WO1996022794A1 - Method and system for sterilizing medical instruments - Google Patents
Method and system for sterilizing medical instruments Download PDFInfo
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- WO1996022794A1 WO1996022794A1 PCT/US1996/001006 US9601006W WO9622794A1 WO 1996022794 A1 WO1996022794 A1 WO 1996022794A1 US 9601006 W US9601006 W US 9601006W WO 9622794 A1 WO9622794 A1 WO 9622794A1
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Classifications
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- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B6/00—Heating by electric, magnetic or electromagnetic fields
- H05B6/64—Heating using microwaves
- H05B6/6408—Supports or covers specially adapted for use in microwave heating apparatus
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61L—METHODS OR APPARATUS FOR STERILISING MATERIALS OR OBJECTS IN GENERAL; DISINFECTION, STERILISATION OR DEODORISATION OF AIR; CHEMICAL ASPECTS OF BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES; MATERIALS FOR BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES
- A61L2/00—Methods or apparatus for disinfecting or sterilising materials or objects other than foodstuffs or contact lenses; Accessories therefor
- A61L2/02—Methods or apparatus for disinfecting or sterilising materials or objects other than foodstuffs or contact lenses; Accessories therefor using physical phenomena
- A61L2/08—Radiation
- A61L2/12—Microwaves
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61L—METHODS OR APPARATUS FOR STERILISING MATERIALS OR OBJECTS IN GENERAL; DISINFECTION, STERILISATION OR DEODORISATION OF AIR; CHEMICAL ASPECTS OF BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES; MATERIALS FOR BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES
- A61L2/00—Methods or apparatus for disinfecting or sterilising materials or objects other than foodstuffs or contact lenses; Accessories therefor
- A61L2/26—Accessories or devices or components used for biocidal treatment
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B6/00—Heating by electric, magnetic or electromagnetic fields
- H05B6/64—Heating using microwaves
- H05B6/647—Aspects related to microwave heating combined with other heating techniques
- H05B6/6491—Aspects related to microwave heating combined with other heating techniques combined with the use of susceptors
- H05B6/6494—Aspects related to microwave heating combined with other heating techniques combined with the use of susceptors for cooking
Definitions
- This invention relates to a method and system for sterilizing a metallic surgical instrument with microwave radiation and preventing arcing of the metallic surgical instrument.
- a second method of sterilization is to apply heat to the instruments.
- This method has the drawback that temperatures of about 160°C are required while heat generators to rapidly produce such temperatures are not commonly available.
- the method has further disadvantages in that the rubber and plastic washers and -bushings within the dental handpieces could potentially be damaged and long exposure times (approximately 1 hour) are needed. Gas sterilization with an ethylene oxide mixture is acceptable for both handpieces and burs. However, this is impractical because of cost of equipment, long sterilization and aeration times involved, and cost of providing adequate protection for personnel.
- Alkaline glutaraldehyde (2%) will sterilize equipment, but it must be used for 10 hours to kill spore-forming organisms or tuberculosis microorganisms and is irritating to tissue. It must also be constantly monitored as it is not effective when it is more than 2 weeks old.
- Microwave energy has been thought of numerous times in the past as a means of sterilizing materials including food products.
- microwaves are used directly and indirectly to sterilize metallic tools and instruments, which are commonly used in the medical and dental professions, several problems are immediately apparent.
- the fact that the tools are metallic means they will be heated only slightly or not at all by the microwaves, unless they happen to be magnetic which is not common. This means an auxiliary heat source is required and that must be capable of direct interaction with the microwaves in order to produce heat which will, in turn, heat the tools and, thereby, sterilize them.
- a second major problem which is common with any attempt to sterilize metallic tools or instruments is the production of arcs or corona discharge. This may occur between two tools in close proximity to each other or at the sharp edges, points or tips of a single instrument. Such an arc will actually melt the metal and destroy the usefulness of the tool.
- dental instruments are directly exposed to microwaves within a microwave oven.
- the instruments may be placed in plastic autoclave bags when exposed.
- This technique suffers from several shortcom ⁇ ings, such as (1) needing to rotate the objects in a three-dimensional manner within the oven to uniformly heat the instrument; (2) needing to shield the oven from energy not absorbed by the instruments that is reflected back to the oven; and (3) requiring either an absorber of microwaves, such as water, or an absorber of radar waves within the oven to prevent arcing.
