry (PTV) software. The acoustic mobility determines the migration velocity, thus it is possible to determine the acoustic mobility by measuring the migration velocity.
As several particles' acoustic... (More)
Acoustophoresis is a method to manipulate and move cells or particles suspended in a medium using acoustic waves. The speed of the acoustophoretic motion depends on the cells' acoustic mobility, i.e. their size, density and compressibility relative to the medium. Differences in acoustic mobility can be used to separate particles from each other. Separation is an important tool within biomedical and clinical applications.
In this thesis, we develop a method to measure the acoustic mobility of a particle or cell with Particle Tracking Velocimetry (PTV) software. The acoustic mobility determines the migration velocity, thus it is possible to determine the acoustic mobility by measuring the migration velocity.
As several particles' acoustic mobilities are determined, they can be used to assess optimal buffer conditions to maximise the relative acoustic mobility between two particles or cells, improving their separation by acoustophoresis.
In this thesis, a simple rectangular microfluidic chip was filled with particles suspended in a solution. The migration of particles due to exposure to an acoustic standing wave field was then repeatedly imaged and the procedure was repeated 20 times collect sufficient data. The particle paths and migration velocities can be extracted by PTV software. By fitting this velocity to a theoretical model the acoustic mobility can be derived.
The experimental set-up and computational model were already present at the Thomas Laurell group at BMC, Lund University where this thesis was conducted. They were, however, lacking sufficient precision and reliability, yielding a wide spread of data points for each experiment and resulting in large variations in measurements between experiments. Thus, the main focus of this thesis primarily revolved around improving the experimental procedures, data processing and the computational model. The long-term goal of this project is to create an easy to use, reliable and rapid method to determine the acoustic properties of any given cell and propose a suitable medium composition for ideal separation.

One improvement of the model is the division of the images into thinner slices to achieve more local and accurate measurements.
Another change was the introduction of a velocity filter, excluding data that stemmed from particles with only minimal movement unrelated to the migration effects induced by the acoustic field.
The thesis also improved and evaluated the experimental set-up in itself, focusing on the usage of fluorescent Polystyrene beads as reference particles as well as evaluating the accuracy of the model and detecting errors in it. This resulted in the discovery of significant differences in the acoustic properties of differently coloured polystyrene particles which were confirmed by an independent experiment.

Finally, the experimental model was used in preliminary measurements of three different breast cancer cell lines' acoustic mobility. (Less)
Popular Abstract (Swedish)
Mätning av partiklars och cellers akustiska egenskapar genom partikelspårningshastighet

I många medicinska sammanhang är man intresserad av att kunna separera olika celltyper från varandra, exempelvis vita blodkroppar från ett blodprov eller insulinproducerande celler från bukspottskörteln. Det finns ett antal olika metoder för att genomföra denna separation. En tämligen ny metod bygger på akustofores, vilket betyder “att flytta med ljud.”

Akoustoforesen bygger på principen att när ljudvågor träffar på en cell knuffar de på den.
Hur mycket den flyttas beror på cellens akustiska mobilitet, vilket är en egenskap beroende på dess storlek, densitet och kompressibilitet (dvs. hur lätt det är för ett material att ändra sin form då det... (More)
Mätning av partiklars och cellers akustiska egenskapar genom partikelspårningshastighet

I många medicinska sammanhang är man intresserad av att kunna separera olika celltyper från varandra, exempelvis vita blodkroppar från ett blodprov eller insulinproducerande celler från bukspottskörteln. Det finns ett antal olika metoder för att genomföra denna separation. En tämligen ny metod bygger på akustofores, vilket betyder “att flytta med ljud.”

Akoustoforesen bygger på principen att när ljudvågor träffar på en cell knuffar de på den.
Hur mycket den flyttas beror på cellens akustiska mobilitet, vilket är en egenskap beroende på dess storlek, densitet och kompressibilitet (dvs. hur lätt det är för ett material att ändra sin form då det utsätts för en kraft) i förhållande till den omgivande vätskans egenskaper.

För att kunna separera celler på ett effektivt sätt med hjälp av ljudvågor behöver man ett sätt att mäta deras akustiska mobilitet. Att mäta deras storlek är relativt enkelt och det finns många väletablerade metoder för att göra det, men att mäta deras densitet och kompressibilitet är inte alls lika etablerat. I detta examensarbete har det utvecklats en metod för att göra just detta.

Metoden går ut på att fylla en mikrokanal, dvs. en kanal med dimensioner på mikrometerskalan, med en vätska som innehåller celler som man vill bestämma egenskaperna av tillsammans med en referenspartikel med redan känd densitet och kompressibilitet, t.ex. mikrometer stora kulor gjorda av glas eller plast.

