Method for controlling generation of active radicals by cold plasma jet at atmospheric pressure for biomedical applications

Abstract

FIELD: plasma medicine.SUBSTANCE: invention relates to the field of electrical gas-discharge devices and low-temperature plasma sources, in particular to plasma medicine, namely to methods and devices for generating a cold plasma jet of atmospheric pressure, intended for controlled exposure of biological objects to active plasma components. A method for controlling the generation of active radicals by a cold plasma jet at atmospheric pressure for biomedical applications includes the formation of a plasma jet in a gas-discharge device with coaxial electrode geometry while pumping a plasma-forming gas, feeding the plasma-forming gas into a gas-discharge cell, igniting a gas discharge in it, and forming a cold plasma jet. The intensity of generation of active radicals, primarily hydroxyl radicals OH, is controlled by: a) regulating the repetition rate of current pulses reaching the biological object in relation to the frequency of the applied voltage by changing the parameters and shape of the initiating voltage; b) introducing a control electrode under zero or floating potential into the gap between the nozzle of the gas discharge device and the biological object; c) controlling the humidity of the environment in the zone of action of the plasma jet in the range of relative humidity of 20-90%.EFFECT: ability to carry out controlled and reproducible generation of active radicals, primarily the hydroxyl radical OH, which allows for targeted changes in the intensity of plasma-chemical action on a biological object.6 cl, 19 dwg

Description

[0001] The invention relates to medical technology and plasma medicine, specifically to methods and devices for generating a cold (low-temperature) plasma jet at atmospheric pressure, designed for the controlled exposure of biological objects to active plasma components, primarily reactive oxygen and nitrogen species, and can be used for antitumor therapy, antimicrobial treatment, stimulation of tissue regeneration, and other biomedical applications. The invention also relates to the field of electric gas-discharge devices and low-temperature plasma sources.

[0002] It is known that a cold atmospheric-pressure plasma jet is a set of streamer discharges propagating in a plasma-forming gas flow and is capable of delivering electric fields, high-energy electrons, and active chemical species to the irradiated object without significant thermal impact. The effect of cold plasma on biological objects is due to the generation of reactive oxygen and nitrogen species, including the hydroxyl radical OH, hydrogen peroxide H₂O₂, ozone O₃, superoxide anion O₂⁻, peroxynitrite ONOO⁻, and others, which play a key role in the induction of oxidative stress and programmed tumor cell death.

[0003] Technology Level

[0004] The effect of a low-temperature plasma jet on biological objects consists of generating and transporting charged particles to the plasma-target interface, generating large electric fields at the plasma-target interface, and stimulating chemical reactions in the gas phase and in the liquid above and within the target. The main chemical reactants are various active forms of oxygen, such as hydroxide OH, hydrogen peroxide H2O2, and singlet oxygen. 1 O2, ozone O3, superoxide radical anion O2 - etc., various active forms of nitrogen, such as peroxynitrite ONOO - , nitrogen dioxide NO2 * , nitrite (NO2 - ) and nitrate (NO3 -), ions, etc. [Kalghatgi S. Effects of Non-Thermal Plasma on Mammalian Cells / S. Kalghatgi, CM Kelly, E. Cerchar, B. Torabi, O. Alekseev, A. Fridman, G. Friedman, J. Azizkhan-Clifford / / J. PloSone. - 2011. Vol. 6. - P. e16270]. Oxygen-nitrogen-containing radicals, as well as ions, actively affect the processes in biological cells. The role of increased intracellular content of active oxygen species in anticancer therapy using a cold plasma jet has been confirmed by studies. It has been experimentally shown that after plasma treatment of biological objects in cells, including cancer cells, a significant increase in the concentration of active oxygen species is observed [Yan D. Toward understanding the selective anticancer capacity of cold atmospheric plasma-A model based on aquaporins (Review) / / Biointerphases. - 2015. Vol. 10. No. 4. - P. 040801], while at present their chemical composition in cells after plasma treatment remains unknown.However, it is suggested that OH, H2O2 and O2 are the main radicals responsible for the elevated levels of reactive oxygen species in cold plasma jet-treated cells.

[0005] It has been shown that the effectiveness of cold plasma jet exposure on the rate of cancer cell division drops significantly if the cancer cells were pre-treated with intracellular reactive oxygen species acceptors [Ahn HJ Atmospheric-Pressure Plasma Jet Induces Apoptosis Involving Mitochondria via Generation of Free Radicals / HJ Ahn, KI Kim, G. Kim, E. Moon, SS Yang, J.-S. Lee / / PloSone. 2011; 6(11): e28154]. Therefore, increasing the rate of generation of active particles, in particular OH, is a way to intensify the processes of exposure of cold plasma jet to biological objects.

[0006] A low-temperature plasma jet source is known [Sarani A. Atmospheric pressure plasma jet in Ar and Ar / H2O mixtures: Optical emission spectroscopy and temperature measurements / A. Sarani, A.Yu. Nikiforov, Ch. Leys / / Physics of Plasmas. - 2010. Vol.17. - P.063504], containing a cylindrical housing with an internal diameter of 1.3 mm, made with the possibility of filling and pumping through it with a working gas at a rate of 0.695 to 4.82 l / min, as well as with the possibility of forming in it a discharge region between an internal central high-voltage electrode in the form of a rod with a diameter of 0.5 mm, placed in the said housing and an external high-voltage electrode, made, accordingly, in the form of a shell enclosing the cylindrical housing from the outside. The electrodes form a discharge gap and are positioned at a distance from each other that ensures the formation of a discharge structure. The electrodes are equipped with electrical terminals at their ends.Argon and / or a mixture of argon with added water vapor (0.05-0.67%) were used as the working gas. Application of a sinusoidal voltage with a frequency of 71 kHz and an amplitude voltage of 12.2-17 kV leads to the appearance of a plasma jet. The presence of OH radicals is recorded in the emission spectra of the plasma jet, and the intensity in the plasma generated in the Ar+0.05% H2O mixture shows a higher intensity of OH radicals in the emission spectra than in pure argon. However, the gas temperature increases with the addition of water to the supplied gas from 620°K in pure Ar to 1130°K for the Ar+0.76% H2O mixture, which makes it unsuitable for exposure to biological objects, limited by a temperature of up to 40°C (313°K). A disadvantage of the source is the inability to control the composition and concentration of active radicals in the area of ​​interaction of the low-temperature plasma jet with the object.