- microwave susceptors which can be formed into flexible or rigid pouches or boxes. These are generally made by thin film deposition of metals such as aluminum or steel upon plastic films such as polyester. This, in turn, is usually bonded to paper or paperboard to provide support when heated with microwaves.
- Such films when exposed to microwaves may rapidly reach temperatures of 200°C which would be useful for sterilization, however, they have a severe drawback for the application described— namely that they do not prevent arcing of metal objects.
- the reason is that they are largely transparent to the microwave energy and, thus, some microwaves will be received by a metal object.
- microwaves reflect off metals, they actually penetrate the metal surface by about l ⁇ m. This slight penetration causes an activation of the surface electrons in a random manner and creates a current moving along the surface. If a potential charge builds up on a material to the level where it exceeds the ability of the air to carry away the charge, an arc will occur. It is well known that the build up of charge is particularly prevalent at sharp edges or points of the metal surface.
- the inventors have addressed the problem of arcing in microwave susceptor containers by inventing a container structure that allows for sterilization of metallic objects while preventing arcing.
- the container structure is disclosed in U.S. Patent Application Serial No. 08/319,944, filed October 7, 1994.
- the present invention concerns a method of sterilizing an object having the steps of providing a container with an exterior surface that has a microwave interactive layer and defines an interior space having an initial temperature. An object is then placed within the interior space of the container. Next, the microwave interactive layer is exposed to a first amount of microwaves so that the layer produces heat which raises the temperature within the interior space to a predetermined sterilization temperature. The predetermined sterilization temperature is then maintained within the interior space for an amount of time sufficient to sterilize the object.
- Another aspect of the present invention concerns a system for sterilizing an object which has a microwave source that emits microwave radiation.
- a container is positioned so as to be exposed to the emitted microwave radiation.
- the container has an exterior surface having a microwave interactive layer and defines an interior space having an initial temperature.
- the interior space of the container has an object located therein.
- a microwave source controller controls the amount of microwaves that expose the microwave interactive layer so that the layer produces heat which raises the temperature within the interior space to a predetermined sterilization temperature which is maintained thereat for an amount of time sufficient to sterilize the object.
- Each aspect of the present invention provides many advantages such as allowing one to inexpensively and quickly sterilize one or more metallic and non- metallic dental and/or surgical instruments.
- Each aspect of the present invention allows one to safely place a metallic object within a microwave source or oven without producing arcing problems.
- Each aspect of the present invention allows one to use commercially available microwave susceptor containers to sterilize metallic instruments without fear of arcing.
- FIG. 1 schematically shows a system for sterilizing an object with microwave radiation according to the present invention
- FIG. 2 shows both a sterilization bag and cassette containing a surgical instrument that are placed in a microwave device for sterilization according to the present invention
- FIG. 3 shows a perspective, cut-away view of a first embodiment of a sterilization container according to the present invention
- FIG. 4 shows a top view of the sterilization container of FIG. 3
- FIG. 5 shows a top perspective view of a tray to be used with the sterilization containers of FIGS. 3, 4, and 6-1 1;
- FIG. 6 shows a top view of a second embodiment of a sterilization container according to the present invention.
- FIG. 7 shows a top view of a first embodiment of a sterilization container with a viewing window according to the present invention
- FIG. 8 shows a top view of a second embodiment of a sterilization container with a viewing window according to the present invention
- FIGS. 9a-d show a third embodiment of a sterilization container with a viewing window according to the present invention.
