Shell properties and concentration stability of acoustofluidic delivery agents

Area of Science:

• Acoustofluidics
• Biomaterials Science
• Ultrasound Contrast Agents

Background:

• Ultrasound contrast agents (UCAs) are essential for diagnostic imaging.
• Microbubble-based UCAs, like Definity™, are widely used but can be unstable.
• Acoustofluidics offers novel methods for manipulating and characterizing microbubbles and liposomes.

Purpose of the Study:

• To compare the shell elastic properties and number-concentration stability of novel acoustofluidic liposomes against Definity™ microbubbles.
• To evaluate the impact of temperature on the mechanical properties of both liposomes and microbubbles.
• To provide critical data for designing effective acoustofluidic delivery systems.

Main Methods:

• Frequency-dependent acoustic attenuation measurements to determine shell stiffness (Sp) and friction (Sf).
• Tunable Resistive Pulse Sensing (TRPS) for analyzing bubble size distribution and number-concentration over time.
• Controlled temperature variations (25°C to 37°C) to assess thermal effects on shell properties.

Main Results:

• Liposomes exhibited lower stiffness (Sp = 0.11 N/m) and friction (Sf = 0.31 × 10⁻⁶ Kg/s) than Definity™ (Sp = 1.53 N/m, Sf = 1.51 × 10⁻⁶ Kg/s) at 25°C.
• At physiological temperature (37°C), liposome stiffness increased by 27% while microbubble stiffness decreased by 23%.
• Liposomes maintained >80% number-concentration for 24 hours, significantly outperforming Definity™ (27% stability).

Conclusions:

• The novel liposomes possess distinct, tunable elastic properties compared to conventional microbubbles.
• Liposomes demonstrate superior long-term stability and more favorable thermal response for acoustofluidic applications.
• These findings support the potential of liposomes as advanced agents in acoustofluidic delivery systems.