SI21224A - Sterilization method using plasma and secondary source - Google Patents

Abstract

The subject of this invention is a method of plasma sterilization using radicals and a secondary source of radiation to this effect. To produce radicals within plasma, the discharge of various gases or their mixtures by some other, typically inert gases is used. A variety of discharge methods performed in a low-pressure area is used for this purpose. A secondary source of radiation, on the other hand, is provided by UV lamps or by gas discharge in a secondary chamber. The proposed method allows a very efficient and quick sterilization of various specimens, performed faster than by any of the traditional methods. It can also ensure low-temperature sterilization appropriate to highly sensitive medical instruments.

Description

1. DISPLAY OF THE PROBLEM

Although the study of inactive microorganisms began in 1950, the commercial sterilization of medical devices did not begin until 1990. (Seymour S., Disinfection, Sterilization, and Preservation, Chapter 38, p. 747.) It has traditionally been used in hospitals. enforced steam sterilization at 130 ° C or. dry heat for medical devices that withstand thermal stress; or ethylene oxide gas or low temperature formaldehyde vapor for heat sensitive devices. The increase in the use of moisture and heat sensitive medical devices, especially diagnostic or prosthetic devices, has also increased the need for sterilization as quickly as possible. However, the aforementioned methods are not relevant, since sterilization with ethylene oxide gas is quite time-consuming, because it is necessary to remove toxic ethylene oxide from the sterilized object, and consequently the process is also harmful to the atmosphere because it destroys ozone. Formaldehyde vapor has similar toxic effects to ethylene oxide.

The most common methods in the industry are steam sterilization methods, ethylene oxide, ionization and radiation sterilization with gamma radiation (cobalt 60) or electron beam. Although effective, these technologies are not suitable for widespread use of heat or moisture sensitive devices or even sterilization of plastic implants. The use of ionization and radiation sources has, in addition to the aforementioned disadvantages of the methods, a rather high cost. As a result, there is a need for a low-cost, efficient, fast, non-toxic and environmentally friendly sterilization method that can be carried out at low temperatures. The answer is low-temperature plasma sterilization.

Plasma as an unbalanced gas state can be divided into two categories. The first is high temperature plasma in excess of 5,000K. The second category, however, includes non-equilibrium or low-temperature plasma. These plasmas have electron energies in the range of 1 to 10 eV and electron densities of 10 ⁹ to 10 ¹² cm ³ . It is in these plasmas as well

U. Cvelbar, M. Mozetich

-2 lack of equilibrium between electron temperature T _e and gas temperature T _g . The ratio between them (T _e / T _g ) is typically 10 to 100. Due to this property, the nonequilibrium plasmas have sufficient energy to break the molecular bonds, and at the same time, due to the poor exchange of kinetic energy in the plasma, they act mildly on the surface of the workpiece. There are, however, different ways to generate these plasmas that have different properties depending on the generation. They differ mainly in the types of radicals, the amount of them, the temperature of the gas and electrons, and by-products such as light radiation.

Therefore, for plasma sterilization it is necessary to treat the surface with an unbalanced gas. The key to proper technological processing, however, is the mode of generation and parameters of the nonequilibrium states and the gas used to create the plasma. The most common method for generating highly unbalanced gas is to guide gas molecules through low-pressure discharge. In doing so, molecules are excited, dissociated, and ionized by inelastic collisions with electrons. Excited, atomized and ionized molecules are called radicals whose concentration depends on the discharge parameters. The concentration of radicals, however, is essential for the sterilization of the workpiece. Research has shown that two or three phases, which are cyclically alternating or complementary in each other, are important for sterilization. In the first one, we work on bacteria with UV light and cleave the bonds, and in the second we are helped by unbalanced plasma with reactive ions. In the third phase, the broken bonds are etched with the radicals of atoms by removing the individual broken bonds. The resulting products are pumped from the vacuum system.