- FIGS. lOa-b show a fourth embodiment of a sterilization container with a viewing window according to the present invention
- FIG. 11 shows a top view of the embodiment of a sterilization container of FIG. 3 with a visual indicator
- FIG. 12 shows an embodiment of the layered structure of the exterior surface of the sterilization container of FIG. 3;
- FIG. 13 shows a sterilization container in the form of a cassette according to the present invention
- FIG. 14 shows an exterior sensor system to be used with the sterilization containers of FIGS. 3-13;
- FIG. 15 shows an interior sensor system to be used with the sterilization containers of FIGS. 3-13;
- FIG. 16 shows an embodiment of a hermetic valve to be used with the interior sensor system of FIG. 15;
- FIG. 17a shows a plot of the temperature within the interior of the sterilization containers of FIGS. 3-13 versus time when the power is applied in a non-pulse-like fashion according to the present invention
- FIG. 17b shows a plot of the power versus time to generate the temperature plot of FIG. 17a when the temperature within the oven is initially at ambient temperature;
- FIG. 18a shows a plot of the temperature within the interior of the sterilization containers of FIGS. 3-13 versus time when the power is pulsed on and off at full power according to the present invention
- FIG. 18b shows a plot of the power versus time to generate the temperature plot of FIG. 18a
- FIG. 19a shows a plot of the temperature within the interior of the sterilization containers of FIGS. 3-13 versus time when the power is pulsed on and off at reduced power according to the present invention
- FIG. 19b shows a plot of the power versus time to generate the temperature plot of FIG. 18a
- FIG. 20 shows a plot of the temperature within the interior of a sterilization container versus time when the temperature within the oven is at ambient temperature according to the present invention
- FIG. 21 shows a plot of the temperature within the interior of a sterilization container versus time when the temperature within the oven is below the predeter ⁇ mined sterilization temperature according to the present invention
- FIG. 22a shows a plot of the temperature within the interior of a sterilization container versus time when the temperature within the oven is at the predetermined sterilization temperature according to the present invention
- FIG. 22b shows a plot of the power versus time to generate the temperature plot of FIG. 22a when the power is applied in a non-pulse-like fashion according to the present invention.
- FIG. 22c shows a plot of the power versus time to generate the temperature plot of FIG. 22a when the power is pulsed on and off at reduced power according to the present invention.
- FIG. 1 schematically shows a system for sterilizing an object.
- the sterilization system 2 includes a microwave source 4 which emits microwave radiation 6 towards a sterilization container 8 which contains an object 10.
- microwaves are considered to be electromagnetic radiation having a frequency ranging from approximately 10 6 Hz to approximately 3 x 10" Hz. It is preferred that the frequency of the microwaves is approximately 2.450 MHz. the frequency of most commercial microwave ovens.
- microwave source 4 preferably is a microwave oven 12 which has a microwave source controller 14 which controls the amount of microwaves that are emitted by the oven 12 by controlling the power supplied to the oven 12.
- a sterilization container 8 is placed within the oven 12.
- container 8 has an exterior surface 16 which defines an interior space 18 into which the object 10 is placed.
- Container 8 preferably consists of a continuous surface having an inner surface defining interior space 18 into which the object 10 is placed.
- the continuous surface preferably has a bottom 20.
- the bottom 20 may be made of (1) a single material, such as a flexible aluminum foil or polyester, or (2) a dual layer structure with an exterior surface 22 and a support surface 24.
- Container 8 also has a top 26 attached to bottom 20. Top 26 may also have a dual layer structure like bottom 20 with or without a viewing window or patch.
- Object 10 may be any material that needs to be sterilized.
- the object 10 may be entirely or partially metallic, such as a dental instrument or a medical instrument as shown in FIGS. 3 and 5.
- the instruments are preferably placed in one of the channels of tray 28 that is positioned on support surface 24.
- tray 28 is rectangular in shape, is made of paper or plastic and has one or more rectangular or round channels or compartments 30 in which a single instrument is placed therein.
- the container 8 is hermetically sealed so that the object 10 will be in a dry environment when sterilized by oven 12. Hermetic sealing is accomplished by heat sealing the container 8 or using other suitable methods such as adhesive or tape. Hermetically sealing the object 10 within the container 8 ensures that the environment is not contaminated by viruses or the like within the volume of space. Furthermore, object 10 preferably is exposed to a dry environment within the sealed interior space 18 of container 8.
- Sterilization of object 10 by the microwaves 6 emitted by oven 12 is accomplished by having container 8 convert the microwaves that impinge on its exterior surface 16 into heat. This heat is generated within the interior space 18 in an amount that is sufficient to sterilize the object 10.
- substantially all of the exterior surface 16 of container 8 has a microwave interactive layer 32 which quickly converts some of the microwaves into heat.
- bottom 26 may also have a microwave interactive layer 32 to convert the microwaves into heat.
- An example of such a microwave interactive material is a microwave susceptor material which is well known and typically comprises a thin plastic layer with a plurality of metal (such as aluminum) conductive islands vacuum deposited therein.
