Effect of Gas Type and Its Pressure on Nanobubble Generation

Modifications of Nanobubble Therapy for Cancer Treatment

Cancer development is related to genetic mutations in primary cells, where 5-10% of all cancers are derived from acquired genetic defects, most of which are a consequence of the environment and lifestyle. As it turns out, over half of cancer deaths are due to the generation of drug resistance. The local delivery of chemotherapeutic drugs may reduce their toxicity by increasing their therapeutic dose at targeted sites and by decreasing the plasma levels of circulating drugs. Nanobubbles have attracted much attention as an effective drug distribution system due to their non-invasiveness and targetability. This review aims to present the characteristics of nanobubble systems and their efficacy within the biomedical field with special emphasis on cancer treatment. In vivo and in vitro studies on cancer confirm nanobubbles' ability and good blood capillary perfusion; however, there is a need to define their safety and side effects in clinical trials.

Bulk Nanobubbles through Gas Supersaturation Originated by Hot and Cold Solvent Mixing

The nucleation mechanism of bulk nanobubbles remains unclear despite the considerable attention they have received in recent years. We propose two hypotheses: (i) The gas supersaturation in the bulk liquid is the primary factor for nanobubble nucleation, and (ii) the mixing of the same solvent at varying gas solubilities should produce nanobubbles, provided that the first hypothesis is correct. To test this hypothesis, we performed extensive experiments on nanobubble nucleation in both water and organic solvents. The temperature difference between hot and cold samples ranged from 10 to 80 °C in pure solvents such as water, methanol, ethanol, propanol, and butanol prepared and mixed in equal proportions. To the best of our knowledge, we report bulk nanobubble nucleation by mixing hot and cold solvents for the first time. The refractive index value calculations using Mie scattering theory confirmed the existence of nanobubbles. When surface tension dominates over surface charge, the critical work for nanobubble formation is ΔFc ∝ 1/ξ2, and when surface charge dominates over surface tension, the critical work is ΔFc ∝ ξ1/4. Our experimental results verify such dependency by measuring nanobubbles nucleated with varying degrees of gas supersaturation.

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

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.

Aeration and dissolution behavior of oxygen nanobubbles in water

HYPOTHESIS

Nanobubbles (NBs) in water elicit unique physicochemical and colloidal properties (e.g., high stability and longevity). Aeration kinetics and dissolution behavior of oxygen (O₂) NBs are assumed to be bubble size dependent.

EXPERIMENTS

As an indicator for aeration efficiency, volumetric mass transfer coefficient (K_L·a) was assessed by measuring the dissolved oxygen (DO) levels during aeration using O₂ NBs with different sizes. Mass transfer coefficient (K_L) was estimated by correlation analysis. Moreover, a modified Epstein-Plesset (EP) model was developed to predict the dissolution behavior by monitoring the DO and size changes during the dissolution of O₂ NBs in water.

FINDINGS

A higher rate of DO increase and a higher equilibrium DO level were both observed after aeration with NBs that present higher surface areas for the mass transfer of O₂ and a higher vapor pressure of O₂ to drive the partitioning equilibrium. Dissolution kinetics of O₂ NBs were highly dependent on the initial bubble size as indicated by the changes of bubble size and DO. Smaller NBs raised up DO faster, whereas larger NBs could lead to higher equilibrium DO levels. Moreover, the rate of DO decline and the quasi-steady DO levels both decreased when the dilution ratio increased, confirming that O₂ NBs dictates the DO level in water. Finally, the dissolving NBs may either swell or shrink according to the model prediction.

Laser Fluorescence and Extinction Methods for Measuring the Flow and Composition of Milk in a Milking Machine

Automation of milking systems is linked to accurate measurement of fluctuations in milk flow during milking. To assess the fluctuations of the milk flow, the formation and movement of milk portions in the milking machine-milk pipeline system was studied. By considering the movement of a milk plug along the milk pipeline, a hydraulic model of the formation of a critical volume of milk in the milking machine manifold was compiled. In practice, the most expedient way of determining milk flow parameters may be to measure the laser fluorescent and extinction responses of moving air-milk mixture. We have implemented a new laser sensing method for measuring the flow rate and composition of milk on the basis of counting the optical response pulses received from moving dispersed components by a CCD array or a randomized fiber optic bundle. Using the developed laser sensors, the theoretical model of milk flow was tested.

Long-Term Effect of Low-Frequency Electromagnetic Irradiation in Water and Isotonic Aqueous Solutions as Studied by Photoluminescence from Polymer Membrane

The swelling of a polymer membrane Nafion^TM in deionized water and isotonic NaCl and Ringer’s solutions was studied by photoluminescent spectroscopy. According to our previous studies, the surface of this membrane could be considered as a model for a cellular surface. Liquid samples, in which the membrane was soaked, were subjected to preliminary electromagnetic treatment, which consisted of irradiating these samples with electric rectangular pulses of 1 µs duration using platinum electrodes immersed in the liquid. We used a series of pulses with a repetition rate of 11–125 Hz; the pulse amplitudes were equal to 100 and 500 mV. It turned out that at certain pulse repetition rates and their amplitudes, the characteristic swelling time of the polymer membrane significantly differs from the swelling time in untreated (reference) samples. At the same time, there is no effect for certain frequencies/pulse amplitudes. The time interval between electromagnetic treatment and measurements was about 20 min. Thus, in our experiments the effects associated with the long-term relaxation of liquids on the electromagnetic processing are manifested. The effect of long-term relaxation could be associated with a slight change in the geometric characteristics of bubston clusters during electromagnetic treatment.