CA1104322A - Seeded gas plasma sterilization method - Google Patents
Seeded gas plasma sterilization methodInfo
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- CA1104322A CA1104322A CA342,074A CA342074A CA1104322A CA 1104322 A CA1104322 A CA 1104322A CA 342074 A CA342074 A CA 342074A CA 1104322 A CA1104322 A CA 1104322A
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Abstract
Abstract of the Disclosure Sterilization of the surfaces of objects is achieved by placing the same in a continuous flow of a low temperature, low pressure gas plasma, containing small amounts of aromatic, heterocyclic, saturated or unsaturated aldehydes alone or mixtures thereof. The gas plasma is a partially ionized gas composed of ions, electrons and neutral species, which may be formed by electromagnetic discharges at subatmospheric pressure in the 1 to 300,000 Megahertz range, and corresponds to a minimum average spatial energy density of 0.001 watts per cubic centimeter. The gas plasma may also contain other vaporized cidal agents. Contrary to most gaseous steriliza-tion procedures, the method is safe, allows quick handling of heat sensitive items, does not corrode equipment and does not leave toxic residues.
Description
SL~EDED GAS PLASMA STERILI ZATION METHOD
This invention relates to gaseous sterilization by the treatment of objects or materials with a chemical in the gaseous or vapor state to destroy all microorganisms with which they have been contaminated. The need for such a method of sterilization has developed from the use of many items that cannot be subjected to heat, radiation, or liquid chemical sterilization.
In practice, only two gases or vapors have been commercially used on a large scale for surface sterilizing purposes and these are formaldehyde vapors and ethylene oxides gas. However, each suffer from drawbacks.
Formaldehyde vapors have been used as a fumigant for many decades in the h~spital, agricultural and industrial fields. The limitations of this technique are numerous.
To kill tough aerobic and anaerobic bacterial spores at room temperature, one needs at least a 24 hour contact time with a vapor having at least 70% relative humidity. This type of vapor is extremely corrosive and the fumes are very irritating.
It is also very difficult to maintain a hîgh level of formaldehyde gas since CH2O is stable in high concentrations only at temperatures above 80C in humid air. At ordinary room temperatures formaldehyde gas quickly polymerizes and it dissolves readily in the presence of water. Thus gaseous sterilization with formaldehyde can be regarded as a I misnomer because introduction of formaldehyde gas into a closed space serves mainly as a mechanism for distributing either moisture films in which formaldehyde is dissolved or
This invention relates to gaseous sterilization by the treatment of objects or materials with a chemical in the gaseous or vapor state to destroy all microorganisms with which they have been contaminated. The need for such a method of sterilization has developed from the use of many items that cannot be subjected to heat, radiation, or liquid chemical sterilization.
In practice, only two gases or vapors have been commercially used on a large scale for surface sterilizing purposes and these are formaldehyde vapors and ethylene oxides gas. However, each suffer from drawbacks.
Formaldehyde vapors have been used as a fumigant for many decades in the h~spital, agricultural and industrial fields. The limitations of this technique are numerous.
To kill tough aerobic and anaerobic bacterial spores at room temperature, one needs at least a 24 hour contact time with a vapor having at least 70% relative humidity. This type of vapor is extremely corrosive and the fumes are very irritating.
It is also very difficult to maintain a hîgh level of formaldehyde gas since CH2O is stable in high concentrations only at temperatures above 80C in humid air. At ordinary room temperatures formaldehyde gas quickly polymerizes and it dissolves readily in the presence of water. Thus gaseous sterilization with formaldehyde can be regarded as a I misnomer because introduction of formaldehyde gas into a closed space serves mainly as a mechanism for distributing either moisture films in which formaldehyde is dissolved or
2~104;~zz solid formaldehyde polymers over all available surfaces within the enclosed space. Very inConsistent and sometimes contradictory results have been reported in hospital disinfection, patient rooms, bedding, etc.,and in agricultural applications such as eggs and hatcheries sanitizing. Formaldehyde vapor has a very weak penetrating ability and, if used in an a.tmosphere with traces of hydrochloric acid, it can quickly produce at 70C
an~ 40% relative humidity) bis-(chloromethyl)-ether, which is a carcinogenic agent.
To minimize the abovementioned drawbacks in hospital applications, a new approach was recently developed which combines the use of subatmospheric steam and formaldehyde gas at 80C in autoclaves. This method i~s said to kill most sporulated microorganisms at the concentra-tion normally encountered in hospital practice while decreasing the aldehyde residue on instruments. It requires a time exposure of t-~o hours with a formalin concentration of 8 gr. per cubic foot of autoclave.
~lowever, despite the long contact time and the relatively high ~emperature, the method does not satisfy the stringent requirements of the sporicidal AOAC (Association of Official Analytical Chemists) test in the United States of America.
From the foregoing, it is apparent that formal-dehyde vapors, besides their toxicity and irritating charac-teristics, are difficul.t to handle at room temperatures and they do not provide a fast and reliable method to satis-factorily handle most of the hospital and industrial applica-30 tions.
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an~ 40% relative humidity) bis-(chloromethyl)-ether, which is a carcinogenic agent.
To minimize the abovementioned drawbacks in hospital applications, a new approach was recently developed which combines the use of subatmospheric steam and formaldehyde gas at 80C in autoclaves. This method i~s said to kill most sporulated microorganisms at the concentra-tion normally encountered in hospital practice while decreasing the aldehyde residue on instruments. It requires a time exposure of t-~o hours with a formalin concentration of 8 gr. per cubic foot of autoclave.
~lowever, despite the long contact time and the relatively high ~emperature, the method does not satisfy the stringent requirements of the sporicidal AOAC (Association of Official Analytical Chemists) test in the United States of America.
From the foregoing, it is apparent that formal-dehyde vapors, besides their toxicity and irritating charac-teristics, are difficul.t to handle at room temperatures and they do not provide a fast and reliable method to satis-factorily handle most of the hospital and industrial applica-30 tions.
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3 110a~3Z2 In the past two aecades ethylene oxide (ETO) has become the most popular method to gas sterilize both in hospitals and industry. While initially ETO seemed an ideal technique to replace formaldehyde fumigants, very serious limitations from the toxicity viewpoint have recently attracted the attention of health authorities.
The average time needed to sterilize medical instruments in an ETO unit is 180 minutes at 30C., but it has to be followed by a long de-aeration period. For instance, the de-aeration time for medical devices is between 2 and 8 hours in a de-aerator machine, but it oscillates between 1 and 8 days at room temperature. On rubber gloves, the residues can burn the hands; on tubes carrying blood, they will damage red blood cells and cause hemolysis. Endo-tracheal tubes which are not properly aerated can causetracheitis or tissue necrosis.
Besides the risks due to the toxicity of ETO
residues, other accidents have been reported due to the ex-plosive characteristics of pure ETO. As little as 3%
ethylene oxide vapor in air will support combustion and will have explosive violence if confined. To solve this problem, various diluent gases such as CO~ or fluorinated hydro-carbons have been mixed with ETO in some commercial formulations.
It is apparent, therefore, that ETO sterilization became widely used not because it was an ideal sterilant, but rather since there seemed to be no alternative gas steri-lant method which was capable of as fast a sporicidal action without any drawbacks from the toxicological or environmental : 30 viewpoint.
~0~3Z2 The present invention provides an alternative to ETO sterilization with the advantages of faster sporicidal action, no de-aeration period, no toxic residue, and no explosion risk. Moreover, this invention provides a more 5 economical approach from the running and investment cost view-point when comparing the volume of material treated per unit of time.
In accordance with the present invention, there is provided a method of sterilizing a surface comprising con-10 tacting the surface with a low temperature gas plasma contain-ing at least 10 mg/l of an aldehyde under a subatmospheric pressure.
The term "Sterilization" as used herein refers to sporicidal action against Bacillus subtilis ATCC (American 15 Type Culture Collection) 19659 and Clostridrium sporogenes (ATCC 3584) because they are the resistan~ microorganisms used in the fumigant-sterilant test according to the requirements of the AOAC (Official Method of Analysis of the Association of Official Analytical Chemists, 12th ed., Nov. 1975).
20 The destruction of these two resistant species of spores by the AOAC procedure leads automatically to the destruction of other less resistant microorganisms, such as, mycobacteria, non-lipid and small viruses, lipid and medium size viruses, and vegetative bacteria.
A better understanding of the cidal mechanism of a low temperature gas plasma in accordance with this invention may be had by consideration of the physical structure of a highly resistant spore. Figure 1 represents the typical structure of a typical bacterial spore. The typical bacteria 30 spore is surrounded by an exosporium which is a loose sac 110~3Z2 peculiar to so~e spores species, and possesses, from the outside to the inside, successively, (a) multi-layered coats containing disulphide (-S-S-) rich proteins, (b) a thick cortex layer which contains the polymer murein (or peptido-5 glycan), (c) a plasma membrane, and (d) a core or sporeprotoplast.
The first line of resistance of the spore to exo-genous agents consists of the proteinaceous outer coats which contain keratin-like proteins. The stability of keratin 10 structures is due to frequent primary valence cross links (disulphide bonds) and secondary valence cross links (hydrogen bonds) between neighboring polypeptide chains. Keratin like proteins are typically strong, insoluble in aqueous salt solutions or in diluted acid and basic solutions, and are 15 resistant to proteolytic enzymes and hydrolysis. The layered outer coats, thus, are rather inert and play a predominant role in protecting the spore against exogenous agents. They seem to play an important role in cidal action through physical or chemical modifications which affect the diffusion 20 of cidal molecules, excited atoms or radicals inside the microorganism protoplast.