- susceptor materials examples include those known by the names of (1) Accu* Crisp made by A.D. Tech of Tauton, Massachusetts; and (2) Microcrisp by James River Corp. of Mentor, Ohio.
- the susceptor material may be either flexible or rigid, such as paperboard, so that the container 8 can be formed as either a pouch or cassette, respectively.
- Such conventional microwave ovens consist of a power supply, a magnetron, a launcher, a cavity with access door and a control panel.
- the magnetron tube usually operates at 100 - 120 volts and draws 10 to 15 amperes, and generates 400 to 1000 watts of microwave power which is launched into the cavity to heat objects therein.
- Many of these conventional ovens have a form of power output control which is able to reduce the average power into the cavity.
- a duty cycle or time base is defined to be the amount of time from beginning the pulsing of power to the time pulsing is completed. So, for example, in an 800 watt oven, it is possible to achieve an average output of 400 watts, or 50% power, by pulsing the full 800 watts on and off (assuming the pulse width is equal to half the pulse period). Since these time bases are long, typically 20 seconds or more, that means that the full 800 watts would be on for 10 or more seconds and cause the arcing problems described above.
- the present invention recognizes that low microwave power needs to be generated throughout the heating/sterilizing cycle.
- the level of low microwave power needed ranges from about 1 Watt to about 400 Watts, preferably about 50 Watts to about 250 Watts.
- low wattage power output devices such as solid state transistors which can produce microwave power at ISM (Industrial, Scientific and Medical) frequencies such as 915 MHz.
- ISM Industrial, Scientific and Medical
- Another way is to use a standard microwave oven magnetron and modify the power supply so the magnetron is made to pulse on and off but does so at a very short time base - one second or preferably significantly less than one second so as to prevent the buildup of the electric field. To do this a separate filament transformer would be required.
- Another technique involves including a separate filament transformer in the power supply which can be used to control the anode plate current.
- Sterilization is accomplished by first exposing the microwave interactive layer 32 to a first amount of microwaves so that the layer 32 quickly produces heat which raises the initial temperature, T 0 , within the interior space to a predetermined sterilization temperature, T s , which ranges from about 175°C to about 200°C.
- the predetermined sterilization temperature preferably is reached from about 30 to 60 seconds after the oven 12 is initially turned on.
- the power of oven 12 is controlled so that the temperature within the interior space 18 is maintained at the predetermined temperature for an amount of time sufficient to sterilize the object 10.
- the object is exposed to the predetermined temperature for a time ranging from about 5 to 7 minutes. Examples of the temperature within the interior space 18 as a function of time are shown in FIGS. 17a, 18a, 19a, 20, 21 and 22a.
- the temperature curves of FIGs. 17a, 18a, 19a, 20, 21 and 22a are generated by controlling the power of oven 12 over time. As seen in FIG. 17a, there are two distinct regions for the temperature curve: Region I illustrates the initial exposure or power-up stage of the sterilization process and Region II illustrates the maintenance stage where the power is regulated so the temperature approaches a constant value.
- the temperature is raised in a linear manner from T 0 to T s . This can be accomplished by running the microwave oven 12 at full power, such as 150 or 200 Watts, until T s is reached.
- This initial stage is graphically shown in FIGS. 17b, 18b and 21b. It is understood that there are other ways to power up the oven 12 so that the interior space quickly reaches the sterilization temperature, T s , such as pulsing the power.
- temperature sensor 34 To monitor when the sterilization temperature is reached a temperature sensor 34 is employed.
- temperature sensor 34 consists of an infrared temperature monitor 36 mounted to an interior wall of oven 12 as seen in FIG. 14. Temperature monitor 36 is electrically connected to microwave source controller 14. Temperature monitor 36 monitors the infrared energy emitted by the surface of container 8 or of an instrument 10 through a visual window or patch of container 10 and produces a signal representative of the temperature within the interior space 18 of the container 8. The signal is then relayed to microwave source controller 14 where the power of the oven 12 is controlled so that the temperature remains essentially constant within the interior space 18 of the container 8.
- the temperature sensor 34 may be placed within the interior space 18 of container 8.
