Lipid-Coated Nanobubbles in Plants

One of the more surprising occurrences of bulk nanobubbles is in the sap inside the vascular transport system of flowering plants, the xylem. In plants, nanobubbles are subjected to negative pressure in the water and to large pressure fluctuations, sometimes encompassing pressure changes of several MPa over the course of a single day, as well as wide temperature fluctuations. Here, we review the evidence for nanobubbles in plants and for polar lipids that coat them, allowing nanobubbles to persist in this dynamic environment. The review addresses how the dynamic surface tension of polar lipid monolayers allows nanobubbles to avoid dissolution or unstable expansion under negative liquid pressure. In addition, we discuss theoretical considerations about the formation of lipid-coated nanobubbles in plants from gas-filled spaces in the xylem and the role of mesoporous fibrous pit membranes between xylem conduits in creating the bubbles, driven by the pressure gradient between the gas and liquid phase. We discuss the role of surface charges in preventing nanobubble coalescence, and conclude by addressing a number of open questions about nanobubbles in plants.

Microbubble-liposome conjugate: Payload evaluation of potential theranostic vehicle

Liposome–microbubble conjugates are considered as better targeted drug delivery vehicles compared to microbubbles alone. The microbubble in the integrated drug delivery system delivers the drug intracellularly on the target, whereas the liposome component allows loading of high drug dose and extravasation through leaky vasculature. In this work, a new high yielding microbubble production method was used to prepare microbubbles for formulation of the liposome-conjugated drug delivery system. In formulation process, the prepared liposome of 200 nm diameter was attached to the microbubble surface using the avidin–biotin interaction. The analysis of the confocal scanning laser microscope images showed that approximately 8 × 10⁸ microbubbles per millilitre (range: 2–7 μm, mean size 5 ± 0.5 μm) can be efficiently conjugated to the liposomes. The method of conjugation was found to be effective in attaching liposome to microbubbles.

Nanobubbles: a new paradigm for air-seeding in xylem

Long-distance water transport in plants relies on a system that typically operates under negative pressure and is prone to hydraulic failure due to gas bubble formation. One primary mechanism of bubble formation takes place at nanoporous pit membranes between neighboring conduits. We argue that this process is likely to snap off nanobubbles because the local increase in liquid pressure caused by entry of air-water menisci into the complex pit membrane pores would energetically favor nanobubble formation over instant cavitation. Nanobubbles would be stabilized by surfactants and by gas supersaturation of the sap, may dissolve, fragment into smaller bubbles, or create embolisms. The hypothesis that safe and stable nanobubbles occur in plants adds a new component supporting the cohesion-tension theory.