Targeted microbubbles are used in ultrasound molecular imaging to detect disease specific biomarkers in vivo. To enable selective binding, microbubbles are functionalized with targeting ligands that specifically bind to these biomarkers. However, the lipid shell of microbubbles can phase-separate into structured domains, where targeting lipids preferentially localize in the interdomain region. Therefore, while the global ligand concentration remains constant, their local concentration can be significantly altered. Because microbubble adhesion is governed by local ligand density, shell domains are expected to fundamentally alter binding behavior, yet this critical effect remains largely unexplored.
This project focuses on quantifying the binding strength of monodisperse, targeted microbubbles with well-defined shell domain structures. A flow cell system will be developed of which the channel walls will be functionalized with the model biomarker streptavidin, enabling controlled adhesion of biotinylated microbubbles. Monodisperse microbubbles with either homogenous or phase-separated shells will be produced in-house using microfluidics. By applying controlled flow conditions, the hydrodynamic forces required to detach adherend microbubbles can be accurately determined, allowing quantification of their binding strength. Image analysis tools will be developed in MATLAB or Python to process the experimental data.
Beyond the initial focus on binding strength, this project can be extended to study how both local and global ligand concentrations influence adhesion. Several key questions remain open. Does the presence of domains alter the effective contact area between the microbubble and the surface? This can be addressed using confocal microscopy by acquiring high-resolution z-stacks of bound MBs.
In addition, adherend microbubbles exhibit oscillatory dynamics that differ from those of freely floating microbubbles due to interactions with the nearby boundary. However, a direct comparison between microbubbles with and without shell domains, while keeping their size constant, has not been explored. This project provides a unique opportunity to address this gap and uncover how shell microstructure influences both biding and ultrasound-driven acoustic response.