To alter the multilayered outer coats and thus allow further penetration and possible interactions in the critical cortex or protoplast regions, a very active agent mus be 25 chosen, and it has been found that an ionized gas plasma is an excellent vehicle to provide reactiYe atoms, free radicals, and molecules which will drastically alter the protective layers of bacteria, fungi, and spores. The presence of small amounts of aldehyde vapors in the ionized low tempera-llOi3~2 ture non-oxidizing gas plasma, in accordance with this inven- I
tion, leads to the destruction of sporulated and non- ¦
sporulated microorganisms.
In the present invention, the objects to be decon-5 taminated are exposed to a continuous flow of low temperaturegas plasma seeded with a small amount of an aldehyde, usually an aromatic, heterocyclic, saturated or unsaturated aldehyde.
The gas plasma is a partially ionized gas composed of ions, electrons, and neutral species.
The low temperature gas plasma is formed by gaseous electric discharges. In an electrical discharge, free elec-trons gain energy from the imposed electric field and lose this energy through collisions with neutral gas molecules.
The energy transfer process leads to the ormation of a 15 variety of highly reactive products including metastable atoms, free radicals, and ions.
For an ionized gas produced in an electrical dis-charge to be properly termed a "plasma", it must satisfy the requirement that the concentrations of positive and negative 20 charge carriers are approximately equal. The plasma used in the present invention are glow discharges plasma and are also termed "low temperature" gas plasma. This type of plasma is characterized by average electron energies of 1 to 10 eV and electron densities of 109 to 10 2 per cm . Contrary to the 25 conditions found in arcs or plasma jets, the electron and gas temperatures are very different due to the lack of thermal equilibrium. In a glow discharge, the electron temperature can be ten to a hundred times higher than the gas temperature.
The latter property is important when sterilizing the surfaces 30 of thermally sensitive materials.
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7 :1104322 r In the low temperature gas plasma used in this invention, there can be distinguished two types of reactive elements, i.e. those which consist of atoms, ions or free radicals and those which are small high energy particles 5 such as electrons and photons. In glow discharges a large amount of ultraviolet radiation (UV) is always present.
The UV high energy photons (3.3 to 6.2 eV) will produce strong cidal effects because they correspond to a maximum of absorption by DNA (deoxyribonucleic acid) and other nucleic 10 acids~ However, in the case of spores which can reach one millimeter in diameter, photon energy can be quickly dissipa-ted through the various spore layers and this may restrict photochemical reactions to outer coats. The photon energy is rather restricted to thin layer surface modifications and is, 15 therefore, more efficacious when dealing with the smaller non-sporulated bacteria. In the case of high resistance spores, the photonic action may contribute to partial alteration of the disulphide rich proteins coat and thus facilitate the diffusion of free radicals, atoms, or excite~molecules inside 20 the core region.
In the present invention, small amounts of vaporized aldehyde monomers and free radicals present in a low tempera-ture gas plasma can greatly increase the overall biocidal action of a gas plasma.
The exact mechanism whereby enhanced sporicidal activity is attained using the aldehyde-seeded plasma stream is not fully understood, but some mechanis~ can be considered.
For example, due to the presence of atomic or excited oxygen in the gas phase, the aldehydes may produce short life very 30 reactive epoxides and other intermediates and free radicals ~10~322 which may interact with many proteins and nucleic acids groups in outer layer coats and thereby improve diffusion of cidal groups.
The next possible step in the diffusion of cidal 5 groups is the penetration inside the cortex layer whose major component is the polymer murein (or peptidoglycan).
Murein is a large, crosslinked, net-like molecule. A con-jugat~d attack by atomic oxygen and aldehyde radicals on the polymer rapidly shakes and modifies the tight polymer 10 structuxe of the cortex layer, leading to its destruction.
In addition, there is the potential for alteration of the hypothetical pathway of dipicolinic acid synthesis by the aldehydes. It has long been speculated that since calcium and dipicolinic acid (DPA) occur in spores in roughly equimolar lS amounts, they form a salt complex whose role is capital in spores resistance. The exact location of the calcium salt in spores is a problem which remains to be solved. The fast access of aldehydes into the cortex, mainly a result of gas plasma oxidation, may help blocking the amine groups of the 20 aspartic ~-semialdehyde thus interfering directly with the DPA synthesis.
The latter mechanism may explain why short exposures to a plasma gas in the presence of aldehydes can quickly destroy spores or their germinating capabilities. The 25 aldehydes seeding method of the present invention results in a shorter contact time in gas plasma to achieve a sporicidal effect, as compared with other gaseous phase sterilization procedures.
The cidal action of the low temperature aldehyde 9 ~ 32~ ~
seeded gas plasma is so fast sometimes, for example, less than ten minutes, that the possibility of inducing reactions inside the core or protoplast is rather small. The central portion of the spore is functionally a vegetative bud, which 5 contains the heriditary charter, a repressed protein synthe-sizing system, the enzymes necessary to initiate the synthesis of new enzymes and structural materials, and, presumably, reserves for the supply of energy intermediates. The modifi-cations taking place in the outer coats, cortex and plasma 10 membranes are sufficient to fully explain the cidal results obtained with the present invention. References above to the oxidation phenomena in a gas plasma are not restricted to the use of pure oxygen as an ionized gas but also includes the use of oxygen-containing gases like air, carbon dioxide and N2O.
15 Although not as fast as oxidizing plasmas, a noble gas, such as argon or helium, or nitrogen plasmas, can be seeded with aldehydes to decrease sterilization time.
The present invention, therefore, enables a con- ¦
siderable re~uction in sporekilling time to be achieved over the 20 values observed in conventional oxidizing and non-oxidizing gas plasmas. While excited ions, gas molecules, and photons modify the protective layers of the spores, active aldehyde radicals penetrate the changing structures and initiate many `
additional lethal reactions which accelerate the killing 25 process. A faster surface sterilization time results in a more economical process and provides the possibility to handle many highly heat sensitive materials, which may be degraded by prolonged exposure to the gas plasma, even at high tempera-tures below 100C. No severe corrosive or toxic residuals 30 are observed when adding aldehydes to a gas plasma.
1~0~3ZZ
To produce a gas plasma of the type required in the present invention, the carrier gas may be excited by one of two different radio-frequency methods. The first approach consists of a ring type or inductive discharge technique, 5 while the second method consists of a parallel plate or capa-citive discharge technique. The processing area consists always of a glass, plastic, or aluminum chamber maintained under subatmospheric pressure, generally 0.1 to 10 mm. of mercury, into which a controlled flow of gas and aldehyde 10 vapor is constantly moving under the continuous suction of a vacuum pump. To excite gases and vapors in the processing area, the radio-frequency energy delivered by a generator is coupled through an inductive coil wrapped around the pro-cessing chamber or by means of capacitive discharge plates 15 placed outside the chamber or chamber entrances. While in operation, the RF ~radio frequency) discharge glow can be made to extend virtually throughout the entire processing chamber. In some instances, the electrodes may be positioned in the processing chamber.
There are many ways to design electronic circuitry for maximizing RF energy coupling into the discharging gas.
Energy coupling optimization, which can reach up to 90%, can be achieved by matching the gas load impedance to the im-pedance of the ampli~ier plate output circuit and the tank 25 coil. The best impedance matching is achieved by a tuning process which consists of adjusting variable condensers in a low impedance matching network connected by coaxial cables between the reactor chamber and the generator. In more modern designs, the processing chamber and the relatively low power 110'132~ 1 11 i generator are coupled directly through high impedance connec-tors. This eliminates the complicated low impedance network and simplifies the electronic package. During power coupling to the gas plasma, a small amount of power is always lost 5 due to heating effects. There is also an amount of power reflected back to the generator. To know how efficiently one is discharging energy in the gas, a RF wattmeter is often in- !
serted in the electronic circuit to monitor the difference between forward and reflected power.
10Gas plasma generators operate generally around 13.5 Megahertz (MHz~ but frequencies in the range of 1 to 30 MHz also are satisfactory, and even may range up to 100 MHz.
The gas plasma may also be formed a~ higher fre-quencies in the microwave region, with frequencies ranging 15 from 100 to 300,000 MHz. A preferred microwave frequency from the practical viewpoint is 2450 MHz. In the microwave region, the atomic or excited molecular species have a longex life time than those formed at radio frequencies and they can persist downstream quite a distance into the glowless region.
20 This is an advantage from the analytical viewpoint, but it is also balanced by the more complicated and, therefore, more expensive electronic circuitry required. When using microwave gas excitation, the processing chamber is usually designed as a cavity, the generator is generally a magnetron type device 25 and the electro-magnetic energy is conveyed by standard wave guides.
Irrespective of the gas excitation frequency, it has been observed that the presence of small amounts of aldehyde vapors in the gas plasma considerably reduces the time 110~322 needed to kill sporulate~ and non-sporulated bacteri-a;
The invention is described further, by way of illus-tration, with reference to Figures 2 to 4 of the accompanying drawings, wherein:
Figure 2 is a schemati~ representation of an appara-tus for sterilizing various hospital type disposals in a semi-continuous manner;
Figures 3 and 3A are sectional views of the sterilizing chamber of Figure 2; and Figure 4 is a schematic representation of an alter-native form of sterilizing chamber using microwave frequencies.
Referring to the drawings, Figure 2 illustrates the elements of a low temperature seeded plasma (referred to later as LTSP) system used for sterilizing in a semi-continuous 15 manner various hospital type disposals. The system comprises a tunnel-like processing chamber 1, having a door 2 at each end, only the door 2 at the left-hand entrance side being shown. The disposables or non-disposables, for instance, pla.stic bottles of parenteral orophthalm~lo~ical solutions, 20 are loaded in the cylindrical tunnel chamber by means of a conventional automatic rail conveyor type system ~not shown).
