Surface Morphology of Lipid-Shelled DSPC:PEG₄₀St Microbubbles

Area of Science:

• Biomedical Engineering
• Materials Science
• Physical Chemistry

Background:

• Lipid-coated microbubbles (MBs) are crucial as ultrasound contrast agents and drug delivery systems.
• The microscale organization of MB shell components is not well understood.
• Understanding shell structure is key to optimizing MB performance.

Purpose of the Study:

• To investigate how lipid composition and environmental factors influence domain formation in MB shells.
• To characterize the microscale organization of 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) and polyoxyethylene-40-stearate (PEG40St) MB shells.
• To correlate shell microstructure with MB properties.

Main Methods:

• Synthesis of DSPC/PEG40St MBs at varying molar ratios.
• Fluorescence microscopy with different probes (FITC-DHPE, NBD-PC).
• Systematic variation of probe concentration, pH, and PEG40St content.
• 3D z-stack reconstruction and time-lapse imaging.

Main Results:

• MB shells exhibited polymorphic, heterogeneous domain structures, not uniform monolayers.
• Increasing PEG40St fraction or pH enhanced heterogeneity among MBs.
• Domains segregated laterally, with protrusions at boundaries; shells showed time-dependent domain condensation and rim formation.
• Heterogeneous fluorescence intensity indicated varied shell compositions within batches.

Conclusions:

• DSPC/PEG40St MB shells segregate into distinct domains, challenging the assumption of homogeneous mixing.
• Shell microstructure significantly impacts MB acoustic properties, stability, and drug loading.
• This understanding can guide the design of improved ultrasound contrast agents and drug delivery vehicles.