Review on the Significant Interactions between Ultrafine Gas Bubbles and Biological Systems.

Having sizes comparable with living cells and high abundance, ultrafine bubbles (UBs) are prone to inevitable interactions with different types of cells and facilitate alterations in physiological properties. The interactions of four typical cell types (e.g., bacterial, fungal, plant, and mammalian cells) with UBs have been studied over recent years. For bacterial cells, UBs have been utilized in creating the capillary force to tear down biofilms. The release of high amounts of heat, pressure, and free radicals during bubble rupture is also found to affect bacterial cell growth. Similarly, the bubble gas core identity plays an important role in the development of fungal cells. By the proposed mechanism of attachment of UBs on hydrophobin proteins in the fungal cell wall, oxygen and ozone gas-filled ultrafine bubbles can either promote or hinder the cell growth rate. On the other hand, reactive oxygen species (ROS) formation and mass transfer facilitation are two means of indirect interactions between UBs and plant cells. Likewise, the use of different gas cores in generating bubbles can produce different physical effects on these cells, for example, hydrogen gas for antioxidation against infections and oxygen for oxidation of toxic metal ions. For mammalian cells, the importance of investigating their interactions with UBs lies in the bubbles' action on cell viability as membrane poration for drug delivery can greatly affect cells' survival. UBs have been utilized and tested in forming the pores by different methods, ranging from bubble oscillation and microstream generation through acoustic cavitation to bubble implosion.

Crucial Role of Surfactants in Improving the Extraction Efficiency of ß-Amyrin from Dischidia major Using Ultrasound-Assisted Extraction Coupled with Gas Bubble Flotation.

Ultrasound-assisted extraction coupled with gas bubble flotation was developed as a green method for extracting ß-amyrin fromDischidia major. The solvent system was water:ethanol (9:1). To improve the adsorption of ß-amyrin onto the air/liquid interface during flotation, surfactants were employed; however, the positive effect was only observed with cationic surfactants. High-performance liquid chromatography with spectrophotometric detection (HPLC-PDA) was, for the first time, applied to quantify the ß-amyrin content in D. major and its extracts. With the assistance of surfactants, the foam layer collected from flotation showed high selectivity toward ß-amyrin. The product content was notably increased after surfactants had been removed from the solution.