Synthesis and Characterization of Gelatin-Shelled Microbubbles

Abstract

This study focuses on the synthesis process of gelatin-shelled microbubbles and their characterization. A new method to synthesize gelatin-shelled microbubbles was described. Briefly, Traut’s reagent was used to thiolate gelatin molecules; then sonication forces were placed at the water-air surface of the gelatin solution to generate microbubbles. Thiolated gelatin molecules can form S-S bonds between each other, forming a shell encapsulating air. When gelatin’s concentration is 5% w/v at pH 8, Traut’s reagent is 20 times molar excess of gelatin, and sonication time and amplitude is 45sec and 25% respectively, the microbubbles have a diameter of 1107 nm with a shell thickness of about 175 nm. Among different experiment parameters that can affect the size of the microbubbles, sonication time and amplitude have the biggest impact; and both of them have a positive correlation with bubble sizes. Gelatin’s concentration also has a positive correlation with bubble sizes, although it doesn’t have as big an impact as the other two parameters. Solution pH doesn’t have a clear impact on bubble sizes. When the ratio of Traut’s reagent and gelatin is about 10 to 20, the size of microbubbles tends to be the largest. The functional groups on gelatin can retain their reactivity after forming the shell, making them able to bind various protein or DNA drug molecules. Furthermore, a two-step method was studied using gelatin as an example, which increases the level of thiolation of gelatin. It was found that after gelatin is aminated with EDC and ethylenediamine, up to 8 times more thiol groups can be introduced onto the gelatin surface and potentially increase the shell stability. This two-step method can be especially useful for proteins that may not have many natural thiol and amine groups; and it can potentially provide the opportunities for loading many drug molecules that are previously impossible to be delivered by proteinaceous microbubbles.