After loading, the front and rear doors 2 are closed auto-matically by means of an electrically driven mechanical system 3. The loaded tunnel processing chamber 1 is then subjected 25 to vacuum to provide a subatmospheric pressure therein by means of a vacuum line system 4 connected to a trap 5 and to a vacuum pump 6. The subatmospheric pressure is generally about 0.1 to 10 mm. of mercury inside the entire processing chamber 1.
The gas to be ionized then is delivered from a com-pressed gas line or bottle 7, the pressure and flow rate being regulated by pressure gauges and by a constant flow rate membrane or needle valve 8. Aldehyde vapors are added to the , 5 gas flow from a container 9 by allowing the gas to bubble through liquid aldehyde and entrain the aldehyde vapors. A
flowmeter 10 is inserted between the aldehydes container 9 and the inlet into the tunnel chamber 1. The mixture of gas and vapor is delivered through a hollow pipe line 11 with 10 numerous small holes properly spaced for an even distribution into the tunnel chamber.
After evacuating most of the air in the tunnel chamber 1, the gas/vapor mixture is released in the processing area. The gas/aldehyde vapor flow is adjusted according to 15 the size and volume of the tunnel 1. The plasma formation is then initiated by proper impedance matching with inductive and capacitive controls, using an RF coil 12 which is part of an electrical circuit comprising a matching network 13, a power wattmeter 14 and an RF generator 15 converting AC
20 (alternating current) standard current into 13.5~ MHz high frequency. The RF generator 15 used for sustaining a plasma discharge should be capable of withstanding large variations in the load impedance, and essentially comprises a DC (direct current) power supply~ a crystal controlled RF oscillator and 25 a solid state buffer amplifier. Final amplification is accomplished by a power amplifier designed around a power tube to accommodate large variations in load impedance.
According to the typeof installation, a single inductive coil extending over the entire tunnel length may be driven s, ., from a single power generator or a series of smaller coil sections may be operated from smaller modular type RF genera-tors.
During RF excitation, continuous removal of gas 5 plasma flow is effected over the reaction time period required to achieve complete sterilization, usually between 5 and 20 minutes. The RF excitation is then automatically shut down, the gas flow is interrupted and the vacuum pump is stopped. Air is introduced automatically in the tunnel lO chamber 1 by a two-way valve 16. The two end doors are electro-mechanically opened and the samples container is automatically pulled out from the tunnel on a railing sliding system. The tunnel chamber l is then ready for sterilizing a new load. The entire sterilization cycle time generally 15 takes between lO and 30 minutes according to the type of processed material and power output level.
Figures 3 and 3a are more detailed sectional views of a longitudinal and lateral cross section, respectively, of a sterilizing tunnel type processing chamber 1, 2S shown in 20 Figure 2. The tunnel 17 is of cylindrical shape around a main axis and essentially consists of two concentric cylin-drical pipes 18 and l9 made of highly resistant inert material, such as, glass or a polymeric material, for exar;lple, a polysulfone, which are held by compression on end flanges 2~ with silicone type O-rings 20. After assembling the internal pipe l9 inside the external pipe 18, a hollow space ring 21 is created in which vacuum and subatmospheric pressure is pro-vided by vacuum pump suction through bottom openings 22. To permit a subatmospheric atmosphere to be formed around the 110~32Z
objects to be decorltaminated, slots or holes 23 are perforated at the bottom of the internal cylinder 19. The objects to be sterilized, for example, plastic bottles 24 of parenteral solutions, are placed in a basket of parallelepipedic shape 5 25, which slides over a rail track 25 on roller bearing equipped wheels 27. At the beginning of the sterilizing cycle, the front and end doors 28 and 29 are automatically opened by an electrically operated device 30 which rotates the door lB0 around the hinge 31. The front and end doors of 10 the tunnel are generally made of a dark ultraviolet absorb-ing polymeric material to prevent the dangerous photon emission from escaping from the chamber while allowing its maximum intensity of gas plasma glow to be observed. The circular O-rings 32 help to provide a good seal with the 15 doors against the ingress of external air. The mixture of reactive gas and aldehyde vapor is introduced in the process-ing tunnel through a small pipe 33 with perforated holes 34.
The small pipe for gas and vapor introduction enters the tunnel at one end and is positioned in the upper part of the 20 internal pipe 19 to allow uniform gas diffusion over the entire tunnel length. In Figure 3, the RF inductive coil 35 is wrapped aroun~ the main external body of the processing tunnel 17.
Figure 4 illustrates another embodiment of the in-25 vention utilizing the microwave frequencies range from 100 MHz to 300,0Q0 MHz~ The microwave gas plasma sterilizer shown in Figure 4 consists of a metal housing 35 quite similar to those used in conventional microwave ovens. Located within the housing are the main components of the low temperature micro-._ _ ,___,. ,,, , . , . . 1 ~ 10432Z6 wave gas plasma sys-tem, comprising a magnetron 36 which, by means of a transformer, rectifier, and magnetic field circuit contained in power pack 37, converts the AC current from the main power line 38 into microwave energy. The high power beam 5 o~ microwave energy, typically at 2450 MHz, is contained in a wave guide 39 and directed against the blades 40 of a fan 41 which rotates at a slow RPM (revolutions per minute). The fan reflects the power beam, bouncing it off the walls, ceiling, back and bottom of the oven cavity 42. At the 10 bottom of the oven cavity 42, a pyrex glass plate 43 trans-parent to microwaves is suspended approximately one inch above the metal bottom of the processing cavity. The instruments or material 44 to be surface sterilized are placed inside a gas tight sealed container 45 which is positioned in the oven 15 cavity 42 and rests upon the glass plate 43. The container 45 may be constructed of any material which is transparent to microwave energy, includlng polymeric materials, such as, poly-propylene, polyethylene, polystyrene and Teflon (trademark), carton board, paper or special glass composition. The 20 container 45 is of parallelepipedic shape with an upper lid 46 also made of microwave transparent material.
The lid 46 has two openings 47 and 4g, each with a stopcock or valve 49 and 50 to allow the formation of the gas/
aldehyde vapors mixture in a partial vacuum atmosphere of 25 pressure between 0.1 and 10 mm of mercury. The container 45 contains two trays 51 which support the items 44 to be sterilized, for example, the illustrated plastic bottles for ophthalmological solutions. The trays 51 are generally per-forated to allow a more uniform diffusion of the ionized gas ~, ~
3;~2 ~
l7 plasma. In the lower tray, a p]astic cup 52 is inscrted which contains the aldehyde solution 53 to be evaporated.
Due to the thermal effect of microwaves, the aldehyde solu-tion is gradually evaporated in the gas plasma when the micro- ' 5 wave energy is switched on. The carrier gas to be ionized is delivered to container 45 through opening 47 from a gas bottle (not shown) into a pressure line 54 which includes a constant flow valve 55, a pressure gauge 56, and, if desired, a flow-meter. The low pressure vacuum needed to empty the loaded 10 container 45 is created through opening 48 by vacuum line 57, which is connected to a trap 58 and to a vacuum pump 59.
A complete sterilizing cycle for the embodiment of Figure 4 is as follows: filling the trays 51 with the equip-ment to be decontaminated, introduction of the aldehyde solu-15 tion cup 52, air elimination by vacuum activation, introductionof the carrier gas, and switching on microwaves during the necessary time period, typically between 5 and 20 minutes, to maintain a continuous plasma flow. At the end of the exposure time, there is an automatic shut down of the 20 microwave generator 41, the carrier gas flow is also stopped and the vacuum is broken through the two way valve 60. The door of the microwave oven cavity 35 is then opened and the container 45 is removed after disconnecting the flexible tubings fastened to the stopcocks 49 and 50. The loaded con-25 tainer 45 can be maintained sterile, by the rapidly closingof the stopcocks 49 and 50, until there is a need to remove - the decontaminated equipment under aseptic conditions. An entire sterilization cycle generally lasts between 10 and 30 minutes. At no time during processin~ does the surface 30 temperature approach 100C. No de-aeration of the ,, 110~32Z
decontaminated equipment is needed since the oxidiæing plasma does not leave detectable traces of chemical on the treated surfaces.
The semicontinuous sterilizing process described 5 above with respect to the equipment shown in Figures 2, 3, 3A
and 4 can be adapted to deliver sterile instruments inside packages if the package is punctured by a small hole giving access to the ionized and excited gas mixture. At the end of the sterilization, the package can be removed under white 10 room conditions and a small sterile tape then applied to cover and seal the small hole. The sealing tape can be fastened manually or by an automatic machine.
The present invention can be applied to variable flow rates of different gases at different temperatures or 15 multiple pressures. Further, the structural details of the ; described apparatuses, the dimensions and shapes of their members, such as tunnel or cavity sizes, and their arrange-ments, for example, introducing aldehyde vapors in microwave field through evaporation or by a bubbler in the carrier gas 20 line, may be modified, and certain members may be replaced by other equivalent means, for example, RF coils may be replaced by capacitive plates and magnetrons may be replaced by klystrons or amplitron tubes, without departing from the scope of the invention.
The invention is illustrated by the following Examples. In these Examples, the sporicidal data presented was, in all instances, obtained according to the USDA (United States Department of Agriculture) approved fumigant sporicidal test method described in the Official Method of Analysis of 30 the Association of O~ficial Analytical Chemists (12th Ed., 19 1~0~322 Nov. 1975).
Two types o~ highly resistant strains o~ the following species: B. subtilis (ATCC 19659) and Cl. sporogenes (ATCC 3584), were used in the experiments. The spores carriers 5 were silk suture loops (L) and porcelain cylinders (C) which carried a dry ~ores load of 106 to 109 microorganisms. The spores carriers were individually suspended from a thin cotton thread attached to the gas pipe at the top of the pro-cessing chamber.
