Optical and Acoustic Characterization of Phase-Shift Droplets with Varying Shell Compositions
Sugandha Chaudhary1, Anuj Kaushik1, Bachir A Abeid2
1Department of Radiology, University of Michigan, Ann Arbor, Michigan 48109-5667, United States.
Langmuir : the ACS Journal of Surfaces and Colloids
|March 5, 2025
Summary
The shell composition of perfluorocarbon droplets minimally impacts their acoustic droplet vaporization (ADV) thresholds and payload release. However, lipid shells exhibit greater stability and slower degradation after ADV compared to protein shells.
Area of Science:
- Biomedical Engineering
- Acoustic Physics
- Materials Science
Background:
- Shell-stabilized, phase-shift droplets of perfluorocarbon are promising for ultrasound diagnostics and therapeutics.
- The influence of shell composition on acoustic droplet vaporization (ADV) droplets is less understood compared to conventional microbubbles.
Purpose of the Study:
- To investigate how lipid, protein, and polymer shell compositions affect the stability, ADV dynamics, growth, payload release, and acoustic response of perfluorohexane droplets.
- To compare the behavior of different shell compositions under ultrasound in tissue-mimicking hydrogels.
Main Methods:
- Micron-sized, payload-carrying droplets with lipid, protein, or polymer shells were fabricated using a microfluidic platform.
- Optical (ultrahigh-speed, timelapse confocal microscopy) and acoustic characterizations were performed in fibrin-based hydrogels.
- Fluorescent markers were used to track shell integrity and payload release post-insonation at 2.5 and 9.6 MHz.
Main Results:
- Lipid-coated droplets showed up to 20% lower maximum expansion ratios compared to protein- and polymer-coated droplets.
- Payload release rates were rapid (order of magnitude faster than bubble growth) and showed minimal dependence on shell type.
- Lipid shells retained fluorescence longer (40% at 120s) than protein shells (completely diminished), indicating better stability. ADV and inertial cavitation thresholds were similar across all shell types.
Conclusions:
- Shell composition has a limited effect on the acoustic droplet vaporization (ADV) and inertial cavitation thresholds of perfluorohexane droplets.
- While shell composition influences droplet expansion and long-term stability, it minimally affects rapid payload release kinetics.
- Lipid shells offer enhanced stability post-ADV compared to protein shells, which may be relevant for specific ultrasound applications.
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