PLASMA DEVICE FOR TREATING LIVING TISSUES DESCRIPTION

Field of the invention

The present invention relates to a device for treating living tissues based on plasma technology. State of the art

The use of plasma is already known for treating living tissues. Specifically, one use is to achieve a loss in mutual adhesion between cells and in the attachment thereof to their substrate by effect of the interaction between plasma and cells. Another use consists in inducing programmed cell death (apoptosis).

Finally, a further use is to sterilise the treated area by killing bacteria therein without significantly damaging the cells forming the area.

Either one or the other effect is obtained by varying the current, the voltage and the frequency in the plasma devices as well as the duration of the treatment. Specifically, the plasma devices provided by the known art are based on the outflow of an inert gas that flows through a nozzle or hollow needle, so that an electric discharge of the "glow discharge" type or of the "electric arc" type is generated between said needle and the surface to be treated, as these are set at different potentials. The build-up of the electric discharge is allowed by the ionization of a fraction of the gas, that is by the generation of plasma. In turn, it is the current flow that maintains the process of plasma generation over time through the ionization of the neutral atoms by the electrons carrying such a current. Said devices are defined having a unipolar configuration, as said needle represents an electrode, whereas the surface to be treated forms the other electrode of the circuit that is therefore established, whereby the plasma is generated outside the device and the treatment takes place by direct contact, or nearly, of the plasma with the tissue to be treated. It is therefore apparent that the potential of the second electrode is not irrelevant. Specifically, the circuit consisting of the needle/tissue does not have a reference potential, with the subsequent risk of a possible generation of electric discharges concentrated between the needle and the tissue with the subsequent damaging of the tissue itself.

Another problem depends on the fact that, as the production of plasma is associated to a gas heating, when it is produced externally, the gas flow results potentially detrimental for the substrate to be treated. Summary of the invention It is the object of the present invention to overcome all of the aforesaid drawbacks and to provide a device for treating living tissues for the purpose of obtaining effects such as sterilization, cell detachment, cell apoptosis or tissue necrosis, as well as other possible non-destructive interactions.

The object of the present invention is a plasma device for treating living tissues, which, according to claim 1 , includes:

- a pair of electrodes one of which is connected to a reference potential;

- an electric generator connected to said electrodes, adapted to generate a potential difference varying over time therebetween;

- a duct, one end of which is connected to a gas source and the other end of which contains said electrodes, so that the gas is converted to plasma just before exiting the duct.

The gas employed to generate plasma may be helium, argon or another noble gas, or a mixture thereof, and it may contain higher or lower fractions of nitrogen, oxygen or other reactive gases. Said device may be applied in the sterilization of tissues, avoiding the damaging of the possible substrate, as the aforesaid device forms a bipolar system, including at least one pair of electrodes required for the generation of plasma. Specifically, the two electrodes are connected to an electric radiofrequency generator, and one of the two electrodes is connected to a reference potential that may be equivalent to ground.

Accordingly, the plasma is produced within the device itself, from which a flow exits substantially consisting of neutral atoms or molecules and active chemical species, thereby avoiding that the electrodes come into contact with the substrate to be treated. Advantageously, said device results safe due to the absence of electric discharges between the device and the tissue, which therefore does not represent the second electrode and, furthermore, a low temperature of the gas is ensured, it being ideal for the substrate not to be damaged during treatment.

Therefore, a specific object of the present invention is a plasma device for treating living tissues, as described in greater detail in the claims. The dependent claims disclose preferred embodiments of the invention. Brief description of the Drawings Further features and advantages of the invention will become more apparent in light of the detailed description of a preferred though not exclusive embodiment of a plasma device for treating living tissues, which is shown by way of non-limitative example with the aid of the accompanying drawings in which: Figure 1 shows the schematic diagram of a plasma device; Figure 2 shows the decreasing trend of the number of bacterial colonies as the treatment time increases with the present device, with a 90% reduction in a treatment of about 1 minute.

Detailed description of a preferred embodiment of the invention A preferred embodiment of the device, which is shown in Figure 1 , provides for a pair of electrodes 6 and 9 consisting of two concentric nozzles, one inserted into the other and reciprocally insulated by means of an tube 7 made of insulating material, which is placed between the two and is as long as the electrode 9. The inner nozzle 6 forms the duct through which the gas flows and ends internally to the outer nozzle 9, so that a special area 12 is formed for the generation of plasma. Therefore, the latter results between said tube 7 made of insulating material and the inlets of both electrodes.

