Abstract:
A free radical decontamination method and system. The system is comprised of a chamber defining a region, and a generator for generating free radical reach effluent from a free radical electric generator and hydrogen peroxide solution with water. A closed loop circulating system is provided for supplying the mixture of free radicals from the electric generator mixed with the hydrogen peroxide solution in the form of the effluent to the chamber.

Description:
ACKNOWLEDGMENT OF GOVERNMENT SUPPORT 
       [0001]    This invention was made with Government support under Grant No. 0750056, awarded by the National Science Foundation, R44DE017831-03 awarded by NIH. The government has certain rights in the invention. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates generally to the art of sterilization and decontamination, and more particularly to a system for sterilization of heat sensitive devices. The present invention also relates to a gaseous sterilization process carried out at atmospheric pressure. 
         [0004]    2. Description of Related Art 
         [0005]    Sterilization methods are used in a broad range of applications, and have used an equally broad range of sterilization agents. As used herein the term “sterilization” refers to the inactivation of bio-contamination, especially on inanimate objects. The term “disinfection” refers to the inactivation of organisms considered pathogenic. 
         [0006]    It is known that pulsed or silent electric discharge in air or other gases produces non-thermal plasma. Non-thermal plasma processing involves producing plasma in which the majority of the electrical energy goes into the excitation of electrons. These plasmas are characterized by electrons with kinetic energies much higher than those of the ions or molecules. The electrons in these plasmas are short-lived under atmospheric pressure; instead they undergo collisions with the preponderant gas molecules. The electron impact on gas molecules causes dissociation and ionization of these molecules, which creates a mix of reactive species, in the form of free radicals, ions and secondary electrons. These reactive species cause unique and diverse chemical reactions to occur, even at relatively low temperatures. These chemical reactions are utilized in low temperature decontamination and sterilization technologies. 
         [0007]    It is also known to use vaporized hydrogen peroxide (VHP) for sterilization. Known methods of sterilization with VHP include open loop systems, in which the VHP is applied to the items to be sterilized and then exhausted, and closed loop systems, where sterilizing vapors are recirculated. 
         [0008]    In a known closed loop system, a carrier gas, such as air, is dried and heated prior to flowing past a vaporizer. A hydrogen peroxide aqueous solution is introduced into the vaporizer and vaporized. The resulting vapor is then combined with the carrier gas and introduced into a sterilization chamber. A blower exhausts the carrier gas from the sterilization chamber and recirculates the carrier gas to the vaporizer where additional VHP is added. Between the sterilization chamber and the vaporizer, the recirculating carrier gas passes through a catalytic destroyer (where any remaining VHP is eliminated from the carrier gas), a drier, a filter and a heater. 
         [0009]    United States Patent Application Publication No: US 2005/0129571 A1 by Centanni discloses a closed loop sterilization system. The purpose of using the closed loop is the increase of the free radical concentration in the circulating effluent. Centanni teaches that there should be a VHP (vapor hydrogen peroxide) destroyer employed in the loop. Cetanni teaches that the ozone is mixed with the hydrogen peroxide vapor and the vapor is produced by injecting hydrogen peroxide water solution on a hot plate and thus evaporating it. 
       SUMMARY OF THE INVENTION 
       [0010]    The present invention provides a method and system for sterilization. Free radicals are generated using a plasma electric discharge generator and passed through a hydrogen peroxide vaporizer to produce highly bactericidal gaseous effluent. The effluent passes through a chamber, and then is recirculated—a portion is routed through the generator, and the generator output is added to the rest of the recirculated effluent to pass back through the vaporizer and again into the chamber, in a closed loop system. The chamber can be in the form of a tumbler to sterilize items like surgical masks or fabrics or medical waste, or in the form of a stationary chamber for more solid items. A blower may be provided inside the chamber to create turbulence. 
         [0011]    For use in pre-heating and drying the items to be sterilized, an input conduit equipped with a valve, heater and filter supplies fresh air to the system and an exhaust blower with an upstream filter and a free radical neutralizer removes moisture and active radicals from the system. The exhaust blower may be operated at a low speed mode during sterilization to create a negative-pressure condition in the chamber. 