[0007] A cold plasma jet source is known [Y. Krasik, J. Felsteiner, Y. Slutsker, Z. Gil, J. Cohen, Y. Binen-Baum. Cold plasma generating system. United States Patent Application Publication, US 2017 / 0354453A1. 2017 Dec. 14], comprising a cylindrical housing with an inner diameter of 2 mm, configured to be filled and pumped through with a working gas, as well as with the possibility of forming a discharge region in it between an internal high-voltage electrode placed in said housing, made in the form of a shell, wherein its outer diameter is equal to the inner diameter of the housing, and the inner diameter is 1 mm, and an external grounded electrode, made, accordingly, in the form of a shell encircling the cylindrical housing from the outside. The electrodes form a discharge gap and are installed at a distance relative to each other, ensuring the formation of a discharge structure. The electrodes are provided with electrical terminals at their ends.Neon and argon mixtures in ratios of 98:2 and 99:1, or helium, nitrogen, and / or oxygen mixtures, were used as the working gas. High-frequency pulses with a frequency of approximately 0.5-10 MHz and a voltage amplitude of 0.5-6 kV were used. The generated plasma was characterized by a gas temperature of approximately 40°C (or usually between 25 and 50°C). A disadvantage of this source is the inability to regulate the composition and concentration of active radicals generated by the plasma in the surrounding space, in the region of interaction with the object.

[0008] The following sources of cold plasma jets of atmospheric pressure are known, in which the generation of active radicals is carried out by changing the composition of the plasma-forming gas or by increasing the discharge power.

[0009] Invention US10121638 "Atmospheric-pressure plasma jet generating device" is known. It is a device for generating a non-thermal atmospheric plasma jet suitable for sterilization, wound healing, and other biomedical applications. Priority date: 08-06-2018, copyright holder: National Yang Ming Chiao Tung University, NYCU. The device includes a housing, a discharge tube, an air inlet, and an air vent. The air inlet is connected to the air vent and the discharge tube. The discharge tube includes an inner electrode, a first dielectric material, and an outer electrode. The first dielectric material is located between the outer and inner electrodes, and there are channels between the inner electrode and the first dielectric tube. An external power source is electrically connected to the inner and outer electrodes to generate a high electric field inside the discharge tube.As the working gas flows through the discharge tube via the air inlet, plasma is generated by a high electric field and then exits through the air vent. The present invention enables the generation of a non-thermal, atmospheric-pressure plasma jet for biomedical applications.

[0010] Invention US9693441, "Method for generating an atmospheric plasma jet and atmospheric plasma minitorch device", priority 2014-11-14, copyright holder NADIR SRL, Padua (IT) - "Method for generating an atmospheric plasma jet and device for creating an atmospheric plasma mini-torch". This work describes a method and device for generating plasma under conditions of atmospheric pressure and low temperature. The described device for generating plasma includes a first pair of electrodes, each of which is separated by a dielectric layer and is located outside relative to a tubular channel through which gas flows, and a second pair of electrodes, also in this case, each of which is separated by a dielectric layer and is located outside relative to the said tubular channel through which the same gas flows, directed downstream relative to the first pair. High-frequency excitation is applied to the first pair of electrodes, and radio-frequency excitation is applied to the second pair of electrodes.The plasma generated in this manner exits the gas flow at the exit of the transport channel. High-frequency excitation can be applied in pulse sequences, and the radiofrequency generator is significantly activated during these pulse sequences to limit the thermal load on the substrate being processed. Chemical precursors and reagents can be added to the plasma as vapors or aerosols via a central transport channel located coaxially with the tubular gas channel.

[0011] Invention US20140378892A1 “System And Method For Cold Plasma Therapy” is known, priority 2014-11-14, copyright holders: M. Keidar, C. Guron; B. Trink, Alexey Shashurin, - “System and method for using cold plasma to treat tumor tissue with a working gas supply and an electrode system”. The device uses cold plasma to treat cancer tumors. The device has a gas supply tube with an outlet end. The gas supply tube is designed to supply gas to the outlet end. A syringe with an opening is provided. The syringe is connected to the supply tube and is designed to supply gas to the opening. The first electrode is located inside the syringe, and the second electrode is located near the opening. The first and second electrodes excite the gas, converting it to a state of cold plasma before it is withdrawn from the syringe opening. An endoscopic tube can be used instead of a syringe.To remove gas that has entered the body cavity under the action of the cold plasma jet, an outlet tube may be provided.

[0012] Publication EP0968524A1, “Atmospheric-pressure plasma jet,” assigned to Univ. California [US]; Selwyn Gary S., priority date 2000-01-05, describes a gamma-ray plasma discharge with a resonant cavity that can operate at atmospheric pressure and near room temperature using 13.56 MHz radio frequency (RF) power. Unlike plasma torches, the discharge produces a gaseous stream with a temperature no higher than 250°C with an applied power of about 300 W and exhibits distinct non-thermal characteristics. The simplest design uses two concentric cylindrical electrodes to generate plasma in the annular region between them. A “jet” of long-lived metastable and reactive particles is generated, capable of rapidly cleaning or etching metals and other materials, extending over 8 inches beyond the open end of the electrodes.The device prevents arcing by using gas mixtures containing helium, which limits ionization, high flow rates, and a properly shaped electrode powered by RF radiation. Operating at atmospheric pressure prevents ions from remaining far enough outside the active plasma discharge to bombard the workpiece, unlike low-pressure and conventional plasma sources.

[0013] The above patents US10121638B1, US9693441B2, US20140378892A1 and EP0968524A4 are analogs, as they describe atmospheric plasma jets, cold plasma generation and biomedical applications.

[0014] Invention US9067273 is known - "High Density Atmospheric Plasma Jet Devices by Jet-to-Jet Interaction", the copyright holder is Clemson University (Clemson, SC), priority date is May 14, 2013, which describes a device with multiple plasma jets and their interaction to form a dense plasma beam (possible applications - materials processing, sterilization, medicine). A device for creating a plasma jet at atmospheric pressure is described, intended for use in various fields of application. The described system may include a tube array consisting of a plurality of individual tubes arranged in a honeycomb structure. By varying the linear velocity of the gas source of the system, it is possible to create multiple non-thermal atmospheric plasma jets that interact in such a way that they form a single plasma jet, as opposed to multiple collimated plasma jets.A single jet formed by the interaction of multiple tubes can exhibit enhanced optical intensity and energy compared to a plasma jet emitted from a single tube or well-collimated plasma jets emitted from multiple tubes.

[0015] Cold Plasma Medical Technologies, Inc.'s patents and invention applications (US20130072858, US20130072860, US20130072861, etc.) describe cold plasma devices for medical use with pulsed power supply, DBD structures, and plasma delivery kits for patients, demonstrating a variety of delivery methods and electrode configurations for generating cold plasma for therapeutic purposes.

[0016] For example, the invention "Cold plasma treatment devices and associated methods" US8928230, priority date 14-09-2012, owner Watson Gregory A; Jacofsky Marc C; Cold Plasma Medical Technologies Inc. describes a cold plasma treatment device designed to deliver cold plasma to a patient's treatment area. Gas is supplied to a gas compartment, where it is activated by an electrode connected to a pulse source to generate cold plasma. A dielectric barrier is located between the gas compartment and the electrode, forming a dielectric barrier discharge device. Cold plasma exits the gas compartment through a lower element with multiple openings. Noble gases, such as helium, or combinations of noble gases can be used as gases.

