Ultrasound-and-microbubble-mediated Drug Delivery in Microvascular Networks

Thesis (Master's)--University of Washington, 2017-08In recent research, ultrasound and microbubble-mediated membrane perforation (i.e. sonoporation) has shown great promise in improving the efficacy and delivery efficiency of drugs and genetic materials to tumor cells and malignant tissues. However, the exact mechanism of sonoporation and the optimal ultrasound parameters and microbubble concentration to produce sonoporation in vivo remain unclear. Furthermore, most attempts to study sonoporation have used simple in vitro cell-monolayer setups that failed to capture the complex human vascular environment and the microbubble-vessel interactions seen in vivo. Therefore, there exist great needs to 1) quantitatively assess the individual effects of ultrasound parameters and microbubble concentration on producing sonoporation, and 2) develop a perfusable in vitro microvascular model which features in vivo-like flow characteristics, 3D geometry, and biotransport properties. In this work, we evaluated 1) the attenuation of ultrasound at different microbubble concentrations, 2) the behavior of microbubbles at different acoustic pressures. 3) the efficacy of sonoporation in an acoustically transparent in vitro cell-monolayer setup. Our group has also successfully developed an endothelialized 3D microvascular model that recapitulates the complex structure and flow characteristics found in vivo, and this model was used to evaluate the efficacy of sonoporation in an in vivo-like environment. Our results showed that 1) acoustic attenuation increased with microbubble concentration and was dependent on the source acoustic pressure, 2) microbubble destruction and acoustic streaming increased with acoustic pressure, number of cycles, and duty cycle, 3) repeated ultrasound pulse at acoustic pressure greater than 500 kPa could be needed to induce sonoporation in vitro, and 4) based on the sonoporation data obtained with our in vitro microvascular model, the acoustic pressure and microbubble concentration needed to induce sonoporation in vivo could be much higher than expected from the results obtained with in previous in vitro studies. Our findings underscore the importance of using in-vivo-like microvascular models to study sonoporation