Sedan skapas det ljudvågor i kanalen med hjälp av en ultraljudsgivare. Genom att använda en lämplig frekvens kan man skapa en stående våg med dess nod precis i mitten av kanalen. Då vågornas rörelse är som minst där kommer cellerna att börja röra sig mot mitten på grund av kollisionerna med vågorna. Medans cellerna och referenspartiklarna rör sig mot mitten tas det en bildserie. Med hjälp av denna bildserie kan man, i ett datorprogram, räkna ut hur snabbt cellerna och partiklarna rörde sig. Eftersom man vet den akustiska mobiliteten hos referenspartiklarna kan man använda den relativa hastigheten mellan cellerna och partiklarna för att räkna ut den akustiska mobiliteten hos cellerna också.

I det här arbetet utfördes det främst konfigering av den experimentella uppställningen samt optimering av datorprogrammet som används vid beräkningarna. För detta ändamål användes främst plastpartiklar i olika storlekar och egenskaper. Uppställningen visar lovande resultat och kan beräkna partiklarnas akustiska mobilitet med försumbara felmarginaler. Initialla tester med tre olika typer av bröstcancerceller visar tydliga skillnader i deras akustiska egenskapar, vilket som kan användas för att anpassa experimentella inställningar och lösningar för att optimera skillnaden i deras akustiska mobilitet, vilket skulle göra separation med hjälp av akustofores av de mycket mer effektiv. (Less)
Please use this url to cite or link to this publication:
author
Edthofer, Alexander LU
supervisor
organization
alternative title
Mätning av partiklars akustiska mobilitet genom partikelspårningshastighet
course
BMEM01 20221
year
type
H2 - Master's Degree (Two Years)
subject
keywords
acoustophoresis, microfluidics, polystyrene, cells, particle tracking velocimetry
language
English
additional info
2022-08
id
9080356
date added to LUP
2022-05-31 14:33:13
date last changed
2022-05-31 14:33:13
@misc{9080356,
  abstract     = {{Acoustophoresis is a method to manipulate and move cells or particles suspended in a medium using acoustic waves. The speed of the acoustophoretic motion depends on the cells' acoustic mobility, i.e. their size, density and compressibility relative to the medium. Differences in acoustic mobility can be used to separate particles from each other. Separation is an important tool within biomedical and clinical applications.
In this thesis, we develop a method to measure the acoustic mobility of a particle or cell with Particle Tracking Velocimetry (PTV) software. The acoustic mobility determines the migration velocity, thus it is possible to determine the acoustic mobility by measuring the migration velocity.
As several particles' acoustic mobilities are determined, they can be used to assess optimal buffer conditions to maximise the relative acoustic mobility between two particles or cells, improving their separation by acoustophoresis.
In this thesis, a simple rectangular microfluidic chip was filled with particles suspended in a solution. The migration of particles due to exposure to an acoustic standing wave field was then repeatedly imaged and the procedure was repeated 20 times collect sufficient data. The particle paths and migration velocities can be extracted by PTV software. By fitting this velocity to a theoretical model the acoustic mobility can be derived.
The experimental set-up and computational model were already present at the Thomas Laurell group at BMC, Lund University where this thesis was conducted. They were, however, lacking sufficient precision and reliability, yielding a wide spread of data points for each experiment and resulting in large variations in measurements between experiments. Thus, the main focus of this thesis primarily revolved around improving the experimental procedures, data processing and the computational model. The long-term goal of this project is to create an easy to use, reliable and rapid method to determine the acoustic properties of any given cell and propose a suitable medium composition for ideal separation.

One improvement of the model is the division of the images into thinner slices to achieve more local and accurate measurements. 
Another change was the introduction of a velocity filter, excluding data that stemmed from particles with only minimal movement unrelated to the migration effects induced by the acoustic field.
The thesis also improved and evaluated the experimental set-up in itself, focusing on the usage of fluorescent Polystyrene beads as reference particles as well as evaluating the accuracy of the model and detecting errors in it. This resulted in the discovery of significant differences in the acoustic properties of differently coloured polystyrene particles which were confirmed by an independent experiment.

Finally, the experimental model was used in preliminary measurements of three different breast cancer cell lines' acoustic mobility.}},
  author       = {{Edthofer, Alexander}},
  language     = {{eng}},
  note         = {{Student Paper}},
  title        = {{Measuring Acoustic Mobility of Particles by Particle Tracking Velocimetry}},
  year         = {{2022}},
}