Evolution of bubbles from gas micronuclei formed on the luminal aspect of ovine large blood vessels
Introduction
Using atomic force microscopy, it has been shown, mainly in the last decade, that tiny, flat gas nanobubbles measuring 5–100 nm form spontaneously when a smooth hydrophobic surface is submerged in water containing dissolved gas (Tyrrell and Attard, 2001, Yang et al., 2007). A number of theories have been proposed in explanation of the formation and stability of these nanobubbles (Seddon et al., 2011, Weijs et al., 2012). In ultrasound irradiation, rectified diffusion increased the volume of the nanobubbles (Brotchie and Zhang, 2011), suggesting that they might expand in a state of gas supersaturation. In our previous studies (Arieli and Marmur, 2011, Arieli and Marmur, 2013), these nanobubbles were shown to be the source of gas micronuclei from which bubbles evolved during decompression on smooth hydrophobic, but not hydrophilic, silicon wafers.
Hills (1992) showed that the inner surface of blood cavities such as the umbilical vein, right ventricle, pulmonary vein, and left ventricle are hydrophobic. He also demonstrated an oligolamellar lining of phospholipids on the luminal aspect of many blood vessels in the sheep, in venules and capillaries of the cerebral cortex and the aortic endothelium. These surfaces may be the site where nanobubbles and gas micronuclei form spontaneously. In a study of the effect of solutions on nanobubble production, Mazumder and Bhushan (2011) showed that saline, alkalinity and roughness each increased the density of nanobubbles compared with a smooth surface and pure water. We therefore suggest that the hydrophobic inner surface of blood vessels, which has a certain measure of roughness and in the living animal is bathed by alkaline and saline plasma, may be the site of nanobubble production and thus also of gas micronuclei and bubbles on decompression. For the experimental model, we chose large blood vessels from the sheep, some of which were shown by Hills (1992) to be hydrophobic.
Section snippets
Tissue preparation
The complete heart and lungs from six slaughtered sheep were obtained at the abattoir, and on removal intact from the thoracic cavity were immediately immersed in a cooler filled with saline. In the laboratory, under saline and without any exposure to air, samples (area 6 ± 2 cm2, mean ± SD) from the right and left atria, pulmonary artery and vein, aorta and superior vena cava, were gently stretched on microscope slides using metal clips and with the luminal aspect exposed. The six slides were
Contact angles
Contact angle should be measured on a flat, dry, horizontal surface. Although care was taken to approximate to these conditions, they were not always as perfect as they should have been. A small deviation may be expected in the measured angles due to unevenness and the slightly off-horizontal state of the luminal aspect of blood vessels. The blotting paper did not leave the tissues perfectly dry, and so the angle we measured was actually lower than would have been measured on an absolutely dry
Discussion
In contrast to other proposed mechanisms for the nucleation of gas micronuclei and their stabilisation, the process of nanobubble formation on a flat hydrophobic surface comprises both nucleation and stabilisation at the same time and location. Our two previous studies (Arieli and Marmur, 2011, Arieli and Marmur, 2013) proved that in supersaturated water, the nanobubbles formed on a flat hydrophobic silicon wafer gave rise to gas micronuclei and the growth of bubbles. In the present experiment,
Conclusion
Gas micronuclei are present on the flat hydrophobic luminal surface of ovine large blood vessels: the pulmonary artery and vein, the right and left atria, the aorta, and the superior vena cava. After decompression of the blood vessels, which had not been exposed to air beforehand, tiny bubbles were seen to rise from the luminal surface of both venous and arterial sites.
Acknowledgements
The authors thank Mr. R. Lincoln for skilful editing of the manuscript. This study was supported in part by a grant from the IDF Medical Corps and the Israel MOD.
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