There was also added at the bottom of the processing chamber several spore test strips wrapped inside an 1/2 inch~hic~ surgical gauze. These control spore strips (American Sterilizer Co. "SPORDI" (Trademark) were made of Bacillus subtilis (globigii) and Bacillus stearothermophilus. The 15 subtilis strain was said to need a 60 minute exposure at 300F
for complete kill in dry heat while it required one hour and forty-five minutes at 130F to be destroyed in the presence of ethylene oxide gas concentration 600 mg. per liter, 50%
~elative humidity). In all the experiments, the vacuum 20 dried, acid resistant AOAC strains of B. subtilis and Cl.
sporogenes proved to be far more resistant than the SPORDI
spores and, for the sake o~ simplicity, the results of the SPORDI strips are not given in the data tables in the Examples.
25 Example 1 A series of experiments was conducted in a device as illustrated in Figure 2. The carrier gases used to form the plasma were pure oxygen, argon, and nitrogen. The aldehyde vapors added to the carrier gas were produced in a .
.. _, -- 110~322 bubbler with solutions of the following aldehydes: formalin ~-(8~ formaldehyde) acetaldehyde, glyoxal, malonaldehyde, propionaldehyde, succinaldehyde, butyraldehyde, glutaralde-hyde, 2-hydroxyadipaldehyde, crotonaldehyde, acrolein and 5 bcnzaldehyde~ The carrier gas flow rate was between ~0 cc.
and 100 cc. per minute at room temperature (about 20 to 25C).
The average internal pressure was 0.5 mm of mercury. The -emission frequency was 13.56 MHz and the average power density output in the plasma processing chamber was about 10 0.015 watts per cubic centimeter. The minimum amount of aldehydes maintained in the continuous gas plasma flow was about l~ mg per liter.
Table l below shows the results of experiments assessing the influence of exposure time with the various low 15 temperature aldehyde seeded plasmas. Control experiments consisted both of the gas alone (no aldehyde) and of a non-oxidizing plasma (hydrogen gas) with formaldehyde or glutar-a}dehyde vapors. For each type of sporulated bacteria on the specific carrier (loop or cylinder), .en samples were used.
20 In the tables, the results are shown on a "pass" or "fail"
basis respectively indicated by the letter "P", which denotes no growth in any of 10 samples, and "F", which denotes 1 to lO samples having bacterial growth a~ter proper culturing and heat shocking. For the sake of clarity, all 25 "fail" tests which preceeded the first "pass" tests were omitted since it is obvious that shorteE exposure times correspond to "fail" tests. As may be seen from the results of Table l, contact times between lO and 30 minutes can pro-vide satisfactory cidal action, the individual contact times 30 depending on the type of aldehyde vapor utilized.
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110~322 E~ample 2 Utiliziny the same experimental conditions as those of Example 1, except that the exposure time was maintained around 15 minutes while the power output was increased successively from 0.001 watts per cm of processing chamber to 0.015 to 0.1 watts per cm3, a further series of experiments was conducted.
AS may be seen from the results set forth in Table II below, no killing was achieved at the lowest power density, but excellent results were often obtained in the 0.015 to 0.1 watts per cm range. These results indicate the increased killing power which is attained by the addition of aldehyde traces in the gas plasma. Oxygen appeared the best carrier among the gases used in this series of experiments.
All"fail"tests which preceeded the first "pass" tests were omitted from Table II since it is obvious that lower power densities correspond to "fail" tests~
23 110~322 o '~ ~ C _ I ,V~ C r~ ~ C ~ ~ ~ ~ ~ L~ ' _~ o _~ ~ ~ C ~ _ C '` P, ~ s~.
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Example 3 In a further series of experiments, the aldehydes were vaporized from a 2% active ingredients solution and this corresponded roughly to a consumption of 15 cc. during a 15-5 minute run. However, when sampling the gas plasma, the concen-tration of aldehyde was found equal to 10 mg. per minute for a flow rate of 100 cc./min. This aldehyde concentration in the gas phase was roughly half the value to be expected from the va~orized aldehyde solution, indicating that approximately 10 half the active aldehydes was deposited on the wall of the processing chamber.
The concentrations of aldehyde recited in Table III
(below) are those observed in the gas plasma under normal operating conditions. As may be seen from the results, at 15 the lower level of 0.1 mg./min., no increase in sporicidal activity was observed with any of the three gases used in the tests. At the 1 mg./min. level, there were inconsistent results. At the 10 mg./min. level, most of the aldehydes boosted the sporicidal efficacy of the gas plasma. At the 20 100 mg./min. level, all aldehydes showed an increased spores killing over what was observed with the aldehydes alone or with a non-oxidizing gas, such as, hydrogen loaded with aldehydes.
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Example 4 Table IV (below) shows the results observed when replacing a single aldehyde composition by a mixture of two different aldehydes or by a mixed formula containing an 5 aldehyde with a non-aldehyde biocidal compound, i.e. phenol.
A mixed composition gave the same results as a single aldehyde solution as long as the total content in aldehydes remained the same in the two formulas. The presence of the phenol did not affect the aldehyde efficacy as a sporicidal 10 booster agent in the gas plasma.
Not reported on Table IV are a number of experiments conducted with various solutions of germicidal agents other than phenols. While maintaining the same concentration of aldehydes, there was added the following ingredients in equal 15 concentration: haloyen compounds, such as, chloroisocyanurates, for example, trichloro-S-triazinetrione and iodophors, for example, PVP-iodine complex; inorganic salts, for example, selenium sulfide; an alcoholic solution of zinc undecylenate;
ammonium quaternaries, such as, cetyl-pyridinium chloride;
20 organo sulfurs, such as, methylenebisthiocyanate and nitrogen compounds of fatty amines, such as N-alkyl trimethylene diamine. In no case was there detected a synergistic effect due to the presence of these agents in the vapor phase.
There was noted, however, a slight increase in activity 25 (additive effects) each time the plasma vaporization led to the dissociation of the chemical salt with a release of a halogen. The strong corrosive effect of ionized halogens was also observed and this renders impractical the use of such chemicals in a seeded low temperature plasma gas.
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A further set of experiments was conducted in the apparatus of Figure 4. Since these experiments were conducted at higher frequencies than is the case for Examples 1 to 4, the microwave glow discharge was more uniform inside an experimental polysulfone container. The gas plasma pressure (2mm. of mercury) was slightly higher than in previous tests because microwave discharges are more difficult to initiate and to sustain at low pressures (- 1 mm. of mercury) than DC or RF discharges.
Due to the higher longevity and efficacy of free radicals and ionized species in a microwave gas plasma, the contact time was reduced to 10 minutes. The plastic-polysulfone container transparent to microwaves had the following dimen-sions: 15 x 35 x 25 cms. (volume 16.37 liters). The averagedensity of the electromagnetic energy inside the resonant cavity of about 0.02 watts/cc was tuned at the nominal fre-quency of 2540 MHz (- 25 MHz). The gas flow rate was adjusted between 900 cc. and 1000 cc. per minute which corresponded to an average aldehyde content of 18 mg./min. in the plasma phase. During the 10 minutes processing, around 18 cc. of each aldehyde solution of 2~ concentration by weight was evaporated. This corresponded also to roughly twice the amount actually present for reaction in the gas plasma.
One may be seen from the results set forth in Table V, an increase in sporicidal ef~icacy results from the seeding of the small amount of aromatic, heterocyclic, saturated or unsaturated aldehydes in the electromagnetic continuous gas plasma discharge. When vaporizing furfural, the concentration -` 110~a3ZZ .
of this chemical in the oxygen flow stream was 0.0018~ by volume, since this chemical has a lower explosive limit in air of 2.1~ by volume. The 2~ aqueous solution was main-tained at all times during evaporation below the open cup 5 flash point of this aldehyde which is around 68C. Besides benzaldehyde, other aromatic aldehydes, such as, thiophen-aldehyde, and pyridine-2-aldehyde have qualitatively shown the same behavior.
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~:10~132Z
In summary of this disclosure, the present invention provides a plasma gas sterilization method having substanti.al advantages over prior gas phase sterilization procedures.
Modifi.cations are possible within the scope of this invention.
The average time needed to sterilize medical instruments in an ETO unit is 180 minutes at 30C., but it has to be followed by a long de-aeration period. For instance, the de-aeration time for medical devices is between 2 and 8 hours in a de-aerator machine, but it oscillates between 1 and 8 days at room temperature. On rubber gloves, the residues can burn the hands; on tubes carrying blood, they will damage red blood cells and cause hemolysis. Endo-tracheal tubes which are not properly aerated can causetracheitis or tissue necrosis.
Besides the risks due to the toxicity of ETO
residues, other accidents have been reported due to the ex-plosive characteristics of pure ETO. As little as 3%
ethylene oxide vapor in air will support combustion and will have explosive violence if confined. To solve this problem, various diluent gases such as CO~ or fluorinated hydro-carbons have been mixed with ETO in some commercial formulations.
It is apparent, therefore, that ETO sterilization became widely used not because it was an ideal sterilant, but rather since there seemed to be no alternative gas steri-lant method which was capable of as fast a sporicidal action without any drawbacks from the toxicological or environmental : 30 viewpoint.
~0~3Z2 The present invention provides an alternative to ETO sterilization with the advantages of faster sporicidal action, no de-aeration period, no toxic residue, and no explosion risk. Moreover, this invention provides a more 5 economical approach from the running and investment cost view-point when comparing the volume of material treated per unit of time.
In accordance with the present invention, there is provided a method of sterilizing a surface comprising con-10 tacting the surface with a low temperature gas plasma contain-ing at least 10 mg/l of an aldehyde under a subatmospheric pressure.
The term "Sterilization" as used herein refers to sporicidal action against Bacillus subtilis ATCC (American 15 Type Culture Collection) 19659 and Clostridrium sporogenes (ATCC 3584) because they are the resistan~ microorganisms used in the fumigant-sterilant test according to the requirements of the AOAC (Official Method of Analysis of the Association of Official Analytical Chemists, 12th ed., Nov. 1975).
