Nanobubbles

My Christmas Blog 2021 looks at the fluid physiology of nanobubbles.

Clinicians are comfortable with solution of gas molecules in aqueous solutions. We measure the partial pressures of vital gases in blood very frequently, and understand that greater pressure means more molecules (of O2, CO2 etc) per unit volume. We can draw diagrams of O2 molecules diffusing from erythrocytes to plasma to endothelium to interstitium to cell membrane to cytoplasm and at last to fuel energy creation in mitochondria. We worry (or at least some of us do) about obstacles to the smooth passage of O2 into, and CO2 out of, of our patients’ cells. Now there is a new kid on the block; nanobubbles and their contributions to oxygen transfer efficiency.

Nanobubbles are very small bubbles. I’d like to thank Moleaer for providing much of the following information about nanobubbles. Let’s start with an infographic.

Joseph Priestley was employed as Librarian and Tutor to Lord Shelburne at Calne, in Wiltshire, during the 1770s when he did his first work on fine bubbles, and how to make them. A good man, and a busy scientist, he left Johann Jacob Schweppe, a watchmaker from Geneva, to make all the money out of carbonated drinks, which were believed to cure scurvy and be generally Good for Health. Microbubbles are smaller than one hundredth of a millimetre in diameter, and have found several uses in modern therapeutics. Nanobubbles are smaller than 200 nm and have some remarkable characteristics, among which the first is that they are invisible to the naked eye. Let us consider some further properties of nanobubbles.

  • Nanobubbles are not ‘lighter than water’. They are neutrally buoyant and can remain suspended in water for weeks without rising to the surface and off-gassing.
  • Nanobubbles have a strong negative surface charge that prevents them from coalescing, and enables them to physically separate small particles or molecular strands.
  • Nanobubbles remain stable in solution until they interact with surfaces. They have a strong negative surface charge that keeps them stable and enables them to continuously participate in and stimulate physical, biological, and chemical interactions.
  • When nanobubbles are stimulated, they destabilize and collapse, releasing the hydroxyl radical, one of the strongest-known oxidizers.
  • Nanobubbles are present in biological aqueous solutions, including of course the plasma whose blood gas tension is so familiar to us. They ensure an enormous total bubble surface area remains in contact with water to deliver hyper-efficient gas transfer.

After several years about the importance of nanobubbles, their story is moving into endotheliology.

“The endothelial surface layer seems to be a respiratory organ contiguous with the flowing blood, an extension of, and a ‘lung’ in miniature. This interpretation may have far-reaching consequences for physiology.”

Reines BP, Ninham BW. Structure and function of the endothelial surface layer: unraveling the nanoarchitecture of biological surfaces. Q Rev Biophys. 2019;52:e13.

So here is Christmas Holiday Reading for Fluid Physiologists. Barry Ninham proposes that nanobubbles explain why the glycocalyx layer is robust enough to bounce red blood cells away from a vessel wall. When I first made a conference presentation (at the Royal Society of Medicine) on the glycocalyx role in Starling physiology, my old friend Monty Mythen had the strongest rebuttal – the glycocalyx is way too fragile to have any vital importance. If Ninham is right about the endothelial surface layer as a lung in miniature, we have even more imperative as clinicians to educate our peers about it, to investigate it, and to protect it from avoidable injuries.

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