         [0012]    The invention also presents a method of sterilizing items in a chamber using the above-described apparatus. The method includes placing the items in the chamber, pre-heating and drying them in an open-loop, disinfecting using a closed loop circulating system to supply bactericidal free radicals generated by an electric discharge with free radicals in antimicrobial liquid to the chamber, then flushing and drying the system in an open-loop. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0013]      FIG. 1  shows a block diagram of the invention with a tumbler-type chamber 
           [0014]      FIG. 2  shows a block diagram of another embodiment of the invention with a stationary chamber with heating 
           [0015]      FIG. 3  shows a flowchart of the method of the invention 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0016]      FIGS. 1 and 2  show block diagrams of a sterilization system, illustrating two embodiments of the present invention. Broadly stated, system utilizes a combination of broad mixture of free radicals used in sterilizing and decontamination devices to sterilize items placed in the chamber or chamber. 
       Details of the Apparatus 
       [0017]    Items to be sterilized are placed in a chamber  10 . In  FIG. 1 , the chamber  10  is shown as a tumbler-type chamber, which is rotated around a longitudinal axis  54 , for example by motor  51 , in the manner of a conventional home clothes dryer. Such a tumbler-type chamber  10  would be appropriate for fabric items  56  such as towels and cloths, surgical masks and gowns, gloves, etc. The tumbler design could also be used to sterilize shredded medical waste within the teachings of the invention. 
         [0018]      FIG. 2  illustrates an embodiment appropriate for more rigid items  62 , such as laboratory glassware, surgical implements, dental tools, etc. The items  62  may be put on shelves  60 , the shelves preferably being made of wire or perforated to allow free circulation of effluent around the items  62 . 
         [0019]    For the sterilization of instruments with internal conduits or lumens such as endoscopes or dental handpieces  67 , a portion of the sterilant gas can be forced through the instruments  67 , while the outer surfaces of the instruments  67  are sterilized by the effluent in the chamber, as discussed below. To do this, an additional conduit can be supplied with sterilant gas from the effluent input conduit  34 , shown in the figure as flexible hose  63 . The hose  63  is equipped with one or more appropriate connectors  65  to plug into the handpiece  67 . 
         [0020]    Additionally a circulating blower  28  can be used to increase effluent turbulence in the chamber. The blower  28  can be placed in the chamber  10 , as shown in  FIG. 1 , or outside, connected to the chamber by ducts, as shown in  FIG. 2 . A heater  64  can be put in the ducts to heat the air circulated by the blower  28 , or, alternatively, the chamber may be directly heated by elements  66  either in the chamber or attached to the walls of the chamber. 
         [0021]    An effluent generator  46  is used for production of effluent for sterilization or decontamination of the chamber and its contents and for powering the circulation of effluent in the closed loop, to be described later. The effluent generator  46  includes a blower with flow distributor  14 , a plasma electric free radical generator  30  and a vaporizer  14 . 
         [0022]    The blower with the flow distributor  14  takes recirculated effluent from the chamber  10  via conduit  36 , and distributes it proportionally through conduit  40 , which is coupled, optionally through a filter  50 , into the plasma generator  30 , and through conduit  38 , again through optional filter  50 , into T-junction  48 . The recirculated effluent is preferably distributed in proportions of approximately 30% to conduit  40 , and approximate 70% to conduit  38 . 
         [0023]    Thus, most of the recirculated effluent bypasses the plasma generator  30 . The lesser proportion of the effluent passes through generator  30 , picking up new free radicals, and is mixed back in the rest of the effluent at T-junction  48 . It will be understood that these percentages are for the purpose of example, and other divisions may be chosen within the teachings of the invention. 
         [0024]    Optionally, a carrier gas  53 , such as air, oxygen, nitrogen, carbon dioxide, helium, argon, or a combination of carrier gases, can be introduced into the effluent generator  46  to be mixed with the effluent in the closed system. This can be done as an additional input to blower/distributor  14 , as shown in  FIG. 2 . 
         [0025]    The plasma free radical generator  30  can be any kind of dielectric barrier discharge device. A device which can be used within the teachings of the invention is an ozone generator such as, for example, ozone generator cell SY-G20 manufactured by Longma Industrial Zone, Bao&#39;an District, Shenzhen, 518108, P.R.C. 