- An example of an interior sensor would be either a fiber-optic or fluoroptic temperature probe 38 electrically connected to microwave source controller 14, as seen in FIG. 15. Since probe 38 would actually be within the container, this embodiment requires that the container 8 be sealed immediately follow ⁇ ing removal of the temperature probe after sterilization of the object is complete.
- a simple hermetic valve 40 through which the probe 38 may be inserted and withdrawn, which will maintain sterility.
- the valve 40 preferably has an annular opening 42 and a tapered end 44 made of silicon rubber or other flexible elastic material.
- the tapered end 44 is inserted into a slit made in the top 26 of the container 8 and then a probe 38 is inserted into the valve 40 and placed into the interior space 18 of container 18. Once the valve 40 and probe 38 are withdrawn from the interior space 18, the slit closes so that the container 10 remains hermetically sealed.
- the temperature sensor 34 sends a signal to the microwave source controller 14 which controls the power of the oven 12 and, thus, the amount of microwaves emitted to and absorbed by the container 8.
- the microwave source controller 14 controls the power of the oven 12 and, thus, the amount of microwaves emitted to and absorbed by the container 8.
- T s the prede ⁇ termined sterilization temperature
- controller 14 reduces the power of the microwave oven 12 to approximately 100 Watts so as to maintain the predetermined temperature within the container 8.
- the power is again reduced to about 75 Watts so that the temperature will fall back towards and below T s .
- FIGS. 18 and 19 Another way to control the temperature is shown in FIGS. 18 and 19 where the power is pulsed in region II so as to maintain the predetermined sterilization tempera ⁇ ture.
- the parameters of the pulsed power are controlled in response to the temperature sensed within the container 8 by sensors 34 placed either within or outside the container 8.
- the pulse period, pulse width, the frequency of the microwave radiation or all three in combination can be varied to maintain the temperature within the container 8.
- the period of the pulsed power ranges from about l/30th of a second to about 20 seconds, preferably 1 to 5 seconds; the pulse width of the pulsed power ranges from about l/60th of a second to about 10 seconds, preferably 0.5 seconds to 2.5 seconds; and the frequency of the pulses ranges from about 1 MHz to about 10 GHz, preferably 100 MHz to 6 GHz.
- FIGS. 18 a and b show a method of pulsing where the power is alternatively pulsed on at full power, such as 200 Watts, and then off.
- full power such as 200 Watts
- the pulses are generated at a power which is significantly less than the oven 12 can generate at full power.
- the pulses are triggered on and off in a manner similar to that described above with respect to the method of FIGS. 18a and b.
- oven 12 is set at full power of 200 Watts and the pulses will be generated at a power ranging from about 50 Watts to about 100 Watts.
- the pulses in the method of FIG. 19 have a greater width, approximately 2 times, than the pulses generated in the method of FIG. 18. This leads to the temperature within container 8 reaching equilibrium near T s more quickly than in the method of FIG. 18. Equilibrium is reached more quickly because the swings in temperature about T s are not as great which leads to needing less microwave power for each pulse. This reduction in pulse power allows for greater control of the microwave radiation emitted by the oven 12.
- a pouch was made from a sample of a flexible susceptor obtained from James River Corporation (Milltown, Ohio). The pouch was approximately 6 inches long and 3 inches wide and the seams were sealed with masking tape. A single dental explorer was placed in the pouch or container and the pouch was sealed with masking tape. The pouch was then placed in a Hirst MicroAire microwave oven manufactured in England and having a power supply which allows the operator to vary the power smoothly from 25 to 2000 watts. In this test the oven was first set at a frequency of 2,450 MHz and a power output of 800 watts as measured into a 1000 ml water load. The oven was energized and there was brilliant flash and the pouch began to burn. The fire was extinguished and the explorer removed from the pouch - the tip was completely melted into a ball and the instrument scorched.
- a second pouch or container was prepared with a new dental- explorer following the steps outlined above. However, this time the power of the Hirst oven was adjusted downwardly to 150 watts. Now when the oven was energized there was no flash or fire and the susceptor became hot. The microwave oven was shut off after 60 seconds and the pouch removed from the oven and the explorer was examined and it was in perfect condition. EXAMPLE 2;
- Example 2 Following the procedures described in Example 1, a dental explorer and a hand tool used for dental drilling were placed in a susceptor pouch along with spore strip biological indicators which were placed into the hand tool end or taped to the tools. The tools were placed in extremely close proximity. A small slit was made in the pouch and a fiber-optic temperature probe inserted into the pouch. The Hirst microwave oven was set at 2,450 MHz and energized at 150 watts output. The temperature inside the pouch was monitored on a model 750 Luxtron Fluoroptic Thermometer.
