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Gas Discharge Sterilization in Medicine

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Development of Technology for Medical Instrumentation Sterilization by means of Gas Discharge Technique

Tech Area / Field

  • PHY-PLS/Plasma Physics/Physics
  • BIO-SFS/Biosafety and BioSecurity/Biotechnology
  • MED-OTH/Other/Medicine

Status
3 Approved without Funding

Registration date
11.08.2000

Leading Institute
MIFI, Russia, Moscow

Supporting institutes

  • Research Center of Toxicology and Hygienic Regulation of Biopreparations, Russia, Moscow reg., Serpukhov\nVNIIEF, Russia, N. Novgorod reg., Sarov

Collaborators

  • Texas Technical University / Pulsed Power Laboratory / Department of Electrical Engineering and Physics, USA, TX, Lubbock

Project summary

The Project objectives are the development of an effective technique for the medical instrumentation sterilization by means of gas discharge technology; the construction of an experimental equipment prototype for sterilization of products made of solid materials (including heat-sensitive materials); the analysis of perspectives of gas discharge technique application for the sterilization of porous materials and medical waste.

At present the following techniques are used for the purposes of sterilization of medical instrumentation, laboratory equipment and media to be used for the operation with germ cultures: high temperature processing, treatment of products by means of chemically active gases and liquids and processing of products by flows of ionizing and ultraviolet (UV) radiation.

The high temperature techniques of sterilization include the processing of corresponding products with dry hot air and with the overheated saturated vapor under high pressure. In the first case sterilization is realized in dry heating boxes, whereas in the second one it is effected in autoclaves. Such techniques are widely used nowadays. At the same time they are characterized by the substantial inertia of heating and cooling processes as well as long duration of the sterilization process itself. They require rather appreciable energy consumption whereas the total automatization of the technological process is questionable due to a great number of mechanical and electromechanical by-pass and cut-off elements. In addition, the high temperature techniques couldn't be used for the sterilization of temperature sensitive materials because the environmental temperature could reach 150–200 °C. As for viruses, they could be disactivated not in all cases, especially in autoclaves. There is also the fire prevention problem in case of materials processing in dry heating boxes. The possibility of accidental outstream of overheated vapor from the autoclave should be taken into consideration as well.

The low temperature ("cold") sterilization technologies include the materials processing with gasiform (ethyleneoxide, ozone, vapors of formaldehyde solution etc.) and liquid (iodoform, hypochlorite, ethanol and phenol based compositions) chemically active substances. The efficiency and extent of desinfection by these substances are not the same and depend on their chemical activity. The number of microbiological cultures which can be sterilized by "cold" techniques are substantially less as compared with high temperature ones. In addition, they mainly cover the highly organized forms. The "cold" sterilization is less effective. Moreover, all desinfecting substances used in "cold" techniques are toxic. Most of them irritate eyes, skin and lead to corrosion of the equipment material.

Among the sterilization techniques the use of ionizing radiation (electron beams, X-rays) is of a specific character. Such a technique is realized by means of electron accelerators with 2–5 MeV energy range, the sterilization doses being equal 3–10 Mrad. The high efficiency of that technique should be noted. It provides secure desinfection of various materials including the thermosensitive ones. Nevertheless, accelerators are usually very expensive, they require specially equipped radiation safe rooms. In addition, highly qualified operational personnel is required.

As for the ultra-violet technique of sterilization, it is commonly used for air desinfection (quartz lamps).

For the last years active research intended to use the sterilizing effect of the gas discharge plasma, in particular, the glow discharge of atmospheric air is under way.

The technology suggested by the Project authors consists of the processing of objects to be desinfected by means of the low temperature plasma of pulse-periodical diffusion gas discharge [1-3]. It is shown that in some regimes of the high voltage pulse diffusion discharge at pressures up to atmospheric one electrons are generated with energies substantially higher than the energy of electrons in the glow discharge. With transition into medium and low gas densities the efficiency of high energy electrons generation increases. It is also shown that such regimes of the discharge could be formed in a large space even at atmospheric pressure [4-6], the latter being of great advantage.

The sterilizing action of the high voltage discharge plasma is effected by sterilization agents: charged particles, hard ultra-violet radiation, highly exited neutrals and active products of plasma-chemical reactions. The corresponding kinetic energy of charged particles, state energy of neutrals and ions (including metastable ones), energy of quants in plasma of some diffusion discharge types substantially exceed the energy required for the disactivation of viruses as well as germ cultures. The authors have developed and built effective transistor generators of misrosecond duration high voltage pulses which secured the formation of such a discharge at frequencies up to 50 kHz [7, 8]. The discharge was successfully used for the decomposition of such stable molecules as CCl4, trichloroethylene et al. [9, 10] as well as for the ozone synthesis [11, 12].

The results that are to be obtained during the Project implementation would make it possible to develop a new sterilization technology based on the processing of products by means of the high voltage diffuse discharge plasma. Such a technology would have the following merits as compared to other ones:

– the wide variety of sterilization agents (charged particles, hard UV-radiation, exited neutrals, active products of plasma-chemical reactions). The qualitative and quantitative composition of agents can be changed according to a given computer program during the desinfection cycle;

– low sterilization temperatures that makes it possible to disinfect thermosensitive materials;

– small duration of the sterilization process;

– large space of operational chambers, no excessive pressures in them, their fire-safety, the technology ecological purity, low energy consumption (about some watts), low cost of the equipment;

– possibility of total automatization of the sterilization process;

– the equipment operation doesn't require qualified personnel, the work can be done by medical personnel of medium and low qualification.