20 The destruction of these two resistant species of spores by the AOAC procedure leads automatically to the destruction of other less resistant microorganisms, such as, mycobacteria, non-lipid and small viruses, lipid and medium size viruses, and vegetative bacteria.
A better understanding of the cidal mechanism of a low temperature gas plasma in accordance with this invention may be had by consideration of the physical structure of a highly resistant spore. Figure 1 represents the typical structure of a typical bacterial spore. The typical bacteria 30 spore is surrounded by an exosporium which is a loose sac 110~3Z2 peculiar to so~e spores species, and possesses, from the outside to the inside, successively, (a) multi-layered coats containing disulphide (-S-S-) rich proteins, (b) a thick cortex layer which contains the polymer murein (or peptido-5 glycan), (c) a plasma membrane, and (d) a core or sporeprotoplast.
The first line of resistance of the spore to exo-genous agents consists of the proteinaceous outer coats which contain keratin-like proteins. The stability of keratin 10 structures is due to frequent primary valence cross links (disulphide bonds) and secondary valence cross links (hydrogen bonds) between neighboring polypeptide chains. Keratin like proteins are typically strong, insoluble in aqueous salt solutions or in diluted acid and basic solutions, and are 15 resistant to proteolytic enzymes and hydrolysis. The layered outer coats, thus, are rather inert and play a predominant role in protecting the spore against exogenous agents. They seem to play an important role in cidal action through physical or chemical modifications which affect the diffusion 20 of cidal molecules, excited atoms or radicals inside the microorganism protoplast.
To alter the multilayered outer coats and thus allow further penetration and possible interactions in the critical cortex or protoplast regions, a very active agent mus be 25 chosen, and it has been found that an ionized gas plasma is an excellent vehicle to provide reactiYe atoms, free radicals, and molecules which will drastically alter the protective layers of bacteria, fungi, and spores. The presence of small amounts of aldehyde vapors in the ionized low tempera-llOi3~2 ture non-oxidizing gas plasma, in accordance with this inven- I
tion, leads to the destruction of sporulated and non- ¦
sporulated microorganisms.
In the present invention, the objects to be decon-5 taminated are exposed to a continuous flow of low temperaturegas plasma seeded with a small amount of an aldehyde, usually an aromatic, heterocyclic, saturated or unsaturated aldehyde.
The gas plasma is a partially ionized gas composed of ions, electrons, and neutral species.
The low temperature gas plasma is formed by gaseous electric discharges. In an electrical discharge, free elec-trons gain energy from the imposed electric field and lose this energy through collisions with neutral gas molecules.
The energy transfer process leads to the ormation of a 15 variety of highly reactive products including metastable atoms, free radicals, and ions.
For an ionized gas produced in an electrical dis-charge to be properly termed a "plasma", it must satisfy the requirement that the concentrations of positive and negative 20 charge carriers are approximately equal. The plasma used in the present invention are glow discharges plasma and are also termed "low temperature" gas plasma. This type of plasma is characterized by average electron energies of 1 to 10 eV and electron densities of 109 to 10 2 per cm . Contrary to the 25 conditions found in arcs or plasma jets, the electron and gas temperatures are very different due to the lack of thermal equilibrium. In a glow discharge, the electron temperature can be ten to a hundred times higher than the gas temperature.
The latter property is important when sterilizing the surfaces 30 of thermally sensitive materials.
, .
7 :1104322 r In the low temperature gas plasma used in this invention, there can be distinguished two types of reactive elements, i.e. those which consist of atoms, ions or free radicals and those which are small high energy particles 5 such as electrons and photons. In glow discharges a large amount of ultraviolet radiation (UV) is always present.
The UV high energy photons (3.3 to 6.2 eV) will produce strong cidal effects because they correspond to a maximum of absorption by DNA (deoxyribonucleic acid) and other nucleic 10 acids~ However, in the case of spores which can reach one millimeter in diameter, photon energy can be quickly dissipa-ted through the various spore layers and this may restrict photochemical reactions to outer coats. The photon energy is rather restricted to thin layer surface modifications and is, 15 therefore, more efficacious when dealing with the smaller non-sporulated bacteria. In the case of high resistance spores, the photonic action may contribute to partial alteration of the disulphide rich proteins coat and thus facilitate the diffusion of free radicals, atoms, or excite~molecules inside 20 the core region.
In the present invention, small amounts of vaporized aldehyde monomers and free radicals present in a low tempera-ture gas plasma can greatly increase the overall biocidal action of a gas plasma.
The exact mechanism whereby enhanced sporicidal activity is attained using the aldehyde-seeded plasma stream is not fully understood, but some mechanis~ can be considered.
For example, due to the presence of atomic or excited oxygen in the gas phase, the aldehydes may produce short life very 30 reactive epoxides and other intermediates and free radicals ~10~322 which may interact with many proteins and nucleic acids groups in outer layer coats and thereby improve diffusion of cidal groups.
The next possible step in the diffusion of cidal 5 groups is the penetration inside the cortex layer whose major component is the polymer murein (or peptidoglycan).
Murein is a large, crosslinked, net-like molecule. A con-jugat~d attack by atomic oxygen and aldehyde radicals on the polymer rapidly shakes and modifies the tight polymer 10 structuxe of the cortex layer, leading to its destruction.
In addition, there is the potential for alteration of the hypothetical pathway of dipicolinic acid synthesis by the aldehydes. It has long been speculated that since calcium and dipicolinic acid (DPA) occur in spores in roughly equimolar lS amounts, they form a salt complex whose role is capital in spores resistance. The exact location of the calcium salt in spores is a problem which remains to be solved. The fast access of aldehydes into the cortex, mainly a result of gas plasma oxidation, may help blocking the amine groups of the 20 aspartic ~-semialdehyde thus interfering directly with the DPA synthesis.
The latter mechanism may explain why short exposures to a plasma gas in the presence of aldehydes can quickly destroy spores or their germinating capabilities. The 25 aldehydes seeding method of the present invention results in a shorter contact time in gas plasma to achieve a sporicidal effect, as compared with other gaseous phase sterilization procedures.
The cidal action of the low temperature aldehyde 9 ~ 32~ ~
seeded gas plasma is so fast sometimes, for example, less than ten minutes, that the possibility of inducing reactions inside the core or protoplast is rather small. The central portion of the spore is functionally a vegetative bud, which 5 contains the heriditary charter, a repressed protein synthe-sizing system, the enzymes necessary to initiate the synthesis of new enzymes and structural materials, and, presumably, reserves for the supply of energy intermediates. The modifi-cations taking place in the outer coats, cortex and plasma 10 membranes are sufficient to fully explain the cidal results obtained with the present invention. References above to the oxidation phenomena in a gas plasma are not restricted to the use of pure oxygen as an ionized gas but also includes the use of oxygen-containing gases like air, carbon dioxide and N2O.
15 Although not as fast as oxidizing plasmas, a noble gas, such as argon or helium, or nitrogen plasmas, can be seeded with aldehydes to decrease sterilization time.
The present invention, therefore, enables a con- ¦
siderable re~uction in sporekilling time to be achieved over the 20 values observed in conventional oxidizing and non-oxidizing gas plasmas. While excited ions, gas molecules, and photons modify the protective layers of the spores, active aldehyde radicals penetrate the changing structures and initiate many `
additional lethal reactions which accelerate the killing 25 process. A faster surface sterilization time results in a more economical process and provides the possibility to handle many highly heat sensitive materials, which may be degraded by prolonged exposure to the gas plasma, even at high tempera-tures below 100C. No severe corrosive or toxic residuals 30 are observed when adding aldehydes to a gas plasma.
1~0~3ZZ
To produce a gas plasma of the type required in the present invention, the carrier gas may be excited by one of two different radio-frequency methods. The first approach consists of a ring type or inductive discharge technique, 5 while the second method consists of a parallel plate or capa-citive discharge technique. The processing area consists always of a glass, plastic, or aluminum chamber maintained under subatmospheric pressure, generally 0.1 to 10 mm. of mercury, into which a controlled flow of gas and aldehyde 10 vapor is constantly moving under the continuous suction of a vacuum pump. To excite gases and vapors in the processing area, the radio-frequency energy delivered by a generator is coupled through an inductive coil wrapped around the pro-cessing chamber or by means of capacitive discharge plates 15 placed outside the chamber or chamber entrances. While in operation, the RF ~radio frequency) discharge glow can be made to extend virtually throughout the entire processing chamber. In some instances, the electrodes may be positioned in the processing chamber.
There are many ways to design electronic circuitry for maximizing RF energy coupling into the discharging gas.
Energy coupling optimization, which can reach up to 90%, can be achieved by matching the gas load impedance to the im-pedance of the ampli~ier plate output circuit and the tank 25 coil. The best impedance matching is achieved by a tuning process which consists of adjusting variable condensers in a low impedance matching network connected by coaxial cables between the reactor chamber and the generator. In more modern designs, the processing chamber and the relatively low power 110'132~ 1 11 i generator are coupled directly through high impedance connec-tors. This eliminates the complicated low impedance network and simplifies the electronic package. During power coupling to the gas plasma, a small amount of power is always lost 5 due to heating effects. There is also an amount of power reflected back to the generator. To know how efficiently one is discharging energy in the gas, a RF wattmeter is often in- !
serted in the electronic circuit to monitor the difference between forward and reflected power.
10Gas plasma generators operate generally around 13.5 Megahertz (MHz~ but frequencies in the range of 1 to 30 MHz also are satisfactory, and even may range up to 100 MHz.
The gas plasma may also be formed a~ higher fre-quencies in the microwave region, with frequencies ranging 15 from 100 to 300,000 MHz. A preferred microwave frequency from the practical viewpoint is 2450 MHz. In the microwave region, the atomic or excited molecular species have a longex life time than those formed at radio frequencies and they can persist downstream quite a distance into the glowless region.