[0017] Invention application US20140188037, "Method and Apparatus for Cold Plasma Bromhidrosis Treatment," priority date December 31, 2013, owned by Cold Plasma Medical Technologies, Inc., describes a device for treating bromhidrosis with cold plasma. The dielectric barrier discharge device consists of an electrode located near the dielectric barrier, which is designed to expose the surface to cold plasma. The electrode is connected to a pulsed high-voltage cold plasma power source, which can be external or internal to the housing containing the dielectric barrier discharge device. The device for treating bromhidrosis with cold plasma can be powered by batteries or an AC / DC adapter.

[0018] Utility model RU202393U1 "Device for generating a non-thermal plasma flow", priority dated 2020-03-12, copyright holder - Immanuel Kant Baltic Federal University, describes a flow of atmospheric pressure plasma. The utility model is intended for generating non-thermal gas-discharge plasma flows, which can be used for the non-drug treatment of septic wounds, in dentistry (treatment of periodontal disease, disinfection of dental canals, teeth whitening), in dermatology (non-drug treatment of acne, eczema, various forms of dermatitis), in cosmetology (non-invasive plasma lifting, post-operative rehabilitation). The technical result is increased reliability and simplification of the design. The device for generating a non-thermal plasma flow comprises a high-voltage power source, a nozzle with an electrode system, a device for pumping working gas through the nozzle.Unlike the prototype, voltage is supplied to the electrodes in the form of pulses with a duration of 2 μs and pauses between pulses with a duration of 200 μs, which eliminates contraction of the gas discharge at a low pumping speed of the working gas and a decrease in the gas temperature of the jet.

[0019] Invention application WO2021133232A1 - "Device and Method for Generating Low-Temperature Plasma", copyright holder - A.V. Khinkis, priority dated 2020-12-25, describes a method and device for generating highly nonequilibrium low-temperature plasma of pulsed gas discharges at atmospheric and reduced pressure, comprising a solid-state pulse generator with a current sensor, a discharge oscillatory circuit receiving energy from said generator, as well as a control computer device for regulating the energy input into the discharge circuit in the form of short pulses by independently and dynamically adjusting the frequency and duty cycle of the power pulses supplied to the load through the shock excitation circuit based on the data received via feedback from said current sensors. The energy input is regulated in such a way as to constantly maintain stable plasma parameters.The technical result consists in the possibility of controlling the properties of the environment in the processing zone with reduced energy consumption.

[0020] The publications (MDPI open access journals / academic articles on tiny plasma jet) contain descriptions of devices and methods, research on the generation of cold plasma jet and active ROS / RNS for biomedical purposes.

[0021] For example, the article by Zhitong Chen, Richard Obenchain, Richard E. Wirz. Tiny Cold Atmospheric Plasma Jet for Biomedical Applications / / Processes 2021, 9(2), 249; https: / / doi.org / 10.3390 / pr9020249 shows that traditional plasma jets for biomedical applications generally have several disadvantages, such as high voltage, large volume of supplied gas, large volume of plasma probe, and discharge formation inside the organ. Therefore, the use of these jets inside a living organism is a challenging task. The authors developed a miniature plasma jet with a single electrode and evaluated its application in clinical biomedical applications. They investigated the effects of input voltage and flow rate on the jet length and studied the physical parameters of the plasma jet, including discharge voltage, average gas and object temperature, and optical radiation.The interaction of a miniature plasma jet with five objects (deionized water, metal, cardboard, pork belly, and pork muscle) was studied at distances of 10 mm and 15 mm from the jet nozzle. The results showed that the miniature plasma jet did not cause tissue damage or burns, while the intensity of reactive oxygen / nitrogen species increased as the distance decreased from 15 mm to 10 mm. These preliminary observations suggest that a miniature plasma jet device could be a potentially useful tool in clinical biomedical applications.

[0022] The common disadvantages of the above known solutions are:

[0023] lack of direct control over the concentration of active radicals in the affected area;

[0024] temperature increase when adding water vapor;

[0025] stochastic nature of discharge processes;

[0026] the need to use additional high-voltage power sources to implement the method;

[0027] The closest analogue is "Method for Exposing a Biological Object to a Cold Plasma Jet and an Installation for its Implementation," Russian Patent No. 2764619, application date: 23.12.2020, patent holders: ISP SB RAS, ITAM SB RAS, in which radical generation is controlled by auxiliary electrodes under high potential. The method involves pumping a working gas through a dielectric channel through a plasma jet generator, supplied to the channel through an inlet. A gas discharge is ignited in the channel by electrodes forming a discharge structure. A high-voltage sinusoidal voltage is applied to the electrodes, ensuring the discharge and formation of plasma, and obtaining a plasma jet flowing out of the channel outlet. The plasma jet is directed at the object. The object is exposed to active forms - radicals and / or ions generated as a result of the gas discharge.In the spatial gap containing the escaping plasma jet and the target, an electric field is generated with the ability to change the distribution of the existing electric field in a direction parallel to the jet's propagation. By changing the electric field distribution in the spatial gap, the electron energy distribution is controlled. The setup comprises a working gas supply system, a high-voltage power source, and a plasma jet generator with a dielectric tubular housing with an internal volume containing a channel for pumping the working gas, igniting a gas discharge, and forming plasma. The channel communicates with the working gas supply system through an inlet in the housing. The plasma jet generator is equipped with a discharge structure consisting of high-voltage discharge electrodes electrically connected to the high-voltage power source to form a discharge circuit.One electrode is located outside the housing, with the option of encircling it, while the other electrode is located within the housing's interior. The apparatus is equipped with an auxiliary electrode, which is brought into contact with the target and positioned at the required distance from the plasma jet outlet, defining the spatial gap in which the escaping plasma jet and the target are located. Furthermore, the apparatus may be equipped with a pair of auxiliary electrodes, one of which, as noted, is brought into contact with the target and positioned at a distance from the outlet, defining the specified gap, while the second encircles the plasma jet, ensuring its passage through it without interacting with it, while maintaining the effectiveness of the potential applied to it with respect to the electric field of the gap.This achieves control over the quantitative content of active forms (radicals, ions, radicals and / or ions) in a cold plasma jet, control over the distribution of active forms along the length of the jet, and control over the composition of active forms that have a dominant effect on the object.

[0028] The disadvantages of the analogue are:

[0029] The method of initiating a plasma jet with a sinusoidal voltage is characterized by irregularity in the current pulses reaching the irradiated objects, which leads to an uncontrolled change in the temperature of the biological object with the possible excess of the maximum permissible value; stochastic changes in the generation of active radicals, the level of which depends on the current magnitude; additional high-voltage power sources are required to power the auxiliary electrodes.

[0030] The objective of the presented invention is to create a method that ensures controlled and reproducible generation of active radicals, primarily the hydroxyl radical OH, which is not accompanied by an uncontrolled increase in the temperature of a biological object and allows for a targeted change in the intensity of the plasma-chemical effect on a biological object.

[0031] The stated problem is solved in that in the claimed method, which consists of generating a cold plasma jet in a gas-discharge device during pumping of a plasma-forming gas and the action of the plasma jet on a biological object, the generation of a plasma jet is carried out by sinusoidal or pulsed initiation, the supply of plasma-forming gas into a gas-discharge cell is carried out, the ignition of a gas discharge in it by supplying an initiating voltage to the internal and external discharge electrodes, the formation of a cold plasma jet, spreading beyond the gas-discharge cell, and the action of said plasma jet on a biological object located on an auxiliary electrode.

