Optical characterization of individual liposome-loaded microbubbles

Newly developed liposome-loaded (LPS) microbubbles are characterized by comparing their oscillating response with standard phospholipid-coated (bare) microbubbles using the ultra-high speed imaging (Brandaris 128) camera. A study of the shell properties indicate nearly the same shell elasticity and a higher shell viscosity for LPS bubbles than for bare bubbles. A frequency and pressure-dependent bubble acoustical behavior study shows a higher threshold for the initiation of bubble vibrations for LPS bubbles. In addition, an “expansion-only” behavior was observed for up to 69% of the investigated LPS bubbles which mostly occurred at lower acoustic pressures (≤30 kPa). Liposome attachment stability were studied using fluorescence imaging. The internal relationship among morphological structure, shell properties and ultrasonic behavior of LPS bubbles by optical characterization facilitate preclinical study and clinical application of LPS bubbles in ultrasound triggered drug delivery system.