20 This is an advantage from the analytical viewpoint, but it is also balanced by the more complicated and, therefore, more expensive electronic circuitry required. When using microwave gas excitation, the processing chamber is usually designed as a cavity, the generator is generally a magnetron type device 25 and the electro-magnetic energy is conveyed by standard wave guides.
Irrespective of the gas excitation frequency, it has been observed that the presence of small amounts of aldehyde vapors in the gas plasma considerably reduces the time 110~322 needed to kill sporulate~ and non-sporulated bacteri-a;
The invention is described further, by way of illus-tration, with reference to Figures 2 to 4 of the accompanying drawings, wherein:
Figure 2 is a schemati~ representation of an appara-tus for sterilizing various hospital type disposals in a semi-continuous manner;
Figures 3 and 3A are sectional views of the sterilizing chamber of Figure 2; and Figure 4 is a schematic representation of an alter-native form of sterilizing chamber using microwave frequencies.
Referring to the drawings, Figure 2 illustrates the elements of a low temperature seeded plasma (referred to later as LTSP) system used for sterilizing in a semi-continuous 15 manner various hospital type disposals. The system comprises a tunnel-like processing chamber 1, having a door 2 at each end, only the door 2 at the left-hand entrance side being shown. The disposables or non-disposables, for instance, pla.stic bottles of parenteral orophthalm~lo~ical solutions, 20 are loaded in the cylindrical tunnel chamber by means of a conventional automatic rail conveyor type system ~not shown).
After loading, the front and rear doors 2 are closed auto-matically by means of an electrically driven mechanical system 3. The loaded tunnel processing chamber 1 is then subjected 25 to vacuum to provide a subatmospheric pressure therein by means of a vacuum line system 4 connected to a trap 5 and to a vacuum pump 6. The subatmospheric pressure is generally about 0.1 to 10 mm. of mercury inside the entire processing chamber 1.
The gas to be ionized then is delivered from a com-pressed gas line or bottle 7, the pressure and flow rate being regulated by pressure gauges and by a constant flow rate membrane or needle valve 8. Aldehyde vapors are added to the , 5 gas flow from a container 9 by allowing the gas to bubble through liquid aldehyde and entrain the aldehyde vapors. A
flowmeter 10 is inserted between the aldehydes container 9 and the inlet into the tunnel chamber 1. The mixture of gas and vapor is delivered through a hollow pipe line 11 with 10 numerous small holes properly spaced for an even distribution into the tunnel chamber.
After evacuating most of the air in the tunnel chamber 1, the gas/vapor mixture is released in the processing area. The gas/aldehyde vapor flow is adjusted according to 15 the size and volume of the tunnel 1. The plasma formation is then initiated by proper impedance matching with inductive and capacitive controls, using an RF coil 12 which is part of an electrical circuit comprising a matching network 13, a power wattmeter 14 and an RF generator 15 converting AC
20 (alternating current) standard current into 13.5~ MHz high frequency. The RF generator 15 used for sustaining a plasma discharge should be capable of withstanding large variations in the load impedance, and essentially comprises a DC (direct current) power supply~ a crystal controlled RF oscillator and 25 a solid state buffer amplifier. Final amplification is accomplished by a power amplifier designed around a power tube to accommodate large variations in load impedance.
According to the typeof installation, a single inductive coil extending over the entire tunnel length may be driven s, ., from a single power generator or a series of smaller coil sections may be operated from smaller modular type RF genera-tors.
During RF excitation, continuous removal of gas 5 plasma flow is effected over the reaction time period required to achieve complete sterilization, usually between 5 and 20 minutes. The RF excitation is then automatically shut down, the gas flow is interrupted and the vacuum pump is stopped. Air is introduced automatically in the tunnel lO chamber 1 by a two-way valve 16. The two end doors are electro-mechanically opened and the samples container is automatically pulled out from the tunnel on a railing sliding system. The tunnel chamber l is then ready for sterilizing a new load. The entire sterilization cycle time generally 15 takes between lO and 30 minutes according to the type of processed material and power output level.
Figures 3 and 3a are more detailed sectional views of a longitudinal and lateral cross section, respectively, of a sterilizing tunnel type processing chamber 1, 2S shown in 20 Figure 2. The tunnel 17 is of cylindrical shape around a main axis and essentially consists of two concentric cylin-drical pipes 18 and l9 made of highly resistant inert material, such as, glass or a polymeric material, for exar;lple, a polysulfone, which are held by compression on end flanges 2~ with silicone type O-rings 20. After assembling the internal pipe l9 inside the external pipe 18, a hollow space ring 21 is created in which vacuum and subatmospheric pressure is pro-vided by vacuum pump suction through bottom openings 22. To permit a subatmospheric atmosphere to be formed around the 110~32Z
objects to be decorltaminated, slots or holes 23 are perforated at the bottom of the internal cylinder 19. The objects to be sterilized, for example, plastic bottles 24 of parenteral solutions, are placed in a basket of parallelepipedic shape 5 25, which slides over a rail track 25 on roller bearing equipped wheels 27. At the beginning of the sterilizing cycle, the front and end doors 28 and 29 are automatically opened by an electrically operated device 30 which rotates the door lB0 around the hinge 31. The front and end doors of 10 the tunnel are generally made of a dark ultraviolet absorb-ing polymeric material to prevent the dangerous photon emission from escaping from the chamber while allowing its maximum intensity of gas plasma glow to be observed. The circular O-rings 32 help to provide a good seal with the 15 doors against the ingress of external air. The mixture of reactive gas and aldehyde vapor is introduced in the process-ing tunnel through a small pipe 33 with perforated holes 34.
The small pipe for gas and vapor introduction enters the tunnel at one end and is positioned in the upper part of the 20 internal pipe 19 to allow uniform gas diffusion over the entire tunnel length. In Figure 3, the RF inductive coil 35 is wrapped aroun~ the main external body of the processing tunnel 17.
Figure 4 illustrates another embodiment of the in-25 vention utilizing the microwave frequencies range from 100 MHz to 300,0Q0 MHz~ The microwave gas plasma sterilizer shown in Figure 4 consists of a metal housing 35 quite similar to those used in conventional microwave ovens. Located within the housing are the main components of the low temperature micro-._ _ ,___,. ,,, , . , . . 1 ~ 10432Z6 wave gas plasma sys-tem, comprising a magnetron 36 which, by means of a transformer, rectifier, and magnetic field circuit contained in power pack 37, converts the AC current from the main power line 38 into microwave energy. The high power beam 5 o~ microwave energy, typically at 2450 MHz, is contained in a wave guide 39 and directed against the blades 40 of a fan 41 which rotates at a slow RPM (revolutions per minute). The fan reflects the power beam, bouncing it off the walls, ceiling, back and bottom of the oven cavity 42. At the 10 bottom of the oven cavity 42, a pyrex glass plate 43 trans-parent to microwaves is suspended approximately one inch above the metal bottom of the processing cavity. The instruments or material 44 to be surface sterilized are placed inside a gas tight sealed container 45 which is positioned in the oven 15 cavity 42 and rests upon the glass plate 43. The container 45 may be constructed of any material which is transparent to microwave energy, includlng polymeric materials, such as, poly-propylene, polyethylene, polystyrene and Teflon (trademark), carton board, paper or special glass composition. The 20 container 45 is of parallelepipedic shape with an upper lid 46 also made of microwave transparent material.
The lid 46 has two openings 47 and 4g, each with a stopcock or valve 49 and 50 to allow the formation of the gas/
aldehyde vapors mixture in a partial vacuum atmosphere of 25 pressure between 0.1 and 10 mm of mercury. The container 45 contains two trays 51 which support the items 44 to be sterilized, for example, the illustrated plastic bottles for ophthalmological solutions. The trays 51 are generally per-forated to allow a more uniform diffusion of the ionized gas ~, ~
3;~2 ~
l7 plasma. In the lower tray, a p]astic cup 52 is inscrted which contains the aldehyde solution 53 to be evaporated.
Due to the thermal effect of microwaves, the aldehyde solu-tion is gradually evaporated in the gas plasma when the micro- ' 5 wave energy is switched on. The carrier gas to be ionized is delivered to container 45 through opening 47 from a gas bottle (not shown) into a pressure line 54 which includes a constant flow valve 55, a pressure gauge 56, and, if desired, a flow-meter. The low pressure vacuum needed to empty the loaded 10 container 45 is created through opening 48 by vacuum line 57, which is connected to a trap 58 and to a vacuum pump 59.
A complete sterilizing cycle for the embodiment of Figure 4 is as follows: filling the trays 51 with the equip-ment to be decontaminated, introduction of the aldehyde solu-15 tion cup 52, air elimination by vacuum activation, introductionof the carrier gas, and switching on microwaves during the necessary time period, typically between 5 and 20 minutes, to maintain a continuous plasma flow. At the end of the exposure time, there is an automatic shut down of the 20 microwave generator 41, the carrier gas flow is also stopped and the vacuum is broken through the two way valve 60. The door of the microwave oven cavity 35 is then opened and the container 45 is removed after disconnecting the flexible tubings fastened to the stopcocks 49 and 50. The loaded con-25 tainer 45 can be maintained sterile, by the rapidly closingof the stopcocks 49 and 50, until there is a need to remove - the decontaminated equipment under aseptic conditions. An entire sterilization cycle generally lasts between 10 and 30 minutes. At no time during processin~ does the surface 30 temperature approach 100C. No de-aeration of the ,, 110~32Z
decontaminated equipment is needed since the oxidiæing plasma does not leave detectable traces of chemical on the treated surfaces.
