A multiphase flow study of bubbles traveling through bifurcations for a novel gas embolotherapy application.

Abstract

Embolotherapy involves introduction of foreign objects into the bloodstream, normally solid, to occlude the flow of blood for therapeutic reason. The primary obstacle for an effective use of embolotherapy is the inability to accurately control the target region, where the foreign objects get trapped and delivering the objects in a relatively homogenous manner. Because of this it is essential to understand the fluid mechanics and transport of emboli in these flow situations to define experimental and theoretical approaches that can reveal important system parameters which govern the distribution and entrapment of emboli. This dissertation investigates experimentally, theoretically and computationally the above mentioned for a novel type of gas embolotherapy, which uses gas bubbles as emboli to treat cancer. The transport of long gas bubbles, suspended in liquid, through symmetric bifurcations is investigated experimentally, theoretically and computationally as a model of cardiovascular gas bubble transport for gas embolotherapy and air embolism. The effects of roll angle (the angle the plane of the bifurcation makes with the horizontal), capillary number (a dimensionless indicator of flow), and bubble volume (or length) on the splitting of bubbles as they pass through the bifurcation are examined experimentally and theoretically. With the computational model we varied bifurcating angle, driving pressure and pressures in the daughter branches. Splitting is observed to be more homogenous at higher capillary numbers or higher pressures and lower roll angles. Lodging of cardiovascular gas bubbles is investigated in a microfluidic model of small arteriole bifurcations. The driving pressure, bubble size and geometrical parameters are varied, and their effects on the bubble lodging are assessed. It is possible to occlude an entire bifurcation and multiple bifurcation microchannels with bubbles. The results presented in this dissertation are encouraging for gas embolotherapy to treat cancer. This dissertation provides new information about the dynamics of bubble lodging, as well as predicts at what level of vasculature bubbles are more likely to lodge. Also the computational model can be used for further investigation of specific in-vivo situations.