The inlet of the nozzle forming the inner electrode 6 is overlapped by a grid 10 made of conductive material and the inlet of the nozzle forming the outer electrode 9 is overlapped by a grid 1 1 made of conductive material. Both grids are galvanically connected with respective electrodes. Said grids are adapted to improve the generation of plasma and with reference to the specific application, they are from a few tenths of millimetre to some tens of millimetre away from one another. Said electrodes and therefore said grids are subjected to a potential difference, as they are electrically connected to said electric generator 1 , which is specifically an electric radiofrequency generator, by means of a coupling circuit 2, designated as Matching Network, which serves to minimise the power reflected towards the electric generator and to increase the voltage to the required values to ionize the

gas.

Among the two electrodes, it is preferred that the electrode 9 and the grid 1 1 are galvanically connected to ground potential.

The free end of the inner electrode 6 is provided with a bayonet joint 5 of the known type, for an easy connection of the device to said gas source.

Both grids may be flat, concave or convex, although it is preferred for the grid 1 1 to be flat and for the grid 10 to be convex, the convexity being towards the grid 1 1. The electrodes 6 and 9, which are insulated by the insulating tube 7, are held in position by a support structure 8. Therefore, the gas flow 5 is introduced through said joint, which flows within the inner electrode 6 up to the end fitted with the grid 10. By flowing through the area 12, the gas is transformed into plasma by the effect of the electric field induced by the generator on the grids, which varies over time at a frequency between 1 and 30 MHz and displays a potential difference of the order of one kV. The generator provides a power of the order of ten W, from 1 to 30 W, with an optimal value of 10 W, a considerable fraction of which is dissipated within the coupling circuit. The plasma flowing out from the device hits the cell substrate to be treated. Some preferred gases are helium, argon mixed with air, oxygen, nitrogen and mixtures thereof and/or other gases, to form a flow in the range between 0.1 and 5 litres/minute. Specifically, the use of noble gases may be avoided, for example, by increasing the potential difference between the electrodes. Therefore, said device may be applied, among other uses, to treatments aimed at the sterilization of the substrate, for example, for the therapy or the prevention of infections, to treatments aimed at detaching cells from the substrate, and to treatments to induce cell apoptosis.

A preferred application method provides that the optimum distance between the outer grid 1 1 and the substrate to be treated varies between 0 and 2 cm, whereas the optimum application time is in the range between 10 seconds and 5 minutes. Advantageously, the low value of the power coupled with the plasma ensures that the latter is formed without the gas flow significantly heating. Thereby, the plasma results poorly ionized, i.e. most of the gas remains in the form of neutral atoms or molecules and in a non-equilibrium state, characterised by an electronic

population at high temperature, that is of the order of some electronvolts, thus of some tens of thousands of Kelvins, and a ion population at room temperature. A plasma displaying these features is usually defined as a "low temperature plasma". Such a condition allows to prevent the occurrence of any thermal damage on the substrate to be treated.

Furthermore, including at least one pair of electrodes subjected to a known potential difference - one electrode (preferably the outer one) being set at a ground potential - ensures the total absence of electric discharges between the device and the substrate, thus avoiding the subsequent damaging thereof. Experimental results with an application in the field of ophthalmology.

The device has been applied for times varying between 30 seconds and 5 minutes to bacterial suspensions in Luria placed in wells. Some untreated control samples have been kept in the same temperature conditions as those exposed to plasma. After the treatment, each sample has been plated on an appropriate agar substrate and incubated at 37°C for sixteen hours. The number of colonies grown on each culture plate has been considered representative of the number of bacteria that survived the treatment. The tests have been carried out on Escherichia CoIi. The graph represents the number of residual bacterial colonies as the exposure time varies (the value for t = 0 is that relative to the control samples). In Figure 2, a clear decrease may be noted in the number of colonies as the treatment time increases with a reduction of 90% in about 1 minute. A treatment has also been carried out on a pig's eye on which a bacterial corneal ulcer had previously been induced. In this test, a 70% reduction in the bacterial charge has been noted as compared to control samples, after a treatment of 2 minutes, whereas the histological test under an optical microscope has not highlighted alterations of the cell structure of the corneal surface. The specific modes to embody the invention described herein do not limit the content of this application, which includes all of the variants of the invention according to the claims.