The semicontinuous sterilizing process described 5 above with respect to the equipment shown in Figures 2, 3, 3A
and 4 can be adapted to deliver sterile instruments inside packages if the package is punctured by a small hole giving access to the ionized and excited gas mixture. At the end of the sterilization, the package can be removed under white 10 room conditions and a small sterile tape then applied to cover and seal the small hole. The sealing tape can be fastened manually or by an automatic machine.
The present invention can be applied to variable flow rates of different gases at different temperatures or 15 multiple pressures. Further, the structural details of the ; described apparatuses, the dimensions and shapes of their members, such as tunnel or cavity sizes, and their arrange-ments, for example, introducing aldehyde vapors in microwave field through evaporation or by a bubbler in the carrier gas 20 line, may be modified, and certain members may be replaced by other equivalent means, for example, RF coils may be replaced by capacitive plates and magnetrons may be replaced by klystrons or amplitron tubes, without departing from the scope of the invention.
The invention is illustrated by the following Examples. In these Examples, the sporicidal data presented was, in all instances, obtained according to the USDA (United States Department of Agriculture) approved fumigant sporicidal test method described in the Official Method of Analysis of 30 the Association of O~ficial Analytical Chemists (12th Ed., 19 1~0~322 Nov. 1975).
Two types o~ highly resistant strains o~ the following species: B. subtilis (ATCC 19659) and Cl. sporogenes (ATCC 3584), were used in the experiments. The spores carriers 5 were silk suture loops (L) and porcelain cylinders (C) which carried a dry ~ores load of 106 to 109 microorganisms. The spores carriers were individually suspended from a thin cotton thread attached to the gas pipe at the top of the pro-cessing chamber.
There was also added at the bottom of the processing chamber several spore test strips wrapped inside an 1/2 inch~hic~ surgical gauze. These control spore strips (American Sterilizer Co. "SPORDI" (Trademark) were made of Bacillus subtilis (globigii) and Bacillus stearothermophilus. The 15 subtilis strain was said to need a 60 minute exposure at 300F
for complete kill in dry heat while it required one hour and forty-five minutes at 130F to be destroyed in the presence of ethylene oxide gas concentration 600 mg. per liter, 50%
~elative humidity). In all the experiments, the vacuum 20 dried, acid resistant AOAC strains of B. subtilis and Cl.
sporogenes proved to be far more resistant than the SPORDI
spores and, for the sake o~ simplicity, the results of the SPORDI strips are not given in the data tables in the Examples.
25 Example 1 A series of experiments was conducted in a device as illustrated in Figure 2. The carrier gases used to form the plasma were pure oxygen, argon, and nitrogen. The aldehyde vapors added to the carrier gas were produced in a .
.. _, -- 110~322 bubbler with solutions of the following aldehydes: formalin ~-(8~ formaldehyde) acetaldehyde, glyoxal, malonaldehyde, propionaldehyde, succinaldehyde, butyraldehyde, glutaralde-hyde, 2-hydroxyadipaldehyde, crotonaldehyde, acrolein and 5 bcnzaldehyde~ The carrier gas flow rate was between ~0 cc.
and 100 cc. per minute at room temperature (about 20 to 25C).
The average internal pressure was 0.5 mm of mercury. The -emission frequency was 13.56 MHz and the average power density output in the plasma processing chamber was about 10 0.015 watts per cubic centimeter. The minimum amount of aldehydes maintained in the continuous gas plasma flow was about l~ mg per liter.
Table l below shows the results of experiments assessing the influence of exposure time with the various low 15 temperature aldehyde seeded plasmas. Control experiments consisted both of the gas alone (no aldehyde) and of a non-oxidizing plasma (hydrogen gas) with formaldehyde or glutar-a}dehyde vapors. For each type of sporulated bacteria on the specific carrier (loop or cylinder), .en samples were used.
20 In the tables, the results are shown on a "pass" or "fail"
basis respectively indicated by the letter "P", which denotes no growth in any of 10 samples, and "F", which denotes 1 to lO samples having bacterial growth a~ter proper culturing and heat shocking. For the sake of clarity, all 25 "fail" tests which preceeded the first "pass" tests were omitted since it is obvious that shorteE exposure times correspond to "fail" tests. As may be seen from the results of Table l, contact times between lO and 30 minutes can pro-vide satisfactory cidal action, the individual contact times 30 depending on the type of aldehyde vapor utilized.
,, ' ~
,: .
liO4322 ~ 0~ . ~ ,, L~
'J ~ G C C f~ 4 _ ~ ~ ~ k~ ~ C LL C_ p~
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ffl ~ c> c E V O O ~ U ~ V O ~
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110~322 E~ample 2 Utiliziny the same experimental conditions as those of Example 1, except that the exposure time was maintained around 15 minutes while the power output was increased successively from 0.001 watts per cm of processing chamber to 0.015 to 0.1 watts per cm3, a further series of experiments was conducted.
AS may be seen from the results set forth in Table II below, no killing was achieved at the lowest power density, but excellent results were often obtained in the 0.015 to 0.1 watts per cm range. These results indicate the increased killing power which is attained by the addition of aldehyde traces in the gas plasma. Oxygen appeared the best carrier among the gases used in this series of experiments.
All"fail"tests which preceeded the first "pass" tests were omitted from Table II since it is obvious that lower power densities correspond to "fail" tests~
23 110~322 o '~ ~ C _ I ,V~ C r~ ~ C ~ ~ ~ ~ ~ L~ ' _~ o _~ ~ ~ C ~ _ C '` P, ~ s~.
Z _ ~.
o U _ ~ V'u C C~. ~ D. ~
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o o_~ C~ .
~ L~ ~ ~ ~ uA ~ ~ a. ~ u. c~.
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e . ~
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_ ~ _ _ __ . Vl ., O ~ . ~ ~
~ o CO~ ~ ~ D.
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110~32Z
Example 3 In a further series of experiments, the aldehydes were vaporized from a 2% active ingredients solution and this corresponded roughly to a consumption of 15 cc. during a 15-5 minute run. However, when sampling the gas plasma, the concen-tration of aldehyde was found equal to 10 mg. per minute for a flow rate of 100 cc./min. This aldehyde concentration in the gas phase was roughly half the value to be expected from the va~orized aldehyde solution, indicating that approximately 10 half the active aldehydes was deposited on the wall of the processing chamber.
The concentrations of aldehyde recited in Table III
(below) are those observed in the gas plasma under normal operating conditions. As may be seen from the results, at 15 the lower level of 0.1 mg./min., no increase in sporicidal activity was observed with any of the three gases used in the tests. At the 1 mg./min. level, there were inconsistent results. At the 10 mg./min. level, most of the aldehydes boosted the sporicidal efficacy of the gas plasma. At the 20 100 mg./min. level, all aldehydes showed an increased spores killing over what was observed with the aldehydes alone or with a non-oxidizing gas, such as, hydrogen loaded with aldehydes.
,, . . .
-` 110~3Z2 u~ 25 O co~ C. C. C. ~ ~D. C~. ~ L.
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C~ LL Q. 1~ C~
t~
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_ 0~ ' C L~ .
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. _ _ ~) a. ~ ~ ~ ~
l o ~, ~ c~ ,.~ ~
! _t D ~ Q.. ~ D. ~ ~ t~. 1~ Cl~ t-, a. ~ r~
. 3 t~ C~
l -o~
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O ~0~ D. ~ D~Q. ~U.
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H O O y Cl. ~ ~ 1~ t~ ~ C~. ~ ~ D.
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l . O _O ~D. C~. n~ ~ ~ c~ D~ U~ ~ e~. tL
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Example 4 Table IV (below) shows the results observed when replacing a single aldehyde composition by a mixture of two different aldehydes or by a mixed formula containing an 5 aldehyde with a non-aldehyde biocidal compound, i.e. phenol.
A mixed composition gave the same results as a single aldehyde solution as long as the total content in aldehydes remained the same in the two formulas. The presence of the phenol did not affect the aldehyde efficacy as a sporicidal 10 booster agent in the gas plasma.
Not reported on Table IV are a number of experiments conducted with various solutions of germicidal agents other than phenols. While maintaining the same concentration of aldehydes, there was added the following ingredients in equal 15 concentration: haloyen compounds, such as, chloroisocyanurates, for example, trichloro-S-triazinetrione and iodophors, for example, PVP-iodine complex; inorganic salts, for example, selenium sulfide; an alcoholic solution of zinc undecylenate;
ammonium quaternaries, such as, cetyl-pyridinium chloride;
20 organo sulfurs, such as, methylenebisthiocyanate and nitrogen compounds of fatty amines, such as N-alkyl trimethylene diamine. In no case was there detected a synergistic effect due to the presence of these agents in the vapor phase.
There was noted, however, a slight increase in activity 25 (additive effects) each time the plasma vaporization led to the dissociation of the chemical salt with a release of a halogen. The strong corrosive effect of ionized halogens was also observed and this renders impractical the use of such chemicals in a seeded low temperature plasma gas.
... .
, . . ... . .
~ ~ t~ tl. C~. tl~ 1~
Z 0~, .
O t~_1 t` t~. tl. t. t~4 . ~
~ _ _ _ , I l Z
- e ~) t_ C~. t~ D.. CL _ _ O .
Z D~ .
O t~1 tb C~ t~ LL _ ._ _I~ t` CL CL C~, tL 12., :~ ~.
~i _ . ~ t` t~ t t~A _ ~A_ ,_ A ~) Cl. CL tA. t ti. t2,, ~3 Z h 1~ ~
~3. a.e~Lel.~- .
- . _. ~ _ .. _.. __ ~ .C~ 'O . ~
C ~ h E~ "OA v~Ul W E .~j V ~ ~ ~
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~4 ~ _ ~ S ~
o ~ :~ t t, ~ ~ ~0 A , ~ U :~ ` e .. . . _ . . . . . . .
''- - .