[0032] During pulsed initiation of a plasma jet, the initiating voltage is generated in the form of unipolar pulses with a repetition frequency from 1 to 30 kHz and an adjustable duration from 6 to 20 μs; the duration of the voltage pulses initiating the streamer discharge is regulated; the change in the frequency and amplitude of the current at the surface of the biological object when exposed to it and the change in the distribution of the electric field in the gap between the plasma jet generator nozzle and the biological object are achieved by introducing a control electrode located in the plasma jet propagation zone and under a floating potential; the ambient humidity in the plasma jet impact zone is maintained in the range of 20-90%.

[0033] Reducing the pulse duration leads to an increase in the amplitude of the current pulses and the pulse power of the streamers, which, in turn, leads to an increase in the rate of plasma-chemical reactions of generating hydroxyl radicals OH from water molecules in the gas phase and on the surface of a biological object.

[0034] During pulsed initiation of the plasma jet, the intensity of active radical generation is controlled by a control electrode located at a certain distance from the jet generator nozzle (half the distance between the nozzle and the irradiated object, which is located on the auxiliary electrode) perpendicular to the direction of propagation of the plasma jet and having an opening larger than the transverse dimension of the plasma jet, during pulsed initiation of the plasma jet.

[0035] The generation of active radicals is controlled by a targeted change in the ratio between the frequency of the initiating voltage and the frequency of the current reaching the biological object, wherein the frequency of the current in the zone of interaction of the plasma jet with the biological object is set to be at least two times lower than the frequency of the initiating voltage, which leads to an increase in the amplitude of the current pulses and the pulse power of the plasma jet streamers and, as a consequence, to an intensification of the generation of active radicals, primarily hydroxyl radicals OH, in the zone of impact on the biological object.

[0036] In this case, the current frequency in the plasma jet interaction zone with the biological object may be 2 or 4 times lower than the initiating voltage frequency. The current frequency can be scaled down relative to the initiating voltage frequency without changing the plasma-forming gas composition, by varying the frequency or amplitude of the initiating voltage, or by reducing the duration of the initiating voltage pulse, with the gas-discharge cell geometry unchanged, or by using a control electrode located in the plasma jet propagation zone and under a floating potential.

[0037] Streamers are formed with each voltage pulse, but typically only a portion of them reach the target surface. This means that the operating voltage frequency can be significantly higher than the frequency of the streamers' impact on the biological object, which determines the effectiveness of the impact. Increasing the streamer's impact frequency to the frequency of the initiating voltage is accomplished by reducing the duration of the initiating voltage pulse. Thus, an increase in the integral pulse power of the streamers during impact on the biological object is achieved without increasing the average discharge power, which ensures that the plasma jet temperature remains low.

[0038] The intensification of the generation of hydroxyl radicals OH is confirmed by an increase in the intensity of the spectral line of OH emission with a wavelength of λ ≈ 309 nm (transition A 2 ∑ + - X 2(P). The gas flow rates pumped through the gas discharge cell range from 7 l / min to 9 l / min. This range is determined by two competing physical factors. At flow rates below 7 l / min, the concentration of air molecules (the source of H2O molecules) in the plasma jet combustion zone increases, but the rate of removal of atomic and molecular discharge products from the active zone is insufficient: intermediate products recombine in the nozzle-object gap, without reaching the biological object. At flow rates above 9 l / min, the excess gas-dynamic helium flow displaces atmospheric air from the interaction zone, reducing the available H2O vapor concentration and thereby decreasing the yield of hydroxyl radicals (OH). In the range of 7-9 l / min, a qualitative maximum of the intensity of the OH spectral line (λ≈ 309 nm) is achieved, exceeding the values ​​at 6 l / min and 12 l / min by at least 30-40% (Fig. 12), which indicates a threshold, rather than smooth, nature of the dependence.

[0039] With sinusoidal plasma jet initiation, the voltage at the discharge electrodes is generated as a sinusoidal voltage with a frequency of 10 to 60 kHz. The current frequency in the plasma jet's impact zone on the biological object is set in the range of 10 to 15 kHz.

[0040] In this case, an additional electrode can be used, covering the gas discharge cell (located on the outer side of the dielectric housing), which is under a floating potential and provides a change in the frequency of the current contact in the zone of action of the plasma jet on the biological object during sinusoidal initiation of the plasma jet; it is not used during pulsed initiation of the plasma jet.

[0041] The plasma jet is applied under conditions of controlled ambient humidity in the exposure zone, at a relative humidity of 20 to 90%, while an increase in humidity enhances the effect of intensifying the generation of hydroxyl radicals OH at a given ratio of the current frequency and the frequency of the initiating voltage.

[0042] To implement the method, an installation is used that contains a gas-discharge cell, which consists of a dielectric cylindrical (or tubular) body with an opening for supplying working gas, an internal metal electrode, which can be made in the form of a tube with an internal channel, an external metal electrode enclosing the gas-discharge cell and located on the outer side of the dielectric body, a dielectric sleeve with a capillary opening, acting as a nozzle, an insulator, a gas distribution system; a high-voltage power source; an auxiliary electrode for placing a biological object, while it can contain an additional, control or mesh electrodes.

[0043] An additional electrode enclosing the gas discharge cell (located on the outer side of the dielectric housing), which is under a floating potential and provides a change in the frequency of the current contact in the zone of action of the plasma jet on the biological object during sinusoidal initiation of the plasma jet; it was not used during pulsed initiation of the plasma jet.

[0044] Control electrode - an electrode located at some distance from the jet generator nozzle (1 / 2 the distance between the nozzle and the irradiated object, which is located on the auxiliary electrode), perpendicular to the direction of propagation of the plasma jet and having an opening larger than the transverse size of the plasma jet; allows controlling the intensity of the generation of active radicals during pulsed and sinusoidal initiation of the plasma jet and ensures a change in the frequency of contact of the current in the zone of action of the plasma jet on the biological object during sinusoidal initiation of voltage, with a diameter of at least 16 mm with a round opening of 12 mm in diameter.

[0045] A variant of the control electrode design is that it is made in the form of a metal mesh cylinder (cell size no more than 2 mm) with an internal diameter exceeding the transverse size of the plasma jet by at least 2 mm, a height of 8-15 mm, located between the generator nozzle and the biological object, under zero or floating potential, providing an increase in the intensity of the OH line radiation (λ ≈ 309 nm) by at least 2-2.5 times.

[0046] The proposed invention differs from its analogues in that targeted control of the generation of active radicals is carried out without the introduction of additional high-voltage sources, by controlling the frequency of current contact, the duration of pulses, the humidity of the environment and the configuration of the electric field using at least one additional electrode with zero or floating potential.