2. BACKGROUND OF THE INVENTION

Perspectives on the use of plasma sterilization over the past few years have dictated quite a few, mostly academic, studies of spore sterilization in pure plasma gases such as H2, O2, Ar, N2, CO, NO, H2O2, etc., or in various H ₂ + gas mixtures Ar, O ₂ + Ar, N2 + Ar, NO + Ar, H2 + He, etc., and water vapor.

The gases that at the same time provided reactants and a high concentration of excited states that emit UV light proved to be the best. The rate of sterilization in a single plasma system depended primarily on the initial level of UV radiation, which cleaved the bonds of genetic material in spores. The reactants, however, broke the spores, heated them locally or partially etched.

Patented plasma sterilization procedures mainly refer to sterilization with different types of gas in a single plasma reactor. These are mostly microwave plasma reactors with lower concentrations of dissociated atoms. However, the processes are also patented in unitary DC reactors (RU2102084). Sterilization processes also apply to useful cases where we typically create plasma suitable for sterilizing individual products such as cans or bottles (US6230472, US5593649), decontamination of hazardous chemical gases with He / CE mixture (W00074730), or thin film sterilization.

U. Cvelbar, M. Mozetich

-3 Electron-jet Conveyor Belt (WO0115199). Atmospheric pressure sterilization from corona plasma for the packaging of food products is also very popular (WO03011346).

Gases used in a single vacuum chamber (US5650693) at a pressure of 0.1 to 10 mbar are gas mixtures consisting of (a) Ar, He, N ₂ , H2 or mixtures thereof and O2 and H2; (b) Ar, He, N2 or mixtures thereof with H2; (c) or mixtures thereof with O2 (EP0387022, US5115166, US5376332, US54137759, WO9526121). Sterilization plasmas were also generated with different gases: Ar, He or Xe (US3851436); Ar, N ₂ , O ₂ , He or Xe (US3948601); glutaraldehyde (US4207286); O ₂ (US4321232); Ar, N ₂ , O ₂ , He or freon at pulse pressure (US4348357). H ₂ O ₂ - hydrogen peroxide (US4643876) or mixtures ((a), (b), (c)) of the H ₂ O ₂ gases (EP0456135) mentioned above can also be used for sterilization. Plasma-pulse-vacuum cycles in these plasmas have also been patented (US5084239, US5178829). However, more exotic mixtures are also found such as H ₂ , O ₂ , N ₂ and H ₂ O (DE 10036550) or NO alone or O ₃ (JP162276-1983).

However, there is no literature on mixed sources for sterilization, where the plasma provides ions and atoms for the cleavage and etching of microorganisms from a secondary source, such as UV light or gamma radiation, which helps in the initial phase and further accelerates the cleavage of bonds in microorganisms. Such a method accelerates sterilization much more and works more efficiently.

3. DESCRIPTION OF THE PROBLEM SOLUTION

The invention encompasses a new plasma sterilization technology based on non-equilibrium plasma sterilization with a high dose of radicals and a secondary source of UV light.

In order to sterilize medical devices or any other items that we need sterile, we expose them directly to low pressure plasma. Plasma can be generated in various ways, primarily by discharge. Various direct and high frequency gas discharges can be used, such as smoldering, magnetron discharge, hot cathode discharge, hollow cathode discharge, radiofrequency discharge, microwave discharge, ECR discharge, laser discharge. Very suitable for low pressure plasma sterilization treatment is radio frequency or microwave discharge.

The charge in the reaction chamber is generated in pure oxygen or a mixture of oxygen and other gases. Primarily oxygen and inert gas mixtures such as argon or other noble gases or water vapor are used. Other gases may also be used; N ₂ , NO, N ₂ O ₂ , NH 3, H ₂ , H ₂ O ₂ , H ₂ O, CO, CO 2 _t CH 4, O ₃ , SO ₂ , EO, air, etc. or mixtures of these gases with one another or mixtures with the inert gases Ar, Ne, Xe, He, Rn.

