Bubble Dislodgment in a Capillary Network with Microscopic Multichannels and Multibifurcation Features

Bubble lodgement in a complex capillary network is a common issue in many industrial and biological processes. In medical applications, embolotherapy, a potential cancer treatment, utilises bubble lodgement to achieve the occlusion of the arteriole or capillary in targeted sites. The lodged bubbles block microvessels to restrict blood supply to tumours and thus control the growth of tumour cells. Another potential cancer treatment microbubble-loaded drug delivery has been investigated for decades, while the safety issues still hinder its transform from bench to clinics. The precise control of bubble lodgement at the targeted sites will significantly increase the therapeutic efficacy of treatment and decrease the side effects, such as the drug accumulation and distribution in healthy tissues.

We believe that a thorough understanding of bubble lodgement and dislodgment in a complex capillary network can contribute to control the bubble flow in blood vessels and improve the feasibility and efficiency of transport, by helping us understand where the bubble ultimately lodges, whether the bubble can be lodged and dislodged properly, and the persistence time of microbubbles lodged around the targeted sites.

In the past, research work reported in the literature only investigated bubble dislodgment in single straight channels and Y-type or U-type channels and did not consider the effect of network complexity on the dislodgment. Here in this paper, we focus on the pressure required to dislodge single bubbles from a microscopic capillary network and investigate the factors affecting the dislodging pressure to facilitate the precise control of bubble flows in porous media.

We designed a capillary network with multibifurcation and a smoothly changed diameter to closely mimic the structure of the physiological vascular networks and conducted more than 600 bubble dislodgment experiments to understand the effect of the network structure, channel dimensions, and bubble length on the dislodging pressure.

The results indicate that the network structure is a dominant factor affecting the dislodging pressure that increases with the increase in network complexity. The effect of bubble length on the dislodging pressure depends on the bubble length. When the bubble length is less than a certain value, which is around 2 mm in this study, the dislodging pressure increases significantly with the decrease of bubble length. When the bubble length is larger than 2 mm, the dislodging pressure is independent of the bubble length.

To explain the bubble dislodgment in complex capillary networks, we have also derived a one-dimensional model to fully describe the bubble dislodgment in a complex capillary network and to predict the dislodging pressure. The model agrees well with the experimental results and indicates that the dislodging pressure is the function of bubble length, channel dimension, and network structure.

For more information on this work, you can read the original paper here: https://www.liebertpub.com/doi/pdf/10.1089/soro.2018.0026