[0047] Also distinctive features of the method are the use of the frequency of the current reaching the object as a control parameter, division of the current frequency relative to the voltage frequency, an increase in the pulse power of streamers without increasing the average power, control of plasma chemistry without changing the composition of the gas, optical control of the radiation of the hydroxyl radical OH (λ ≈ 309 nm), the relationship of physical parameters with the biological effect.

[0048] To implement the method, a device is used, the distinctive features of which are three types of electrodes under floating or zero potential.

[0049] The drawings show the results of the implementation of the proposed method for controlling the generation of active radicals by a cold plasma jet of atmospheric pressure using an installation implementing the proposed method.

[0050] Fig. 1 - block diagram of a cold plasma jet generation installation implementing a method for controlling the generation of active radicals, containing a dielectric housing (1), an internal potential discharge metal electrode (2), an external discharge metal electrode (3), a dielectric sleeve with a capillary opening that acts as a nozzle (4), an insulator (5), an opening for supplying working gas (6), a gas distribution system (7), a high-voltage power source (8), a biological object (9), an auxiliary electrode (10).

[0051] Fig. 2 - a variant of the installation in which the supply of working gas is carried out through an internal potential discharge electrode, made in the form of a tube with an internal channel.

[0052] Fig. 3 - a variant of the installation with an additional electrode (11) covering the gas discharge cell and located under a floating potential, providing a change in the frequency and amplitude of the current at the surface of the biological object when exposed to a plasma jet.

[0053] Fig. 4-6 - oscillograms of the sinusoidal voltage supplied to the electrodes and the current recorded in the zone of interaction of the plasma jet with the biological object, illustrating the modes of equality of the current frequency to the voltage frequency, as well as the modes of dividing the current frequency by 2 and 4 times relative to the voltage frequency.

[0054] Fig. 7 - diagrams of the frequency modes of operation of the cold plasma jet generator, demonstrating the dependence of the current amplitude and pulse power of the discharge on the frequency of the applied voltage.

[0055] Fig. 8 - oscillograms of unipolar pulse voltage and current at different durations of initiating voltage pulses.

[0056] Fig. 9 - spectra of optical radiation in the zone of interaction of the plasma jet with a biological object at different pulse durations, demonstrating the enhancement of the spectral line of the hydroxyl radical OH (λ≈309 nm).

[0057] Fig. 10-12 - emission spectra of a plasma jet over a biological object at different values ​​of ambient humidity and working gas flow rate, illustrating the influence of humidity and gas flow rate on the intensity of OH radical generation.

[0058] Fig. 13 - embodiment of the installation with a control electrode (12) located perpendicular to the direction of propagation of the plasma jet and having an opening exceeding the transverse dimension of the plasma jet.

[0059] Fig. 14 - distribution of the radiation intensity of OH molecules between the nozzle and the object in the presence and absence of the control electrode (12).

[0060] Fig. 15 - installation option with a control electrode (13) made in the form of a metal mesh cylinder.

[0061] Fig. 16 - emission spectra of the hydroxyl radical OH in the absence of a control grid electrode (13) and in its presence with zero and floating potential.

[0062] Fig. 17-19 - Experimental data demonstrating the biological effectiveness of the method, including a decrease in the viability of tumor cells in vitro and a slowdown in tumor growth in vivo.

[0063] Description of Figs. 4-14, 16-19.

[0064] Fig. 4 shows oscillograms of a sinusoidal voltage with a frequency of 52 kHz applied to the electrodes to generate a plasma jet, and the current recorded in the area where the plasma jet touches the biological object, the frequency of which is 4 times lower than the frequency of the applied voltage. The distance to the biological object is 20 mm, and the flow rate of the working gas (helium) pumped through the gas discharge cell is 9 l / min.

[0065] Fig. 5 shows oscillograms of a sinusoidal voltage with a frequency of 26 kHz applied to the electrodes to generate a plasma jet, and the current recorded in the area where the plasma jet touches the biological object, the frequency of which is half the frequency of the applied voltage. The distance to the biological object is 20 mm, and the flow rate of the working gas (helium) pumped through the gas discharge cell is 9 l / min.

[0066] Fig. 6 shows oscillograms of a sinusoidal voltage with a frequency of 13 kHz applied to the electrodes to generate a plasma jet, and the current recorded in the area where the plasma jet touches the biological object, the frequency of which is equal to the frequency of the applied voltage. The distance to the biological object is 20 mm, and the flow rate of the working gas (helium) pumped through the gas discharge cell is 9 l / min.

[0067] Fig. 7 shows the diagrams of the frequency modes of operation of the cold plasma jet generator, demonstrating the change in the current amplitude in the interaction zone with the irradiated object at different frequencies of the applied sinusoidal voltage. The nature of the change in the current frequency in the area of ​​action on the biological object is shown depending on the frequency of the applied voltage at a fixed voltage amplitude of 3.5; 4.3; 5.2 kV, where 1 is the range in which the current frequency is equal to the frequency of the applied voltage, 2 is the range where the current frequency is 2 times less than the frequency of the applied voltage, 3 is the range where the current frequency is 4 times less than the frequency of the applied voltage.

[0068] Fig. 8 shows oscillograms of a unipolar pulsed voltage initiating a plasma jet with a frequency of 30 kHz, applied to the internal potential discharge electrode to generate a plasma jet and current pulses recorded in the area of ​​contact of the plasma jet with a biological object at a voltage pulse duration of 7 and 15 μs.

[0069] Figure 9 shows a fragment of the emission spectrum of the region of interaction between a plasma jet and a biological object located in a culture fluid at pulse durations of 7 μs (curve 1) and 15 μs (curve 2). With a decrease in the duration of the applied voltage pulses, a significant strengthening of the hydroxyl radical OH line above the surface of the biological object is observed. The intensity ratio of the OH lines, with all other things being equal, can exceed 3 in the case of shortening the pulse duration.

[0070] Figure 10 shows a fragment of the plasma jet emission spectrum above a biological object located in a culture fluid. Artificially increasing the water vapor concentration (humidity) in the affected area from 30% (curve 1) to 60% (curve 2) and 90% (curve 3) leads to an intensification of the generation of active radicals. In particular, the intensity of the spectral line of the hydroxyl radical OH (λ≈309 nm) at 90% humidity (curve 3) is approximately 2 times higher than at 30% humidity (curve 1).

[0071] Fig. 11 shows a fragment of the emission spectrum of a cold plasma jet above a biological object located in a culture liquid, under conditions of increased humidity of the environment ~ 55%, at different amplitudes of the applied sinusoidal voltage of 5.6 kV (curve 1), 6 kV (curve 2), 6.2 kV (curve 3) and 6.6 kV (curve 4) with a frequency of 52 kHz, as well as a demonstration of a proportional increase in the intensity of the generation of the OH radical (λ≈309 nm) with an increase in the amplitude of the applied voltage.