U. Cvelbar, M. Mozetich

-4 From a secondary source, however, we provide radiation that allows for the initial and subsequent federal vaccination of the ligaments. damage to the genetic material of the micro-organisms. The use of UV radiation is the most appropriate secondary source, and gamma radiation can be used. UV radiation is generated or provided by separate excimer UV lamps (Fig. 1) or a secondary reactor in which plasma Hg, N2O2, N2, air or any other strong light source in the UV range is used as the radiation source (Fig. 2).

The use of UV radiation from a secondary source allows the direct destruction of the genetic material of the micro-organisms. The erosion of microorganisms by plasma in the primary reactor, however, is facilitated by dissociated plasma, which, by etching, creates volatile components of the products by etching. These products are usually the result of the interaction of radicals, most often plasma atoms. If oxygen atoms are used for the reactant, the results of such erosion are very effective as they aggressively interact with the microorganisms and effectively remove them from the surface, and the resulting products are usually ecologically harmless (H2O, CO2, etc.). At high concentrations of oxygen atoms, microorganisms on the surface can be oxidized very quickly if they do not have temperature-conducting contact with the substrate. In a similar way, they can also be removed from polymeric materials, where the use of such sterilization is well suited for artificial medical implants such as e.g. veins. Namely, the plasma exposure lowers the surface energy and inserts oxygen-rich polar groups on the surface such as (-OOH, OH, = 0, -CHO, -COOH) and leaves some bonds on the surface. This makes the adhesion of organic material such as human tissue much better and firmer.

Sterilization in the primary reactor is aided or abolished. such plasma containing ions that strike the surface of microorganisms and help to damage the genetic material is also desirable.

The method is optimized by using as many radicals as possible to aggressively participate in the erosion of microorganisms and ions that assist in erosion by damaging genetic material and grafting bonds on the surface. The secondary source ensures constant destruction of the genetic material and the cleavage of the ligaments, thus accelerating the sterilization process.

This procedure differs from other known methods, mainly in the two-component understanding of sterilization. All the procedures to date are based on plasma sterilization in a single system where the plasma from the gas mixture provides the source of UV light and at the same time radicals such as atoms. It is usually necessary to renounce some of the benefits of one or the other, and the resulting etching products may also be toxic and ecologically inappropriate. An example of using gas to provide both is NO or N2O2, but there is a high possibility of cyanide components being formed when etching microorganisms.

In our two-component process, a very good sterilization is possible in the low-pressure chamber due to the rapid and efficient treatment, which is also suitable for very sensitive materials or substances. Depending on the needs of the sterilization material, the parameters of sterilization can be adjusted by

U. Cvelbar, M. Mozetich

-5Different use of gases and regulation of continuous or pulsed operation of the plasma generator and secondary origin.

4. IMPLEMENTING EXAMPLES

The following is a description of two embodiments of secondary source plasma sterilization that explains the mechanism of this plasma sterilization technology. The sterilization method of the present invention is described by means of figures showing:

51.1 Schematic diagram of a plasma reactor for sterilization with a secondary UV light source with 3 separate UV lights.

51.2 Schematic of the layout of 3 separate UV lamps for the system of FIG. 1.

51.3 Schematic diagram of a plasma reactor for sterilization with a secondary UV light source from a secondary plasma chamber.

Figure 1 shows a schematic diagram of a plasma reactor with 3 UV sources, which are important in the first stage of sterilization, and subsequently allow for faster sterilization by cleavage of bonds in microorganisms. The plasma reactor consists of a discharge chamber (5), which in our case is a glass tube of 30 cm length and outer diameter. Gas is released into the chamber through the metering valves (3), which ensures the erosivity of the microorganisms with the plasma radicals. In our case, oxygen from the cylinder (1) or a mixture of oxygen and inert gas or hydrogen (a mixture of hydrogen with an inert gas) (2) is allowed to enter the chamber to ensure reactivity and homogeneity of the plasma in the reactor (5). We can also do this for various other gas mixtures from several other cylinders. Plasma reactor (5) generates plasma using an RF generator (6) having a rated power of 800 W and an industrial frequency of 27.12 MHz. The UV light source is provided by 3 excimer UV lamps (4) distributed symmetrically around the chamber. The chamber is continuously pumped with a two-stage rotary vacuum pump (10) at a nominal pumping speed of 64m ³ h '' via a molecular trap (9). Measure the pressure with a calibrated Prani vacuum gauge (8). The plasma is controlled by an optical catalytic probe (7).

