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

Abstract

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.

Use of Nanobubbles to Improve Mass Transfer in Bioprocesses

“…Although nanobubbles offer numerous benefits for bioprocesses, several potential limitations and drawbacks need to be considered. High concentrations of nanobubbles, especially those containing reactive oxygen species, can induce oxidative stress in cells, damaging cellular components, such as membranes, proteins, and DNA, and potentially reducing cell viability and productivity [77]. Additionally, nanobubbles formed by electrolysis may alter the pH of the solution, affecting the growth and metabolism of certain microorganisms that are sensitive to pH changes.…”