28 ~ 322 Example 5 I
A further set of experiments was conducted in the apparatus of Figure 4. Since these experiments were conducted at higher frequencies than is the case for Examples 1 to 4, the microwave glow discharge was more uniform inside an experimental polysulfone container. The gas plasma pressure (2mm. of mercury) was slightly higher than in previous tests because microwave discharges are more difficult to initiate and to sustain at low pressures (- 1 mm. of mercury) than DC or RF discharges.
Due to the higher longevity and efficacy of free radicals and ionized species in a microwave gas plasma, the contact time was reduced to 10 minutes. The plastic-polysulfone container transparent to microwaves had the following dimen-sions: 15 x 35 x 25 cms. (volume 16.37 liters). The averagedensity of the electromagnetic energy inside the resonant cavity of about 0.02 watts/cc was tuned at the nominal fre-quency of 2540 MHz (- 25 MHz). The gas flow rate was adjusted between 900 cc. and 1000 cc. per minute which corresponded to an average aldehyde content of 18 mg./min. in the plasma phase. During the 10 minutes processing, around 18 cc. of each aldehyde solution of 2~ concentration by weight was evaporated. This corresponded also to roughly twice the amount actually present for reaction in the gas plasma.
One may be seen from the results set forth in Table V, an increase in sporicidal ef~icacy results from the seeding of the small amount of aromatic, heterocyclic, saturated or unsaturated aldehydes in the electromagnetic continuous gas plasma discharge. When vaporizing furfural, the concentration -` 110~a3ZZ .
of this chemical in the oxygen flow stream was 0.0018~ by volume, since this chemical has a lower explosive limit in air of 2.1~ by volume. The 2~ aqueous solution was main-tained at all times during evaporation below the open cup 5 flash point of this aldehyde which is around 68C. Besides benzaldehyde, other aromatic aldehydes, such as, thiophen-aldehyde, and pyridine-2-aldehyde have qualitatively shown the same behavior.
C 30 110~3ZZ
o ~ ~ ' Z ~ _1 r, C~ ~ 1~
O ~1 .
~_ V~
Z ~
~ ~ ~ C ~ ~ C ~ C~ ~ ~ ~ U~
~ _~ CL~Cn.~ ~
~ __ ~ .
O ~ c ~. c c~ ~. a., Q. ~ ~
l Z D. ~ ~ ~
i ~ ~ .
I eS~ Ul . c~. c ~ ~ ~ a. c~ . P CL Cl~
3c~ , u., . .A _ ._ ~ O . ~~
h ~ G C~ . C 1~ . ~ 1~.
Z G ~ C C ~ Q. ~ G D~ .~ C~ G ~4 U~
O ~ -~ ~ ^ C C~ . ~ C Cl. ~ ~: ~ 2. ~L
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l ~ .~ ~ C~ ~ 0~ D. a ~ o l ~ 0 ~0 .C --~ ~ ' .~ ~ ~ C -- C~ .
~ ~ a o ~ ~ ~
o ~ ~ I 0~ h_4 o ~ ~ i~ ~ .
C~ _ ~ E J O O C~ ~ ~i; .
G ~ ~ ~ ~ ~ O ~ v ~ _ h O t ~!I J~t ~ ~ ~ ~ 2 r r ~ ~ U ~ ~ t~
~:10~132Z
In summary of this disclosure, the present invention provides a plasma gas sterilization method having substanti.al advantages over prior gas phase sterilization procedures.
Modifi.cations are possible within the scope of this invention.
Claims
The embodiments of the invention in which an exclu-sive property or privilege is claimed are defined as follows:
1. A method of sterilizing a surface comprising contacting said surface with a low temperature gas plasma containing at least 10 mg/l of an aldehyde under subatmospheric pressure.
2. A method in accordance with Claim 1 wherein the aldehyde is at least one member selected from the group consisting of aromatic, heterocyclic and saturated and unsaturated acyclic aldehydes.
3. A method in accordance with Claim 1 wherein said gas plasma is produced from electromagnetic excitation of at least one gas selected from the group consisting of oxygen, argon, helium, nitrogen, carbon dioxide and nitrogen oxide.
4. A method in accordance with Claim 1 wherein the pressure of said gas plasma is equal to or greater that 0.1mm. of mercury.
5. A method in accordance with Claim 1 wherein said gas plasma is produced by gaseous electromagnetic discharges in the 1 to 100 MHz radio frequency region.
6. A method in accordance with Claim 1 wherein said gas plasma is produced by gaseous electromagnetic discharges in the 100 to 300,000 MHz microwave range.
7. A method in accordance with Claim 1 wherein said gas plasma is confined inside a fluid-tight container or chamber into which the electromagnetic field density is at least equal to 0.001 watts per cubic centimeter of space.
9. A method in accordance with Claim 1 wherein said gas plasma contains at least one aldehyde selected from the group consisting of formaldehyde, acetaldehyde, glyoxal, malonaldehyde, propionaldehyde, succinaldehyde, butyraldehyde, glutaraldehyde, 2-hydroxyadipaldehyde, acrolein, crotonal-dehyde, benzaldehyde, and 2-furaldehyde.
10. A method in accordance with Claim 1 wherein the aldehyde vapors are introduced in a continuously produced gas plasma upstream in a carrier gas flow.
11. A method in accordance with Claim 1 wherein the aldehyde vapors are introduced in a continuously produced gas plasma inside a plasma processing chamber itself.
12. A method of sterilizing surfaces, comprising:
(a) placing the surface to be sterilized in a fluid-tight chamber;
(b) evacuating said chamber to a pressure equal to or greater than 0.1mm. of mercury;
(c) introducing into the evacuated chamber a gas containing at least ten milligrams per liter of at least one vaporized aldehyde selected from the group consisting of aromatic, heterocyclic and saturated and unsaturated acyclic aldehydes per liter of gas plasma;
(d) establishing an electromagnetic field in the 1 to 10, 000 MHz range with an average spatial density of energy of at least 0.001 watts per cubic centimeter of chamber;
(e) maintaining the abovementioned electromagnetic field for a time long enough to completely destroy all living microorganisms while not affecting the physical or chemical properties of the object to be decontaminated.
13. A method in accordance with Claim 1 wherein said gas plasma will also contain in an amount equal to or greater than ten milligrams per liter of said gas plasma of at least one vaporized biocidal agent selected from the group consisting of phenols, halogens, inorganic and organic metallic salts, organosulfur and nitrogen compounds.
1. A method of sterilizing a surface comprising contacting said surface with a low temperature gas plasma containing at least 10 mg/l of an aldehyde under subatmospheric pressure.
2. A method in accordance with Claim 1 wherein the aldehyde is at least one member selected from the group consisting of aromatic, heterocyclic and saturated and unsaturated acyclic aldehydes.
3. A method in accordance with Claim 1 wherein said gas plasma is produced from electromagnetic excitation of at least one gas selected from the group consisting of oxygen, argon, helium, nitrogen, carbon dioxide and nitrogen oxide.
4. A method in accordance with Claim 1 wherein the pressure of said gas plasma is equal to or greater that 0.1mm. of mercury.
5. A method in accordance with Claim 1 wherein said gas plasma is produced by gaseous electromagnetic discharges in the 1 to 100 MHz radio frequency region.
6. A method in accordance with Claim 1 wherein said gas plasma is produced by gaseous electromagnetic discharges in the 100 to 300,000 MHz microwave range.
7. A method in accordance with Claim 1 wherein said gas plasma is confined inside a fluid-tight container or chamber into which the electromagnetic field density is at least equal to 0.001 watts per cubic centimeter of space.
9. A method in accordance with Claim 1 wherein said gas plasma contains at least one aldehyde selected from the group consisting of formaldehyde, acetaldehyde, glyoxal, malonaldehyde, propionaldehyde, succinaldehyde, butyraldehyde, glutaraldehyde, 2-hydroxyadipaldehyde, acrolein, crotonal-dehyde, benzaldehyde, and 2-furaldehyde.
10. A method in accordance with Claim 1 wherein the aldehyde vapors are introduced in a continuously produced gas plasma upstream in a carrier gas flow.
11. A method in accordance with Claim 1 wherein the aldehyde vapors are introduced in a continuously produced gas plasma inside a plasma processing chamber itself.
12. A method of sterilizing surfaces, comprising:
(a) placing the surface to be sterilized in a fluid-tight chamber;
(b) evacuating said chamber to a pressure equal to or greater than 0.1mm. of mercury;
(c) introducing into the evacuated chamber a gas containing at least ten milligrams per liter of at least one vaporized aldehyde selected from the group consisting of aromatic, heterocyclic and saturated and unsaturated acyclic aldehydes per liter of gas plasma;
(d) establishing an electromagnetic field in the 1 to 10, 000 MHz range with an average spatial density of energy of at least 0.001 watts per cubic centimeter of chamber;
(e) maintaining the abovementioned electromagnetic field for a time long enough to completely destroy all living microorganisms while not affecting the physical or chemical properties of the object to be decontaminated.
13. A method in accordance with Claim 1 wherein said gas plasma will also contain in an amount equal to or greater than ten milligrams per liter of said gas plasma of at least one vaporized biocidal agent selected from the group consisting of phenols, halogens, inorganic and organic metallic salts, organosulfur and nitrogen compounds.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA342,074A CA1104322A (en) | 1979-12-17 | 1979-12-17 | Seeded gas plasma sterilization method |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA342,074A CA1104322A (en) | 1979-12-17 | 1979-12-17 | Seeded gas plasma sterilization method |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1104322A true CA1104322A (en) | 1981-07-07 |
Family
ID=4115847
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA342,074A Expired CA1104322A (en) | 1979-12-17 | 1979-12-17 | Seeded gas plasma sterilization method |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1104322A (en) |
-
1979
- 1979-12-17 CA CA342,074A patent/CA1104322A/en not_active Expired
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