US3716961A

US3716961A - In-package sterilization

Info

Publication number: US3716961A
Application number: US00102479A
Authority: US
Inventors: P Cope; J Miles
Original assignee: Procter and Gamble Co
Current assignee: Procter and Gamble Co
Priority date: 1970-12-29
Filing date: 1970-12-29
Publication date: 1973-02-20
Anticipated expiration: 1990-02-20
Also published as: GB1383013A; DE2164779A1; BE777451A; IT946256B; FR2121012A5; GB1383014A; DE2164779B2; DE2164779C3; CA953073A; NL7117794A

Abstract

A method for sterilizing articles on a production basis, within individual storing and shipping packages after the articles are packaged. One or more articles are sealed within a gas-permeable package, sterilant is injected into the package, and the package containing both the article and the sterilant is moved to a well ventilated holding area where it is held until sterilization is complete.

Description

United States Patent 1 Cope et a1.

[ 51 Feb. 20, 1973 [541 IN-PACKAGE STERILIZATION [75] Inventors: Paul E. Cope, Cincinnati; Joe G.

Miles, Grecnhills, both of Ohio [73] Assignee: The Procter & Gamble Company, Cincinnatti, Ohio [22] Filed: Dec.29, 1970 21 App1.No.: 102,479

[52] US. Cl. ..53/21 FC, 21/58, 53/22 B [51] Int. Cl. ..B65b 55/18 [58] Field of Search ..53/7, 21 FC, 112; 21/58 [56] References Cited UNITED STATES PATENTS 6/1970 Andersen et a1. ..53/1 12 5/1929 Gibson ..53/7X 5/1941 Tirrell ..53/7X Primary ExaminerTravis S. McGchcc Attorney-John V. Gorman and Richard C. Wittc [57] ABSTRACT A method for sterilizing articles on a production basis, within individual storing and shipping packages after the articles are packaged. One or more articles are sealed within a gas-permeable package, sterilant is injected into the package, and the package containing both the article and the sterilant is moved to a well ventilated holding area where it is held until sterilization is complete.

2 Claims, 4 Drawing Figures PATENTEDFEB201973 3,716,961

INVENTORS Po U! E. Cope Joe 6. Miles K ATTORNEY lN-PACKAGE STERILIZATION FIELD OF THE INVENTION DESCRIPTION OF THE PRIOR ART Most hospitals presently use traditional linen for sheets, drapes, hats, masks, towels, etc. in operating rooms and patients rooms. After use, the dirty linen is first washed, then sterilized in an autoclave, and sub-- sequently packed in an overwrap of linen or paper to maintain the linen in a sterile condition until it is used. The sterile shelf life of this combination is approximately 30 days.

Some hospitals now use packaged, presterilized disposables." The packaged disposables have a longer shelf life than the linen which hospitals sterilize themselves. Also, by using disposables, hospitals experience a cost savings because they no longer have to carry the inventory of linen, they no longer have to maintain as much washing and sterilization equipment, and they can eliminate some of the labor required to operate the eliminated equipment.

The classical way to sterilize articles is by using superheated steam as the sterilant in an autoclave which entails a batch operation in a large pressure vessel. But

' articles requiring sterilization which are heat and/or moisture sensitive are deleteriously affected by the superheated steam. Also the batch operation required in this process does not allow a smooth flow of materials through a production line, and superheated steam is not the most effective sterilant, i.e., it does not eliminate all living organisms and lengthy exposure to the superheated steam is required.

The necessity for complete sterilization of some heat and/or moisture sensitive articles used by physicians and hospitals has resulted in a search for more effective sterilants and more rapid processes. Ethylene oxide gas as a sterilant has been found to be very effective and satisfactory for the complete elimination of micro organisms and organic life. Ethylene oxide is not only exceedingly efficient, but also does not change the composition or physical characteristics of heat and/or moisture sensitive materials.

Ethylene oxide is used in a sterilization process similar to the process wherein superheated steam was the sterilant in that sterilization is done on a batch basis in a large pressure vessel. The process described in U. S. Pat. No. 2,938,766, Hall, issued on May 21, 1960 is representative of the sterilization process presently used by manufacturers of disposables. The process of the Hall patent requires seven steps after the disposable product is encapsulated within its own individual gaspermeable protective package and placed within a pressure chamber. These steps are: (l) preheat, (2) draw first vacuum, (3) introduce sterilant to chamber, (4) exposure to sterilant for up to 4 hours, (5) draw second vacuum, (6) flush with sterile air, and (7) remove the packages. That process takes up to seven hours for completion of the seven steps. The sterilant must permeate the package twice, first to get inside and second to get back out, before the package is removed from the pressure chamber.

The inherent disadvantages associated with the prior art methods are (l) the batch operation interrupts the smooth flow of a manufacturing line, causing a bottleneck, (2) admittance of the sterilant into the package by permeation of the gas into the package requires an extended time period on the production line, and (3) sterilization by this method is relatively expensive.

