UC Irvine

Cancer is still a major public health challenge worldwide in 2023, despite the progress madein its treatment. Some types of cancer, like liver cancer and uveal melanoma, still have poor survival rates, and metastasis, the spread of cancer to other parts of the body, poses significant challenges for effective management and control. Innovative therapies such as targeted therapies and immunotherapies have shown promising results in treating various types of cancer, and further research and development in this field are crucial to addressing the challenges posed by cancer. One of the innovative therapies is the use of microbubbles for targeted cancer therapy. Microbubbles can be activated using ultrasound, causing them to rupture and release therapeutic agents like chemotherapeutic drugs at the tumor site. Additionally, microbubbles can create temporary pores in the cell membrane, enhancing the delivery of therapeutic agents to the tumor site. Despite their potential, using microbubbles for targeted cancer therapy poses several challenges. One major challenge is their stability and loading capacity, which can reduce their effectiveness in delivering the targeted drug. Another challenge is producing a monodisperse population of microbubbles, crucial in targeted cancer therapy to improve their circulation and interaction with tumor cells. Ongoing research is focused on optimizing the design of microbubbles and exploring their potential in combination with other therapies for a wide range of cancer types. This dissertation addresses the primary challenges of using microbubbles for theranostic applications by: (i) creating a simple and effective process for producing stable and monodispersed single emulsion microbubbles (SEBs) using droplet microfluidic technology (ii) creating a simple and effective process for producing stable double emulsion microbubbles (DEBs) using a microfluidic flow-focusing platform (iii) enhancing the stability and functionality of DEBs by incorporating a gold nanoparticle (GNP) protective shell. First, a microfluidic device is designed and optimized to produce monodisperse and stable single-layer microbubbles. Additionally, a portable and automated gas saturation unit is introduced to saturate the phospholipid solution with the C4F8 gas before each experiment, a critical step for the monodispersed production of microbubbles. Our results indicate that using a microfluidic platform, bubbles with a monodispersity as low as 3% can be produced, a significant improvement compared to commercial microbubbles with a PDI that can vary between 20-50%. Two commonly used phospholipid formulations are explored, and the short- term and long-term stability of the resulting microbubbles are compared. The long-term stability of the microbubbles is also investigated in RPMI solution, a common cell culture medium. Our results show that the bubbles produced using the optimized phospholipid solution from the previous section remain stable inside RPMI and at 37°C for up to eight days. The effects of flow parameters on SEB size for the chosen phospholipid formulation are also examined. Secondly, to address the need for a simple and effective process for producing monodisperse and stable microbubbles with higher drug loading capacity, a microfluidic device is designed and optimized to generate highly monodispersed, phospholipid-stabilized oil-shell microbubbles using the optimized phospholipid formulation from the first step. Additionally, the stability and microstructural evolution of these microbubbles are investigated by microscopy and machine-learning-assisted segmentation techniques at different phospholipid and gold nanoparticle concentrations. The double-emulsion microbubbles, formed with the combination of phospholipids and gold nanoparticles, are equipped with a protective gold nanoparticle shell that is not only acting as a steric barrier against gas diffusion and microbubble coalescence but also alleviating the progressive dewetting instability and the subsequent cascade of coalescence events. The research findings indicate that the addition of GNPs to the lipid solution mixture leads to a more than 17-fold increase in the concentration of DEBs that remain in the sample after 60 minutes. Moreover, when GNPs are added to the phospholipid mixture, the number of dewetted oil droplets decreases by over 50%.