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Acoustic and Mechanical Properties of Microbubbles Stabilized by Polymeric Nanoparticles
Norwegian University of Science and Technology, Faculty of Natural Sciences and Technology, Department of Physics.
2013 (English)MasteroppgaveStudent thesis
Abstract [en]

This thesis examines acoustic and mechanical properties of microbubbles stabilized by poly(butyl cyanoacrylate) nanoparticles. The microbubbles are developed with the purpose of being applied in combination with ultrasound as a novel drug delivery system to tumors. Knowledge about the acoustic and mechanical properties is essential to understand the interaction between ultrasound and the microbubbles, their drug delivery potential and stability in the circulatory system. Microbubbles with different surfactant proteins, average diameter, and nanoparticle batches are analyzed and compared in this work. Backscattered power and attenuation of ultrasound waves propagating through a suspension of microbubbles are measured in the frequency range 1-20 MHz. The measurements are done with microbubbles suspended in a sample chamber in a water tank. Attenuation are measured by using the same ultrasound transducer both for transmit and receive. The attenuation coefficients are plotted as function of frequency, and theoretical attenuation spectra calculated from the Church model and the Ho model are tted to the experimental spectra by appropriate estimation of viscoelastic properties of the microbubble shell. Using casein as a surfactant protein is found to increase the shear modulus and viscosity of the shell compared to when Bovine Serum Albumin (BSA) is used. Microbubbles with BSA as surfactant protein and smaller average diameter show higher shear modulus, but lower viscosity compared to when the average diameter is larger. The backscatter is received with a transducer different from the transmit transducer. When a transmit transducer with center frequency 1 MHz is used, the scatter spectra display higher harmonics at pressures above 5-15 kPa. Furthermore, destruction takes place above 170 kPa, but apparently more for the microbubbles with casein rather than BSA as surfactant protein. Smaller microbubbles seem to exhibit more resistance against destruction. Measurements of microbubble shell elasticity is performed using atomic force microscopy (AFM) by applying nanoscale compressions (up to 500 nN) with a at cantilever on isolated nanoparticle-stabilized microbubbles. Values of the Young's modulus are found by fitting obtained force-deformation curves to the simple theoretical Reissner model. In accordance with the attenuation measurements, the results indicate that the casein microbubbles have higher Young's modulus than BSA microbubbles. The shell thickness is assumed to be 150 nm. A linear relation between the Young's modulus and the diameter is found for the microbubbles with casein as surfactant protein.

Place, publisher, year, edition, pages
Institutt for fysikk , 2013. , 104 p.
URN: urn:nbn:no:ntnu:diva-22549Local ID: ntnudaim:9946OAI: diva2:649794
Available from: 2013-09-19 Created: 2013-09-19 Last updated: 2013-09-19Bibliographically approved

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