         [0026]    The mixture of recirculated effluent from blower/distributor  14  and recirculated effluent with additional free radicals from the plasma generator  30  mixes in T-junction  48  and enters vaporizer  32 . 
         [0027]    The vaporizer  32  contains liquid sterilizing agent such as hydrogen peroxide solution, and the mixture from the T-junction  48 , in contact with the solution, produces bactericidal effluent. While the invention is described with particular reference to hydrogen peroxide as the sterilizing agent, it will be appreciated that the system is also applicable to other solutions and pure liquids, such as peracetic acid or formalin solution. 
         [0028]    The vaporizer  32  can be in the form of a “bubbler”, in which the gas passes through a container of liquid, or the vaporizer could use plates or wicks over which the gas passes, as is known in prior-art devices. Preferably, the vaporizer  32  uses a measured amount of sterilizing agent, preferably in a pre-measured cartridge which can be inserted into the vaporizer, such that the agent is substantially or completely consumed in the course of a sterilizing run. The vaporizer can thus supply a specific small amount of hydrogen peroxide to the evaporator from a cartridge which is empted and dried during the sterilization process. The drying of the cartridge is accomplished by heating it using a small heater and a limited filtered air flow through the cartridge into the system. This way there is no danger that hydrogen peroxide liquid is present in the cartridge at the end of the cycle when a person/operator will insert a new cartridge for next cycle. 
         [0029]    The effluent produced in the vaporizer  32  is then introduced into the chamber  10 , completing the closed loop of the system. 
         [0030]    In addition to the closed loop system, an open loop system is also provided for the purpose of pre-heating and drying the chamber  10  before and after the circulation of bactericidal effluent through the closed loop system. The open loop system uses a blower  16 , exhausting to atmosphere  56 , to draw air from an air input  58  through input valve  18  and heater  26  into chamber  10 . The input air may be filtered by filter  20 , which is preferably of the high efficiency particulate air (HEPA) variety. The heated, preferably filtered, air is introduced into the chamber  10  through conduit  42 . The input of the blower  16  is connected to the chamber  10  through conduit  44  and a Free Radical Destroyer (FRD)  24 , which destroys any free radicals which might remain before the air is exhausted  56 . A second filter  22 , again preferably of the HEPA type, can be provided in conduit  44  to filter out any particles which would otherwise enter the FRD or be exhausted to the atmosphere. The presence of HEPA filters  20  and  22  at the input and exhaust ensures that there is no microorganism transfer between the ambient air and the sterilization system and vice versa. 
         [0031]    The simplest FRD is an activated carbon filter, for example, the Vent Pure “D” from General Carbon Corp. of Paterson, N.J. 
         [0032]    By opening valve  18  and turning on heater  26  and blower  16 , the chamber  10  and items  56  or  62  within, can be dried and pre-heated before the closed loop operation is begun. Once the pre-heating and drying step is completed, valve  18  is closed and heater  26  is turned off. 
         [0033]    Preferably, blower  16  is of a controllable-speed type, so that it may be operated at a reduced speed during closed-loop operation. This will induce a slight negative pressure in the chamber  10 , preventing leakage of effluent from the chamber. However, the blower could be a single-speed blower, in which case it would be turned off after the pre-heating step. 
         [0034]    After pre-heating, the system is operated in closed-loop mode by starting blower/distributor  14  and plasma generator  30 . The effluent mixture circulates continuously through the loop, from generator  46  through conduit  34 , through chamber  10  and conduit  36 , back to the generator  46 . 
         [0035]    When this cycle is finished plasma generator  30  is turned off, valve  18  is opened, and blower  16  is turned on full speed in order to remove the active free radicals from the effluent using FRD  24 , and to dry the chamber  10  and the sterilized equipment  56  or  62 . 
         [0036]    The closed loop blower/distributor  14  may remain on, if desired, so as to circulate air through the closed loop to dry the free radical source  46  and vaporizer  32 . Heater  26  may optionally be turned on at this stage, as well, so that heated air is circulated through the vaporizer in order to evaporate residual remains of liquid solution of hydrogen peroxide. Alternatively, blower/distributor  14  may be turned off if it is not desired to circulate air through the closed loop portion of the system during this drying step. 