- the temperature rapidly reached 375°F (191 °C) and then the power was shut off manually and restarted within a few seconds in order to maintain the temperature within the pouch in the range of 350° to 375°F (177° to 191°C). This was repeated for 7 minutes, effectively cycling the temperature in the range desired.
- the pouch and its contents were removed from the oven, the temperature probe removed from the pouch and the slit sealed with masking tape.
- the pouch was sent to a qualified microbiology laboratory which analyzed the spore strips and reported that a 6 log sterility had been achieved. No arcing or damage to the metallic tools occurred as well.
- microwave oven 12 Besides exposing the container 8 solely to microwave radiation, it is possible to simultaneously expose the container 8 and the object 10 within microwave oven 12 to both microwave energy and hot air. This heating combination has several advantages over using microwaves alone:
- T s the temperature inside the container 8 and its contents it is easier to maintain the temperature inside the container near the predetermined sterilization temperature, T s .
- T s the sterilization temperature
- T s the sterilization temperature
- little or no microwave energy may be required once the initial heating to the sterilization temperature has been accomplished.
- the air within oven 12 is at a temperature slightly below the sterilization temperature, such as 325°F (163°C)
- the sterilization temperature is achieved within container 8 it can be maintained with low levels of microwave energy, either continuous or pulsed.
- the swings of temperature above and below the desired sterilization temperature will be narrowed as will be seen in the illustrations and examples below.
- hot air/microwaves Another advantage of hot air/microwaves is that it facilitates the sterilization of large medical instruments. Since the actual heat produced by the susceptor, which is of a very low thermal mass, would ordinarily be too small to heat a large mass of instruments alone, adding hot air would supplement the microwave generated heat and aid in the sterilization of large instruments which need to be subjected to larger heat quantities for sterilization to occur.
- a flexible rectangular pouch or container with dimensions of 6"x3" was pre ⁇ pared from an aluminum microwave susceptor.
- a dental explorer inoculated with spore forming bacteria was placed therein and the pouch was sealed with masking tape.
- a Luxtron temperature probe was placed inside the pouch, through a small slit made in the pouch.
- the pouch was placed in a Hirst MicroAire oven which had been adjusted to a microwave power output of 175 watts at 2,450 MHz.
- the air in the oven was at the ambient temperature of 70°F (21°C).
- the oven was energized and the temperature monitored.
- the temperature inside the pouch reached 350°F (177°C) in approximately 35 seconds.
- the power was then pulsed on and off at full power to maintain an average temperature of 375°F (191°C).
- Example 2 the test described in Example 2 was repeated, howev ⁇ er, the oven 12 was first preheated to the predetermined sterilization temperature of 375°F (191°C).
- the microwave oven 12 was energized as before and the container ' s internal temperature reached 350°F (177°C) in about 25 seconds.
- the microwave oven 12 was shut off and then pulsed on and off at a reduced power of approximately 85 Watts for about one minute until a stable internal temperature of 375°F (191 °C) was maintained. After 7 minutes the oven 12 was shut off and the sample removed.
- a 6 Log reduction of microorganisms was achieved. Again no arcing or damage to the tools occurred. Note that the triggering of the pulses of Examples 1-3 was essentially the same as the triggering described for the methods shown in FIGS. 18- 19.
- container 8 which is totally made of a susceptor material
- other structures for container 8 are possible.
- the central portion of the container 8 is made of a microwave interactive layer 32 while the end portions 41 are made of a foil or a foil laminated to paper or paperboard in order to prevent puncture of the surface of the container and to prevent the formation of a hot spot due to the proximity of a point of a sharp metal object 8 to the layer 32.
- FIGS. 7-10 it is also possible to design a container in which the object 10 which is sterilized can be seen in the visual or infrared spectrum without opening the container 8. It would be an advantage to have an optically transparent window in the container in order that the dental or medical technician be able to see the instruments contained therein. Another reason is that, if the window material is chosen to be transparent to infrared, then an infrared sensor could monitor the surface temperature of the instruments or another object inside the container without invading the hermetic seal.