[0072] Fig. 12 shows a fragment of the emission spectrum of a cold plasma jet above a biological object located in a culture liquid, under conditions of increased humidity of the environment ~55%, at different gas flow rates: 3 l / min (curve 1), 6 l / min (curve 2), 7.5 l / min (curve 3), 9 l / min (curve 4), 12 l / min (curve 5), pumped through the gas discharge cell. The intensity of the spectral line of the hydroxyl radical OH (λ≈309 nm) reaches its maximum value at a gas flow rate of 7-9 l / min and noticeably decreases both with a decrease in the flow rate to 6 l / min (curve 2, insufficient removal of recombination products) and with its increase to 12 l / min (curve 5, displacement of water vapor from the impact zone by a helium flow). Thus, the dependence of the intensity of OH generation on the flow rate has a nonlinear threshold character with a pronounced maximum in the range of 7-9 l / min.

[0073] Fig. 13 shows the implementation of the installation for generating a cold plasma jet with a control electrode device located perpendicular to the direction of propagation of the plasma jet at some distance from the nozzle of the jet generator, having an opening of an arbitrary shape with a size greater than the transverse size of the plasma jet, where 1 is a dielectric housing; 2 is an internal metal electrode; 3 is an external metal electrode; 4 is a dielectric sleeve with a capillary opening (nozzle); 5 is an insulator; 6 is an opening for supplying working gas; 7 is a gas distribution system; 8 is a high-voltage power source; 9 is an irradiated biological object; 10 is an auxiliary electrode; 12 is a control electrode.

[0074] Fig. 14 shows the distribution of the relative intensity of the radiation of excited OH molecules (λ≈309 nm) between the nozzle and the irradiated object in the absence (curve 1) and presence (curve 2) of a control electrode with zero potential.

[0075] Fig. 15 shows the implementation of the installation for generating a cold plasma jet with a mesh electrode device in the form of a metal mesh cylinder located between the nozzle of the jet generator and the biological object, having an internal diameter with a size greater than the transverse size of the plasma jet, where 1 is a dielectric body; 2 is an internal metal electrode; 3 is an external metal electrode; 4 is a dielectric sleeve with a capillary hole (nozzle); 5 is an insulator; 6 is an opening for supplying working gas; 7 is a gas distribution system; 8 is a high-voltage power source; 9 is an irradiated biological object; 10 is an auxiliary electrode; 13 is a mesh electrode.

[0076] Fig. 16 shows a fragment of the emission spectrum of excited OH molecules (λ≈309 nm) in the interaction zone of the plasma jet and the irradiated object in the absence of a mesh electrode (curve 1) and the presence of a mesh electrode with zero (curve 2) and floating (curve 3) potential.

[0077] Figure 17 shows the proportion of surviving breast adenocarcinoma cancer cells (MCF-7) 24 hours after treatment with a cold plasma jet. The plasma jet was initiated by a sinusoidal voltage with a frequency of 13; 26 and 52 kHz, which corresponded to a current frequency of 13 kHz in the interaction zone with the cells placed in the wells of the plate with culture fluid. Untreated cells were used as a control. The plate with cells in the culture The 0078 liquid was placed on a grounded auxiliary electrode under the biological object (10 in the figures) at a distance of 33 mm from the nozzle, corresponding to a distance of 25 mm to the culture fluid. Cells were treated for 1 and 2 minutes at a voltage of 3.5 kV and a working gas (helium) flow rate of 9 l / min. With equal current frequencies in the plasma jet's impact zone on cancer cells, the mode with the higher frequency of the initiating sinusoidal voltage provides the greatest suppression of viability.

[0079] Figure 18 shows the proportion of surviving human lung adenocarcinoma cells (A549) 24 hours after treatment with a cold plasma jet initiated by unipolar positive pulses of 7 and 10 μs duration with a repetition rate of 30 kHz and a voltage amplitude of 4.2 kV for 1 and 2 minutes. Untreated cells served as a control. The plate containing the cells, suspended in culture fluid, was placed on a grounded auxiliary electrode under the biological object (designated 10 in the figures) at a distance of 33 mm from the nozzle, corresponding to a distance of 25 mm from the culture fluid containing the cells. The maximum cytotoxic effect was achieved by initiating the plasma jet with a voltage and a shorter pulse duration, all other conditions being equal.

[0080] Fig. 19 shows the efficiency of plasma jet irradiation under conditions of high humidity of 55% in the area of ​​action on malignant tumors in mice. Comparative data are given on the dynamics of malignant tumor development in mice (suspension of human glioblastoma cells (U87), 6 million cells / mouse, transplanted subcutaneously into Scid mice) after the first and subsequent (on days 2-5 and 7) days after irradiation (red line), as well as tumors in mice that were not irradiated (blue line). Plasma action was performed by initiating the jet with a sinusoidal voltage with a frequency of 52 kHz, a current frequency in the area of ​​action on the tumor of 13 kHz, a voltage of 3 kV, and a gas flow rate of 9 l / min. The distance from the nozzle to the mouse placed on a grounded additional electrode was 20 mm, the treatment time was 2 minutes. The days of irradiation are indicated by arrows in Fig. 19. Plasma treatment of tumors can slow tumor growth by 40%.

[0081] The following designations are used in the drawings and text:

[0082] U - voltage applied to the electrodes;

[0083] I - current recorded in the area of ​​impact of a low-temperature plasma jet on a biological object;

[0084] t - time;

[0085] λ - radiation wavelength;

[0086] Examples of the invention.

[0087] 1. Controlling the frequency of the current touching the irradiated object in the area of ​​​​exposure to the cold plasma jet and the object.

[0088] The method involves igniting a gas discharge in a channel by pumping a working gas using an initiating voltage applied to an internal discharge potential metal electrode (2) and an external discharge metal electrode (3) and using an additional metal electrode (11) under a floating potential, encircling the gas discharge channel on the outside in the gap between the internal potential and external grounded electrodes, providing regular conditions for reducing the current frequency, different from the voltage frequency, accompanied by an increase in the current amplitude and the pulse power introduced into the gas discharge (Fig. 3).

[0089] A sinusoidal voltage with a frequency of 10 to 60 kHz and an amplitude of up to 6 kV is used as the initiating voltage. When the working gas (helium) is supplied at a rate of 1 to 15 l / min and the appropriate voltage is applied to the internal discharge potential metal electrode (2) relative to the external discharge metal electrode (3), a plasma jet is generated, extending beyond the dielectric channel and propagating in free space. The area of ​​​​the plasma jet is determined by the cross-section of the jet and ranges from 1 to 4 mm 2. For a given frequency of the sinusoidal voltage applied to the internal discharge potential electrode (2 - in the figures) of more than 35 kHz, the frequency of the current in the interaction zone of the low-temperature plasma jet with an object located at a distance of 15 mm, at a voltage of 2.8 to 3.5 kV is 4 times less than the voltage frequency. For example, at a frequency of the applied sinusoidal voltage of 52 kHz, the frequency of the current contact in the area of ​​action on a biological object is 13 kHz (Fig. 4). At a voltage of more than 3.5 kV, the frequency of the current in the interaction zone of the low-temperature plasma jet with the object is less than the voltage frequency by 2 times. At a frequency of the applied sinusoidal voltage from 23 to 33 kHz, the frequency of the current in the interaction zone of the low-temperature plasma jet with the object at any voltage is 2 times less than the voltage frequency. For example, at a frequency of applied sinusoidal voltage of 26 kHz, the frequency of current in the area of ​​impact on a biological object is 13 kHz (Fig.5). When the frequency of the applied sinusoidal voltage is less than 20 kHz, the frequency of the current in the interaction zone of the low-temperature plasma jet with the object at a voltage greater than 3.5 kV is equal to the frequency of the applied sinusoidal voltage. For example, when the frequency of the applied sinusoidal voltage is 13 kHz, the frequency of the current in the area of ​​action on the biological object is 13 kHz (Fig. 6). With an increase in the frequency of the applied sinusoidal voltage in modes with equal current frequencies in the area of ​​interaction with the object, which can be multiples of the voltage frequency, the current amplitude increases (Fig. 7). An increase in the current amplitude leads to an increase in the pulsed power introduced into the gas discharge, which in turn leads to an acceleration of ionization processes, in particular, the intensification of the generation of the hydroxyl radical OH from H2O molecules with the subsequent occurrence of the reaction of the synthesis of H2O2 peroxide.