Works to be executed in the Project framework include:

– determination of optimal configuration of the system of electrodes, power supply parameters and discharge regimes which makes it possible to minimize the energy required for the sterilization;

– determination of inactivating factors and agents which secure sterilization in different discharge regimes;

– obtaining of experimental results on disactivation of Gram-negative and Gram-positive vegetative forms of microorganizms, spore forming bacilli and acid-proof microorganizms;

– development of an experimental prototype of the equipment to be used for sterilization of products made of solid materials (including dielectric thermosensitive ones);

– study of a possibility to use the gas discharge technology for the disinfection of products made of porous materials as well as medical waste.

Determination of optimal version of the electrode system is supposed to be performed by means of numerical simulation of electrical fields and potentials inside the operational chamber of the equipment. The choice of optimal regimes of discharge, the development of necessary electrical supply sources and determination of main factors of sterilization (besides numerical calculations and simulation) would require the experimental determination of parameters of the multicomponent thermononequilibrium discharge plasma and building dummies of the source. Plasma parameters are supposed to be determined by means of electrical, optical, spectroscopic and probe measurements. The problem of dielectric objects electrization could be solved by means of bipolar pulses application. It is intended to use cultures recommended by the World Health Organization for the biological testing of the treatment. An experimental prototype of the equipment as well as diagnostic benches are supposed to be assembled with use of the equipment available at the Project participating institutions.

Results obtained in the process of Project implementation would have the commercial potential. Scientists and experts who dealt with the development and production of mass destruction weapons are expected to take part in the solution of Project problems. So, Project objectives correlate with those of ISTC. Project participants have long standing experience in the fields of pulsed power and medical instrumentation sterilization.

Literature:

1. Pavlovsky A.I., Bosamykin V.S., Karelin V.I., Nikol'ky V.S. Electric Discharge OQG with Initiation in Active Space. Kvantovaya electronika. v.9 #3, 1976, pp.601-604 (in Russian).

2. Pavlovsky A.I., Buranov S.N., Gorokhov V.V., Karelin V.I., Repin P.B. et.al. Microstructure of Current Channels and Acceleration of Electrons in High Voltage Glow Discharge at Atmospheric Pressure. V All-Union conference on gas discharge physics (Abstracts). Omsk, 26-28 June 1990, book 1, pp.196-197, Omsk State University Publication, 1990 (in Russian).

3. Buranov S.N., Gorokhov V.V., Karelin V.I., et.al. Runaway Electrons in Microchannels in High Voltage Glow Discharge in Air at Atmospheric pressure. Proceedings of XX Intern.Conf. on Phenom.Ioniz.Gaz. Piza., Italy v.2, 1991, pp.466-467.

4. Karelin A.I. Formation of spacely uniform self-discharges in large volumes of dense gases. In Proceedings of 2 All-Union conference on Physics of electrical break down of gases (abstracts), Tartu, 5-8 of June 1984, part 2, pp.339-341. Tartu State University Publication, 1984 (in Russian).

5. Karelin A.I., Repin P.B. Formation of a self-discharge in the volume up to 10 l of dense SF6. In Proceedings of 3 All-Union Conference on gas discharge physics (abstracts). Kiyev, 21-23 of October 1986, part 2, pp.348-350, Kiyev State University Publication, 1986 (in Russian).

6. Pavlovsky A.I., Bosmanov V.F., Bosamykin V.S., Karelin V.I et.al. Electric Discharge CO2-laser with 0.28 m3 volume of active region. Kvantovaya electronika. v.14 #2, 1987, pp.428-430 (in Russian).

7. Buranov S.N., Gorokhov V.V., Karelin V.I., Repin P.B. Transistor generator of high voltage pulses with alternating polarity. Pribory i Technika Experimenta, 1999, #1, pp.134-136 (in Russian).

8. Buranov S.N., Gorokhov V.V., Karelin V.I., Repin P.B. Quasi-resonant transformer of direct voltage capacitive store. Pribory i Technika Experimenta, 1999, #2, pp.84-87 (in Russian).

9. Buranov S.N., Voyevodin S.V., Voyevodina I.A., Gorokhov V.V. et.al. Pulse-periodical glow discharge in mixtures of air with organic ingredients. In “Research on plasma physics”. Sarov-city, RFNC-VNIIEF, 1988, pp.339-361 (in Russian).

10. Buranov S.N., Voyevodin S.V., Voyevodina I.A., Gorokhov V.V. et.al. Destruction of organic impurites by means of high voltage glow discharge. All-Russian conference "New in Ekology" (reports and abstracts). St.Peterburg, 16-18 of June 1998, v.3, p.178 (in Russian).

11. Buranov S.N., Gorokhov V.V., Karelin V.I., Repin P.B. Pulse -periodical systems for ozone generation by means of microsecond duration discharge at the repetition rate up to 50 Hz. 2 All-Russian conference "Ozone in biology and medicine", Nizhny Novgorod, 6-8 of September 1995, p.102 (in Russian).

12. Karelin V.I., Buranov S.N., Gorokhov V.V., Repin P.B. Wide-range Medical Ozonator with Precise Low-Concentration Ozone Generation. 12 IEEE Intern. Pulsed Power Conference, June 27-30, 1999, Monterey, California, Digest of technical papers. pp 1421-1424.


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