The microbubble suspension prepared using sonication method generally has a broad size distribution (0.1 - 20 µm or more). Therefore, microbubbles sample are treated to size isolation using centrifugal separation technique to produce a very narrow distribution of 3 - 5 µm microbubbles. At present, we are investigating the effect of various material properties such as effect of various additives, microbubbles aqueous storage medium, aqueous solubility of gases used on size, size distribution, Ostwald ripening, and on the stability of microbubbles.

Lipids, proteins or any other polymers with surface functional groups such as free amine groups/ hydroxyl groups on the microbubble surface can be used for the purpose of PEGylation, e.g. if BSA/HSA is used as a shell material, NHS-mPEG can be used for surface functionalization. The fluorescent PEG can be used to estimate the extent of PEGylation efficiency. Various other targeted moieties can also be tethered on to the microbubbles using the available surface functional groups. It was found that PEGylation reduces the immunogenicity of the protein microbubbles.

Microbubbles are highly echogenic and hence can produce a good ultrasound backscatter as the gaseous core, being compressible, can expand and contract when subjected to ultrasound. This backscatter can be used for diagnostic imaging purposes. In-vitro studies have shown that protein microbubbles, non-PEGylated/PEGylated were able to produce a good contrast. The protein microbubbles stored for 4 months also retained the contrast enhancing abilities.