[0090] Reducing the frequency of the current reaching the object increases the amplitude, and thus increases the generation of reactive oxygen species, particularly OH. The presence of an additional electrode (11 in the figures) results in a stable division of the plasma jet current's frequency and, consequently, the ability to control the generation of hydroxyl radicals (OH).

[0091] 2. Controlling the duration of voltage pulses initiating a low-temperature plasma jet.

[0092] The initiating voltage is a pulsed voltage with an adjustable pulse repetition rate from 1 to 30 kHz, a pulse duration from 6 to 20 μs, and a voltage amplitude of up to 6 kV. When the working gas (helium) is supplied at a rate of 2 to 15 l / min and unipolar positive pulses with a voltage amplitude above 1.5 kV are applied to the internal discharge potential electrode (2) relative to the external discharge metal electrode (3), a discharge is ignited in the discharge gap. At a voltage above 1.5 kV, a low-temperature plasma jet is formed, propagating along the gas flow and extending beyond the dielectric channel into free space. The area of ​​action of the low-temperature plasma jet is determined by the cross-section of the jet and ranges from 1 to 4 mm2.At a given repetition rate of unipolar positive pulses greater than 17 kHz with a pulse duration greater than 10 μs, the current frequency in the interaction zone of the low-temperature plasma jet with an object located at a distance of 15 mm, at a voltage of 2.5-4.5 kV, is less than the voltage frequency by a factor of 2. At a given repetition rate of unipolar positive pulses greater than 17 kHz with a pulse duration less than 10 μs, the current frequency in the interaction zone of the low-temperature plasma jet with an object over the entire voltage range is equal to the frequency of the applied voltage (Fig. 8). Moreover, at the amplitude of the initiating voltage.

[0093] For voltages greater than 4 kV and all other conditions being equal, higher current amplitudes are achieved for pulses of shorter duration, while for initiating voltage amplitudes less than 4 kV, higher current amplitudes are achievable with longer durations. As the voltage pulse duration decreases, the current pulse amplitude increases, and the streamers that form the plasma jet become more intense and spread more regularly. Accordingly, the generation of the hydroxyl radical OH with radiation at a wavelength of λ≈309 nm intensifies. In the zone of interaction between the cold plasma jet and the object, the generation of active radicals increases (Fig. 9).

[0094] 3. Control of ambient humidity in the area of ​​impact of low-temperature plasma jet on a biological object.

[0095] A sinusoidal voltage with a frequency of 10 to 55 kHz or a pulsed voltage with an adjustable pulse repetition rate from 1 to 30 kHz, a pulse duration of 6 to 20 μs and a voltage amplitude of up to 6 kV is used as the initiating voltage. When the working gas (helium) is supplied at a rate of 2 to 15 l / min and the appropriate voltage is applied to the internal discharge potential electrode (2) relative to the external discharge electrode (3), a plasma jet is generated that extends beyond the dielectric channel and propagates in free space. The area of ​​​​the low-temperature plasma jet is determined by the cross-section of the jet and reaches from 1 to 4 mm 2 .

[0096] The technical result is achieved by placing the gas discharge device in a chamber made, for example, of polymethyl methacrylate or another gas-tight material, with internal dimensions of, say, 190 x 190 x 170 mm. The relative humidity in the chamber is regulated by a water vapor generator within a range of 20 to 90%. The gas discharge cell nozzle and the water vapor generator tube are inserted through openings in the top cover or side wall of the chamber.

[0097] A plasma jet impacts a biological object placed in a culture or physiological fluid on an auxiliary electrode, initiating chemical and biological reactions in the cells. Water evaporates from the liquid's surface, and the air humidity increases as it approaches its surface. Increasing humidity alters the plasma's properties and increases the rate of hydroxyl radical (OH) generation. Additional introduction of water vapor into the chamber intensifies the generation of hydroxyl radicals (OH) with radiation at a wavelength of λ≈309 nm in the interaction zone of the low-temperature plasma jet with the object (Figs. 10-12).

[0098] 4. Introduction of a specially shaped control electrode with zero and floating potential into the gap between the plasma jet generator nozzle and the irradiated object.

[0099] Pulsed voltage with a pulse repetition rate of 1 to 30 kHz, a pulse duration of 6-7 μs and a voltage amplitude of up to 6 kV is used as the initiating voltage. When the working gas (helium) is supplied at a rate of 2 to 15 l / min and unipolar positive pulses with a voltage amplitude above 1.5 kV are applied to the internal discharge potential electrode (2) relative to the external discharge electrode (3), a discharge is ignited in the discharge gap. At a voltage of more than 1.5 kV, a cold plasma jet is formed, propagating along the gas flow and extending beyond the dielectric channel into free space. The area of ​​​​impact of the low-temperature plasma jet is determined by the cross-section of the jet and reaches from 1 to 4 mm 2For a given repetition rate of unipolar positive pulses and pulse duration, the current frequency in the zone of interaction between the plasma jet and an object located at a distance of 15-30 mm, at a voltage of 2.5-4.5 kV, corresponds to the frequency of the initiating voltage pulses. A change in the electric field configuration in the plasma jet propagation zone in the nozzle-object gap when installing a control metal electrode (12) leads to a change in the energy distribution of electrons generated in the plasma jet propagating in free space, and accordingly, a change in the composition and concentration of active particles generated as a result of plasma-chemical reactions above the surface and in the cells of the biological object.

[0100] The technical result is achieved by the device of a control electrode (12), located perpendicular to the direction of propagation of the plasma jet at some distance from the nozzle of the jet generator, having an opening of arbitrary shape with a size greater than the transverse size of the plasma jet in this place and having a zero or floating potential, Fig. 13.

[0101] To change the energy distribution of electrons generated in the plasma jet, it is possible to simultaneously use the auxiliary (10) and control electrodes (12).

