When Nanobubbles, Bubble!

Nanobubbles are very small bubbles of gas in a liquid. These bubbles are in the  nanoscopic range in that they are 1000 nm or less in diameter. For the purpose of nanobubble therapy however, the ideal size (“island of stability”) is 50 nm - 200 nm in diameter, with the average size of each bubble at about 100 nm, 500 times smaller than a microbubble. For some perspective, an average human hair is 100,000 nm-- 1,000 times wider than a single 100 nm bubble.

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Nanobubbles are considered an effective therapeutic because of their unique physical and chemical properties. 

Physically: Nanobubbles possess the ability to stay in water for long periods of time (months or even years) whereas microbubbles or larger bubbles only stay in water for hours (think how fast your soda loses its carbonation). Staying in water for such long periods of time is advantageous when creating packaged goods such as oxygenated nanobubble water like O₂n water.^[1] In addition, a valuable technical advantage that is gained by this stability is the ability to cycle the same water through the nanobubbler multiple times, thereby increasing the nanobubble concentration, which is crucial to get therapeutic value. There are several reasons for nanobubble’s ability to stay in water:

Size - Nanobubbles’ nanoscopic size allows for their buoyancy to be almost exactly equal to gravitational forces, this creates the equal up and down forces which lets nanobubbles stay suspended in liquid for months or years. This is in contrast to larger bubbles, whose large buoyant forces overcome gravity and push them upward, forcing them to leave the water (think of blowing bubbles in water with a straw). What this means is that any sort of coalescence (combining) of bubbles is detrimental to the lifespan and efficacy of nanobubbles.

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Because of their size, nanobubbles are influenced by what is known as Brownian motion, which is simply random motion in and around water. Brownian motion is important because it distributes nanobubbles evenly throughout the water

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Nanobubbles’ strong negative charge causes bubble-to-bubble repulsion, preventing bubbles from coalescing into larger bubbles. Bubble-to-bubble repulsion is related to the concept of zeta potential, which is highly correlated with nanobubble stability, and thus lifespan and potential for increased concentrations. 

To learn more about zeta potential or how we have optimized various physical properties of nanobubbles, to confer maximum efficacy for therapeutic benefit.^[2]

Nanobubbles’ extremely large internal pressure prevents bubbles from losing surface charge, thereby allowing bubbles to maintain zeta potential and their long lifespan.^[1]

Chemically: Liquids like water are limited in the amount of dissolved gas they can hold. The maximum dissolved gas concentration of a liquid is known as its saturation point. The saturation point of a liquid is proportional to the partial pressure above the liquid-- a principle known as Henry’s Law. Partial pressure is defined as the pressure of a gas if it occupied a given volume by itself (i.e. if gas A, B and C were the same container, the partial pressure of gas A would be the same as removing gas B and C from the container, as shown in the figure below). Nanobubbles, however, are not considered to be “dissolved” in water, and thus do not contribute to the saturation point of water. Instead, nanobubbles act more like very small cavities of oxygen that are in, but separate from water. What this means in practice is that nanobubbles offer the ability to supersaturate water. This phenomena has been seen in peer-reviewed articles where nanobubbles increased partial pressure by more than five times their original amount, as shown below.^[2]

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The following graph shows water saturated with nanobubbles vs microbubbles vs control. The partial pressure is highest (by a significant margin) for fine microbubbles/nanobubbles.^[2]

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Notes: Oxygen fine micro/nanobubbles were generated using a dedicated micro/nanobubble aerator, with an oxygen gas supply of 1.5 L/minute for 15 minutes, and the immediate application of brief sonication. Oxygen macrobubbles were generated in 150 mL of ultrapure water using porous ceramic with an oxygen gas supply of 1.5 L/minute for 15 minutes. The oxygen partial pressure in ultrapure water was measured by blood gas analysis. Data are presented as the mean ± standard error of the mean of five separate experiments, each performed in duplicate. **P<0.01.” ^[2]

This is in contrast to microbubbles, for example, which rise to the top of water, and don’t provide much therapeutic value. In other words, nanobubbles can increase the water’s oxygen concentration by letting the water contain its maximum dissolved oxygen content AND in addition, the oxygen in the nanobubbles themselves, while microbubbles escape the water too quickly and thereby are notable to contribute to transdermal oxygenation.

We detail this concept even more in our optimization article.^[3]

Nanobubble immersion therapy can be as simple as having a user lay in a tub of water saturated with nanobubbles, however, if done incorrectly, this will not provide any therapeutic value. Instead, we at oval.bio have focused on the two most important factors that can affect the efficacy of nanobubbles: the size and concentration of bubbles.

Size: Repeated: Bubbles should sit in a size range known as the island of stability-- a range from 50 nm to 200 nm. A bubble smaller than 50 nm will collapse and become dissolved oxygen. And if the water is already at maximum saturation, the oxygen will simply escape. Bubbles larger than 200 nm will coalesce and then escape the water rapidly.

Refer to the figures below to see the range of diameters our nanobubbler produces (mean 115.9 nm and mode 87.4 nm).

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Additionally, having smaller nanobubbles allows us to saturate water with a greater volume (and thus concentration) of oxygen when compared to traditional bubbles. In essence, by having smaller bubbles, we are able to pack water with more oxygen. This is similar to filling a bottle with sand as opposed to pebbles. The sand, like the nanobubbles, allows for a much greater density in the same volume of space.

What this means in practice is that it is better to aim for the lower end of the island of stability, which is what our nanobubbler does.

Concentration: Repeated: It is known that if the water has higher concentrations of oxygen that the body, the body will absorb oxygen from the water.^[3] This is because of a phenomena known as osmosis, where higher levels of oxygen in water and lower levels of oxygen in the body cause the oxygen from the water to start to transfer into the body. The higher the concentration of oxygen in water, the greater the quantity of oxygen that can be transferred into the body.

Since nanobubbles increase the dissolved oxygen potential of water, we are able to saturate the body with a higher quantity of oxygen.

Sources:

[1] https://pubmed.ncbi.nlm.nih.gov/22985594/

[2] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4181745/

[3] https://www.sciencedirect.com/topics/neuroscience/osmosis