         [0037]    A controller  12  is provided in order to control the operation of the various parts of the system. In the embodiment of  FIG. 2 , a temperature sensor  52  is provided in the chamber  10 . The controller  12  can then maintain a selected temperature in the chamber  10  by reading the temperature through sensor  52  and controlling chamber heaters  64  and/or  66  as needed. 
       Method of Operation 
       [0038]    As shown in  FIG. 3 , the sterilization process consists of three phases:
     80 —Start the method     70 —Phase I—Pre-sterilization drying and heating (Open Loop)
         81 —During this phase the exhaust blower  16  is turned on, the valve  18  is opened (if closed) and the heater  26  is turned on. This causes fresh air from the inlet  58  to flow through valve  18 , optional HEPA filter  20 , and heater  26  into chamber  10  via conduit  42 . The heated air dries and heats the sterilized items and is expelled through conduit  42  via optional filter  22 , free radical destroyer  24  and exhaust blower  16 .   
         82 —The drying and heating is continued for a sufficient time, for example approximately 5 minutes. If desired, a heat sensor or humidity sensor (not shown) could be provided at the exhaust  56  or in conduit  44 , coupled to the controller  12 , so that the duration of the pre-heating could be controlled based on empirical data rather than an arbitrary elapsed time. Optionally, if a chamber temperature sensor  52  is provided, the controller  12  may operate heater  26  and, if provided, chamber heaters  64  and/or  66  to maintain a desired pre-heat temperature in the chamber.
         83 —After the chamber and the sterilized items are dried and heated the input valve  18  is closed.     84 —The exhaust blower  16  is turned off (or reduced to minimum speed, if this ability is available)   
         71 —Phase II—Sterilization (Closed Loop)
         85 —The plasma generator  30  and the closed loop blower/distributor  14  are turned on. This causes the air to circulate in the closed loop through the free radical generator  46  and the chamber  10 , as described in the description of the apparatus, above.     86 —The closed loop system produces continuously free radical rich effluent that sterilizes items in the chamber  10 . The closed loop operation continues for a time sufficient for sterilization. As an example, a duration of approximately 20-30 minutes should be sufficient for adequate sterilization of most items. If provided, the controller  12  will activate chamber heaters  64  and/or  66  to maintain a desired temperature in chamber  10 , as measured by sensor  52 .     87 —At the end of the sterilization period, the plasma generator  30  is turned off.   
         72 —Phase III—Post-Sterilization Drying and Clearing (Open Loop)
         88 —Input valve  18  is opened, heater  26  is turned on and the exhaust blower  16  is turned on. The closed loop blower/distributor  14  may remain on during this Phase III in order to dry free radical source  46 , or, if desired, blower/distributor may be turned off in step  87 . The air flows from the input  58  via conduit  42  into the chamber  10  drying the items and, if blower  14  remains on, the free radical source  46 . The moist air is expelled into the atmosphere via filter  22  and free radical destroyer  24 .     89 —The open loop operation is maintained for a time sufficient to dry and clear the chamber  10 . A period of, for example, five minutes should suffice.     90 —Heater  26  is turned off, with blower  16  (and blower  14 , if desired) remaining on.     91 —Fresh air is passed through the system for a sufficient time to cool down to the ambient temperature. For example, a few minutes operation would suffice for cooling. Optionally, if sensor  52  is provided in the chamber, the controller  12  could be programmed to continue this cooling until a desired temperature is reached.     92 —Blower  16  is turned off, as well as blower  14  if it is still on. Valve  18  may be closed at this time, or left open for the next run.   
         93 —The method ends. The chamber  10  may now be opened and the items  56 / 62  removed. New items may be put in the chamber, if desired, and the process repeated again from  80 .   
 
         [0056]    Accordingly, it is to be understood that the embodiments of the invention herein described are merely illustrative of the application of the principles of the invention. Reference herein to details of the illustrated embodiments is not intended to limit the scope of the claims, which themselves recite those features regarded as essential to the invention. The drawings are for the purpose of illustrating embodiments of the invention only, and not for the purpose of limiting it.