Ligand Distribution and Lipid Phase Behavior in Phospholipid-Coated Microbubbles and Monolayers

Area of Science:

• Biomaterials Science
• Nanotechnology
• Ultrasound Imaging

Background:

• Phospholipid-coated microbubbles are crucial for molecular imaging and drug delivery.
• Their targeting efficiency depends on microbubble coating microstructures.
• Understanding ligand distribution and lipid phase behavior is essential.

Purpose of the Study:

• To investigate ligand distribution and lipid phase behavior in targeted microbubbles.
• To correlate these properties with microbubble coating microstructures.
• To assess the impact of lipid handling methods on microbubble characteristics.

Main Methods:

• Studied ternary lipid mixtures (DPPC/DSPC, PEG40-stearate, DSPE-PEG2000) forming microbubble coatings.
• Utilized Langmuir trough for monolayer analysis of lipid phase behavior.
• Employed infrared reflection absorption spectroscopy (IRRAS) to confirm PEG conformation changes.
• Analyzed ligand distribution and lipid phase area in microbubbles (1.5-8 μm diameter).

Main Results:

• Ternary mixtures exhibited a unique transition plateau due to PEG conformation changes (mushroom to brush).
• DPPC microbubbles showed homogenous ligand distribution and less liquid condensed (LC) phase area.
• DSPC microbubble ligand distribution and LC phase area varied with lipid handling (direct vs. indirect method).

Conclusions:

• Lipid handling prior to microbubble production critically influences DSPC-based microbubble properties.
• The indirect method (organic solvent) yielded homogenous ligand distribution and larger LC phase area in DSPC microbubbles.
• Optimized lipid handling is vital for developing effective targeted microbubbles for imaging and drug delivery.