- a susceptor container has a central see-through patch 42 made of a foil with a plurality of holes 44 of such dimensions to act as waveguide-beyond-cutoff and thereby permit the transmission of light out of the container 8 without the transmission of microwave power therethrough as well.
- the central see-through patch 42 may be made of a clear plastic film such as polyester, capable of withstanding the heat of contact with the susceptor, or otherwise thermally insulated from the susceptor. Such a window would be allowed providing that the microwave oven power was kept low enough to prevent arcing.
- the second embodiment pertains to a container having two surfaces, each with an exterior surface and an inner surface. Both inner surfaces face each other and define a volume of space into which the metal object is placed.
- One or more of the surfaces is made of a microwave interactive layer, like a susceptor material, that absorbs microwave radiation impinging on an exterior surface of the container and converts the absorbed microwave radiation to radiant heat energy.
- one or more of the surfaces has an optically transparent material capable of withstanding temperatures of at least 400°F (204°C). Two examples of the second embodiment of the see-through patch 42 are given below. EXAMPLE 1;
- a rectangular sheet of susceptor material 46 having dimensions of approximately 6"x9" is cut and has a rectangular heat zone border 48.
- the susceptor material 46 preferably is made of an aluminized polyester film or a steel coated polyester film bonded with adhesive to paper or paperboard.
- a similarly sized sheet of aluminized polyester film 50 is provided with a rectangular heat zone border 52 as seen in FIG. 9b.
- the aluminized polyester or steel coated film 50 is placed over susceptor material 46 where the heat zone borders 48 and 52 are bonded together with a heat sealer in order to make a pouch or container 8, as seen in FIG. 9c.
- Each heat zone border 48 is preferably free of the aluminum or steel coating of the susceptor 46 and is made of polyester, paper or paper coated with adhesive so that burning at the interfaces during sterilization.
- the cross-sectional view of the pouch 8 as seen in FIG. 9d shows that the top of the pouch with the aluminized or steel coated polyester film 50 is optically transparent while the bottom of the pouch that has the susceptor is opti ⁇ cally opaque.
- Film 50 preferably is made of a polyester layer 54 having a thickness of approximately 1 mil which is joined to an interior aluminum layer 56 which has a thickness of approximately 150 nanometers.
- the opaque bottom preferably includes an interior aluminum layer 58 having a thickness of approximately 150 nanometers located on top of a polyester film 60 having a thickness of approximately 1 mil.
- the polyester film 60 is adhered via adhesive 62 to a paper outer layer 64 having a thickness of approximately 5 mils.
- Adhesive 62 is well known in the art and has a thickness of approximately 0.1 mils.
- the pouch 8 was then placed in a laboratory microwave oven manufactured by Precision Scientific after first having heat sealed a dental explorer therein.
- the oven was set at a frequency of 2,450 MHz at a power of 240 watts so that the pouch 8 reached a temperature of 370°F (188°C) as monitored using a Luxtron temperature probe inside the pouch 8.
- the heating was continued for 7 more minutes while pulsing the power on and off to maintain an average temperature of 360°F (182°C).
- the window was intact as was the rest of the pouch 8.
- a rectangular pouch 8 having dimensions of 6"x9" is formed from a single sheet of susceptor material 46 that is folded to give a top 26 and a bottom 20 as shown in FIGS. lOa-b.
- a rectangular section 66 having dimensions of about 1 l/2"x4" is cut out of the center of the top 26 to form an opening.
- a rectangle of plain polyester film 68 having dimensions of about 2"x5" is placed inside the pouch 8 and is positioned to cover the opening. The film 68 is then bonded to the top 26 by a heat sealer.
- a metallic dental explorer was heat sealed within the pouch and the entire pouch heated in the Precision Scientific oven set at 2,450 MHz at a power of 240 watts for 7 minutes. Once 350°F (177°C) was reached the power was pulsed on and off to maintain an average temperature of 360°F (182°C). After removal -from the oven, the pouch 8 was examined and there were no signs of damage to the window or the susceptor, or the dental explorer due to arcing. This reveals that windows can be made of different sizes to represent part of one or both sides, or an entire side of a pouch or rigid container 8.
- Materials for the window can range from polyester to nylon films to other thin film optically transparent materials capable of withstanding temperatures of at least 400°F.
