Acoustic and Mechanical Properties of Microbubbles Stabilized by Polymeric Nanoparticles
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
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.
IdentifiersURN: urn:nbn:no:ntnu:diva-22549Local ID: ntnudaim:9946OAI: oai:DiVA.org:ntnu-22549DiVA: diva2:649794
Davies, Catharina de Lange, Professor