Effects of Filling Gas Composition on Microbubble Material Properties

Lipid-Shelled microbubbles are highly echogenic gas-filled particles ranging from 1 to 10 microns. The shell typically contains varying amounts of PEGylated lipids to improve biocompatibility and reduce coalescence. The filling gas type and PEG concentration immensely affect fundamental characteristics such as size distribution, material properties, attenuation, and stability. Here we investigated the extent of these changes by studying four different PFB-air-filled microbubble groups produced by mechanical agitation with varying PFB-air concentration and PEG ratios. We measured the attenuation of microbubbles under low ultrasonic excitation with a 5 MHz flat transducer. The measured attenuation was used to determine microbubble material properties using an interfacial rheological model. The interfacial elasticity was found to be significantly higher for lower PFB-air ratios, while the effects of PEG ratios were little. Additionally, the yield of microbubbles was higher for lower PFB-air ratios, although the mean size remains similar across the various groups studied. The findings offer new insights into both the stabilization of freshly formed microbubbles and their in vitro stability.