- the film may be coated with aluminum, steel or other material normally used to produce a susceptor, but without the paper backing. In this case, the film, when edge-bonded to the bottom susceptor will not only be structurally stable but will also heat, thereby aiding in the heating of the pouch.
- FIG. 1 1 Another feature of the container 8 which would be desirable is a visual indicator 70 as seen in FIG. 1 1 which illustrates when sterility has been achieved.
- This may be achieved with temperature sensitive inks or chemicals, commonly known in the industry, which integrate temperature and time, to provide a permanent marking or visual indicator of sterility.
- a visual indi ⁇ cator such as a color or the alpha-numeric indicia "STERILIZED” or "STERILIZA ⁇ TION,” appear indicating that the object has received a sufficient of heat to be sterilized.
- Another desirable feature of the container 8 is to insulate the outer surfaces so as to retain the heat created within the container. This can be done, for example, by placing an insulator layer 72 on a portion of or on the entire exterior surface 16 of container 8 as seen in FIG. 12. Insulator layer 72 may be made of a foam coating or a fibrous layer.
- the container 8 may be a permanent or semi-permanent structure than disposable.
- a structure which may be constructed of a high heat plastic, for example, has a rigid microwave interactive layer 32 on its inner surface.
- the entire container would have a base and a cover which might be attached by a hinge on one side and provided with a lockdown or other sealing mechanism to maintain a hermetic seal during and after the heating cycle.
- the cover and base Once closed and hermetically sealed, the cover and base define an interior space that contains one or more metallic surgical instruments 10. It may be necessary to provide a self-sealing valve to release pressure during heating.
- the con ⁇ tainer with tools therein is heated in the special low power microwave oven and, having reached sterility, is removed from the oven and maintained in a sealed fashion until the tools are needed by the dentist, doctor or other professional.
- a con ⁇ tainer may also be provided with a sterility indicator and temperature sensor.
- container 8 may be used for other purposes, such as (1) containing and treating metallic materials with microwave radiation and (2) containing and cooking food items within a metallic vessel, like a pot or pan.
Abstract
Description
Claims
Priority Applications (4)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
CA002216650A CA2216650C (en) | 1995-01-26 | 1996-01-23 | Method and system for sterilizing medical instruments |
JP8523007A JPH11505436A (en) | 1995-01-26 | 1996-01-23 | Method and apparatus for sterilizing medical instruments |
AU47676/96A AU4767696A (en) | 1995-01-26 | 1996-01-23 | Method and system for sterilizing medical instruments |
DE19681227T DE19681227T1 (en) | 1995-01-26 | 1996-01-23 | Method and system for sterilizing medical instruments |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US08/381,685 | 1995-01-26 | ||
US08/381,685 US5552112A (en) | 1995-01-26 | 1995-01-26 | Method and system for sterilizing medical instruments |
Publications (1)
Publication Number | Publication Date |
---|---|
WO1996022794A1 true WO1996022794A1 (en) | 1996-08-01 |
Family
ID=23505980
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
PCT/US1996/001006 WO1996022794A1 (en) | 1995-01-26 | 1996-01-23 | Method and system for sterilizing medical instruments |
Country Status (7)
Country | Link |
---|---|
US (2) | US5552112A (en) |
JP (1) | JPH11505436A (en) |
AU (1) | AU4767696A (en) |
CA (1) | CA2216650C (en) |
DE (1) | DE19681227T1 (en) |
TW (2) | TW394690B (en) |
WO (1) | WO1996022794A1 (en) |
Cited By (1)
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---|---|---|---|---|
EP0990372A1 (en) * | 1997-06-11 | 2000-04-05 | Amcor Packaging (Australia) Pty, Ltd | Preferential heating of materials by use of non-ionising electromagnetic radiation |
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Also Published As
Publication number | Publication date |
---|---|
CA2216650A1 (en) | 1996-08-01 |
AU4767696A (en) | 1996-08-14 |
TW394690B (en) | 2000-06-21 |
US5552112A (en) | 1996-09-03 |
TW510802B (en) | 2002-11-21 |
US5811769A (en) | 1998-09-22 |
CA2216650C (en) | 2001-04-03 |
JPH11505436A (en) | 1999-05-21 |
DE19681227T1 (en) | 1998-01-08 |
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