[0102] Study of the influence of the control electrode hole diameter revealed that 12 mm is the optimal size. This size maximizes the influence of the control electrode potential on the plasma jet's electrophysical parameters. Conversely, with a smaller size, such as 8 mm, parasitic discharge development occurs between the plasma jet and the control electrode. At larger sizes, the influence of the control electrode potential rapidly decreases with increasing hole size. Experimental and numerical simulation results demonstrated that the presence of a control electrode allows for increased generation of reactive oxygen species without altering the streamer propagation mode.Calculation of the ionization rate and experimental measurement of the emission intensity of helium atoms show that without a control electrode, the excitation and ionization rate in the streamer head increases monotonically as it approaches the cathode layer at the target surface, and then decreases. Placing a control electrode with zero potential in the jet propagation zone shifts the location of maximum energy deposition to the control electrode zone. Calculation of the potential distribution for the cases "without" and "with" a control electrode at zero potential shows that the presence of such a control electrode lowers the absolute value of the potential in the near-electrode zone. This leads to an increase in the potential gradient (electric field strength) in the streamer head, which, in turn, increases the ionization rate.

[0103] Fig. 14 shows the intensity distribution of OH molecules (λ≈309 nm) as a function of the nozzle-to-object distance for the cases "with" and "without" a zero-potential control electrode. The OH intensity distributions shown in Fig. 14 are experimentally measured values ​​in relative units (measured here and now).

[0104] The spectral fragments in Figs. 10, 11, 12, etc. have several peaks. The radiation at λ≈315 nm is the radiation of the second positive system of molecular nitrogen N2. The radiation at λ≈309 nm is the main band of the OH system.

[0105] In another implementation of the cold plasma jet generation installation, the technical result is achieved by installing a control mesh electrode between the nozzle and the irradiated object, which is a metal mesh cylinder having a diameter larger than the transverse dimension of the plasma jet and having a zero or floating potential (Fig. 15).

[0106] The results of the experiment and numerical simulation showed that, with the presence of a control grid electrode, it is possible to increase the generation of reactive oxygen species without changing the streamer propagation mode. It was found that placing a grid electrode with zero potential in the plasma jet propagation zone results in, for example, at a pulse repetition rate of 30 kHz, a pulse duration of 7 μs, and an electrode voltage of 4.2 kV, the intensity of the spectral line corresponding to OH hydroxide radiation (λ≈309 nm) increases approximately twofold with an increase in the water vapor concentration (humidity) in the affected area from 30% to 90%.

[0107] It has been established that the placement of a control grid electrode with a floating potential, for example, at a pulse repetition frequency of 30 kHz, a pulse duration of 7 μs and a voltage on the electrodes of 4.2 kV, the intensity of the glow of the spectral line corresponding to OH hydroxide (λ≈309 nm) increases by ~ 2.5 times, Fig. 16.

[0108] Thus, the technical result of the invention is:

[0109] controlling the intensity of active radical generation in the zone of interaction of the plasma jet with a biological object;

[0110] increase in the concentration of hydroxyl radicals OH;

[0111] increasing the reproducibility of biological effect;

[0112] reducing the thermal load on the object.

[0113] The technical result is achieved by the fact that in the method of controlling the generation of active radicals by a cold plasma jet of atmospheric pressure:

[0114] form a plasma jet in a gas discharge device with coaxial electrode geometry when pumping plasma-forming gas;

[0115] control the frequency of the current touching the biological object by changing the frequency and shape of the applied voltage; the configuration of the electric field in the zone of propagation of the plasma jet;

[0116] regulates the duration of voltage pulses that initiate the streamer discharge;

[0117] change the humidity of the environment in the area of ​​influence of the plasma jet;

[0118] Introduce control or grid electrodes into the gap between the nozzle and the object, which are under zero or floating potential, changing the distribution of the electric field and the energy spectrum of electrons.

[0119] The combination of these measures leads to an increase in the amplitude of current pulses and the pulse power of the discharge, which intensifies the plasma-chemical reactions of OH radical generation.

Claims

1. A method for controlling the generation of active radicals by a cold plasma jet at atmospheric pressure for biomedical applications, comprising forming a plasma jet in a gas-discharge device with coaxial electrode geometry during pumping of a plasma-forming gas, supplying the plasma-forming gas to a gas-discharge cell, igniting a gas discharge in it by supplying an initiating voltage to the discharge electrodes, forming a cold plasma jet extending beyond the gas-discharge cell, and exposing a biological object to said plasma jet, characterized in that the control of the intensity of generation of active radicals, primarily hydroxyl radicals OH, carried out by: a) regulation of the repetition frequency of current pulses reaching a biological object in relation to the frequency of the applied voltage by changing the parameters and shape of the initiating voltage; b) introducing a control electrode into the gap between the nozzle of the gas discharge device and the biological object, which is under zero or floating potential and changes the distribution of the electric field in the zone of propagation of the plasma jet; c) control of the ambient humidity in the plasma jet impact zone in the relative humidity range of 20-90%.

2. The method according to paragraph 1, characterized in that during sinusoidal initiation of the plasma jet, the initiating voltage is formed in the form of a sinusoidal voltage with a frequency of 10-60 kHz, and the frequency of the current pulses in the zone of interaction of the plasma jet with the biological object is set to be 2 or 4 times less than the frequency of the applied voltage by selecting the frequency range and voltage amplitude within 2.8-6 kV, an additional electrode is used, covering the gas discharge cell, located on the outer side of the dielectric housing, which is under a floating potential and ensures a change in the frequency of the current in the zone of action of the plasma jet on the biological object.

3. The method according to paragraph 1, characterized in that during pulsed initiation of the plasma jet by unipolar positive pulses: - the initiating voltage is generated in the form of pulses with a repetition frequency of 1-30 kHz, a duration of 6-20 μs and an amplitude of up to 6 kV; - the pulse duration is adjusted to control the amplitude of the current pulses and the pulse power of the streamers, while a decrease in the pulse duration leads to an increase in the specified parameters and an intensification of the generation of hydroxyl radicals OH.

4. The method according to paragraph 1, characterized in that the plasma-forming gas is helium supplied at a rate of 2-15 l / min, while the optimal intensity of the generation of hydroxyl radicals OH is achieved at a flow rate of 7-9 l / min and a relative humidity of the environment of 50-60%, which leads to an increase in the intensity of the spectral line of hydroxyl radical emission (λ≈309 nm) by at least 2 times compared to a humidity of 30%.

5. The method according to paragraph 1, characterized in that the control electrode is made in the form of a flat metal plate with a diameter of at least 16 mm with a round hole with a diameter of 12 mm, located perpendicular to the axis of propagation of the plasma jet at a distance equal to half the distance between the nozzle and the biological object, located under zero or floating potential.

6. The method according to paragraph 1, characterized in that the control electrode is made in the form of a metal mesh cylinder with a cell size of no more than 2 mm, with an internal diameter exceeding the transverse size of the plasma jet by at least 2 mm, with a height of 8-15 mm, located between the generator nozzle and the biological object, located under zero or floating potential, providing an increase in the intensity of the OH line radiation (λ≈309 nm) by at least 2-2.5 times.

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