Figure 2 is an example of the distribution of three UV lamps (4) around a glass cylindrical chamber (5) in which plasma is generated by an RF generator (6). Such a distribution ensures a relatively uniform distribution of the incident UV light on the sample to be sterilized.

Figure 3 shows a schematic of a secondary-chamber plasma reactor in which plasma is created, which is a strong source of UV light. The plasma reactor thus consists of two separate vacuum cylindrical discharge chambers. Into the reactor (5), where the samples are erosionally sterilized, gas is leaked through valves (3) from an oxygen cylinder (1) or a mixture of oxygen and inert gas or hydrogen (hydrogen mixture with inert gas) (2) to ensure reactivity and plasma homogeneity in the reactor (5). In the secondary reactor (13), which is separated from the rotary pump and the system via a valve (11), it injects gas from a cylinder (14) which

U. Cvelbar, M. Plasma gas discharge mech. N2O2 creates a source of UV light. This gas, in our case, is vented into the chamber after vacuuming via a rotary pump (10). The UV light source can also be provided by other gases such as N2 or even by venting through the valve (12). The discharge in the plasma primary and secondary reactor is generated by the same RF generator (6) having a rated power of 800 W and an industrial frequency of 27.12 MHz. The chamber is continuously pumped by a two-stage rotary vacuum pump (10) at a nominal pumping speed of 64m ³ h 'via a molecular trap (9). Measure the pressure with a calibrated Prani vacuum gauge (8). The plasma is controlled by an optical catalytic probe (7).

Claims (15)

PATENT APPLICATIONS 1. A method of sterilization treatment characterized by exposing the plasma sample and the secondary radiation source. 2. The method of claim 1, wherein the secondary radiation source is UV light or gamma radiation. Method according to claim 1, characterized in that the sample is exposed to oxygen radicals. Method according to claim 1, characterized in that the plasma is generated in a mixture of O ₂ oxygen and another gas, typically argon or other inert gas. 5. The method of claim 1, wherein the sample is exposed to water vapor (H2O, OH) or hydrogen peroxide (H2O2) radicals. Method according to claim 5, characterized in that the sample is exposed to a mixture of radicals with another gas, typically argon or other inert gas. Method according to claim 1, characterized in that the plasma is generated in a mixture of oxygen and nitrogen or in gases of nitrogen oxides such as nitrogen monoxide (NO), nitrogen dioxide (NO2), N2O2 and N20. Method according to claim 7, characterized in that the sample is exposed to a mixture of radicals with another gas, typically argon or other inert gas. U. Cvelbar, M. Mozetich 9. The method of claim 1, wherein the plasma is generated in a mixture of oxygen and carbon or in carbon monoxide gases such as carbon monoxide (CO) and carbon dioxide (CO ₂ ). 10. The method of claim 9, wherein the sample is exposed to a mixture of radicals with another gas, typically argon or other inert gas. 11. The method of claim 1, wherein the sample is exposed to sulfur dioxide (SO ₂ ), ethylene oxide (EO) radicals, or a mixture of these radicals with another gas, typically argon or other inert gas. Methods according to Claims 1-11, characterized in that the sample is subjected to continuous plasma action. Methods according to Claims 1-11, characterized in that the sample is exposed to the pulse action of the plasma. Methods according to claims 1-13, characterized in that the sample is exposed to the continuous action of the secondary radiation source. Methods according to Claims 1-13, characterized in that the sample is exposed to the pulse action of a secondary radiation source.