Another means of sterilizing articles within a package is exemplified by U. S. Pat. No. 3,476,506, Andersen et al., issued on Nov. 4, 1969, which discloses a sterilization apparatus for batch type sterilization on a relatively infrequent basis. The sterilant contained in an impermeable vial, and the article to be sterilized are both placed within a gas permeable outer package. After the outer package has been sealed, sterilization is commenced by breaking the vial and thereby exposing the article to the sterilant. The permeability of the outer package is relied on to control the sterilant concentration both inside and outside the package. This method of sterilization has inherent disadvantages in that refuse is left within the package, 7

i.e., the ruptured vial, it is a batch type operation, and it is not easily adaptable to a production operation.

OBJECTS OF THE INVENTION Accordingly, it is the primary aim of this invention to provide a method of getting sterilized articles within individual bacteria impervious packages so that the articles can be handled and stored within the packages for.

extended periods of time and still remain sterile.

Another object is to provide a method for packing and sterilizing articles which is compatible with highspeed packing line operations.

A more specific object is to provide a method wherein the gaseous sterilant is instantaneously admitted within the packages and the permeability of the packages is relied on to control the sterilant concentration and the gradual dissipation of the sterilant.

BRIEF SUMMARY OF THE INVENTION In accordance with the invention, articles which are to be sterilized and remain sterile until used are packaged individually in bacteria impervious, gas permeable packages. A charge of gaseous sterilant is admitted to each package and the packages are moved to a holding area where the sterilization process is completed and the sterilant concentration within the packages is reduced as the sterilant permeates the packages.

' BRIEF DESCRIPTION OF THE DRAWINGS Other objects and advantages of the invention will within the package after the vacuum is drawn and the fourth side of the package is sealed.

FIG. 4 is a perspective of the package after the sterilant has been admitted with the needle used for injecting the sterilant not yet withdrawn.

While the invention will be described in connection with a preferred procedure, it will be understood that it is not intended to limit the invention to that procedure. On the contrary, it is intended to cover all alternatives, modifications and equivalences as may be included within the spirit and scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION OF THE INVENTION Turning first to FIG. 1 there is shown an article 11 partially enclosed in its own individual package 17. The

package 17 can be formed by superposing two coextensive sheets of gas permeable, bacteria impervious material, bottom sheet and top sheet 16, and bonding these two sheets together along three edges with seal strips 12; leaving a portal large enough so the article 11 to be sterilized can be inserted between the two superposed packaging sheets.

The packaging material is preferably of the thermoplastic, heat sealable type which are gas permeable and bacteria impervious. The permeability constants for any gas (usually expressed in: volume of gas [at standard temperature and pressure] transmitted, per

time period, per area of film transmitting gas, per gas partial pressure differential across the film, per unit of film thickness, i.e., volume/time/film area/pressure differential/film thickness) vary greatly according to the nature of the film materials, the variances being related to the physical and chemical characteristics of the film.

Amorphous polymers have higher permeabilities than crystalline polymers. For example, highly crystalline cellulose has a lower permeability than the less crystalline cellulose acetate.'However, crystallinity alone does not necessarily determine the transmission rate, as is shown by considering the permeation through polyethylene, polytrifluoromonochloroethylene, and

poly (vinylidene chloride), all crystalline polymers, but

with greatly differing permeabilities. Poly (vinylidene chloride) is a symmetrical molecule with a high cohesive energy density and has a very low permeability. Polyethylene is even more symmetrical, but the cohesive energy density is much lower and it has a much larger permeability constant. Polytrifluoromonochloroethylene is unsymmetrical but has a high cohesive energy density and has a permea bility intermediate the other two polymers. Therefore the cohesive energy density of a polymer is very determinant of its permeability.

' In an unsymmetrical molecule such as rubber hydrochloride, the poor symmetry which interferes,

with molecular packing results in a more open structure and consequently higher permeability. A similar effect should result from branching of the polymer 7 chains because branching produces a less regular structure which is not readily incorporated into a space lattice. Therefore there is an inverse correlation between the density and permeability of film, i.e., as the polymer density decreases its permeability increases.

An increase in the degree of cross linking may decrease the rate of permeation owing to the consequent stabilization of segmental motion. Thus, irradiacted polyethylene has been found less permeable than untreated polyethylene. On the other hand, increasing chain flexibility would increase the ease of permeation.

The thermoplastic films are bacteria impervious as long as they are free from any holes. Bacteria are much larger than gas molecules, thus bacteria cannot pass through a solid film, but the slightest hole even a pin hole can be sufficient to permit bacteria to pass through. Therefore, the processing of a film must be analyzed to determine whether pin holes could be in the film, e.g., some films are electrostatically processed to give the film printability and are not acceptable from a bacteria impervious standpoint because the process can cause pin holes in the film.

Low density polyethylene film 0.003 inches thick as is well known to those skilled in the packaging art and commercially available from Ethyl Corporation, Baton Rouge, La. as l-Ii-Slip Shrink Visqueen Film was chosen material. If a non-heat sealing material is used as a packaging material because of its permeability proper- I ties or any other properties, the seal strip 12 between the two sheets of

packaging material

15 and 16 can be formed by adhesives-compatible with the packaging material which are well known to those of ordinary skill in the adhesive art. 7

' The package 17, which acts as the sterilization chamber, must 'have the proper permeability properties, i.e., it must contain the sterilant long enough to effect sterilization within the package but must also release the sterilant at a rate fast enough so the concentration within the package upon shipment is low enough that the danger of physical harm to humans from further permeation is substantially reduced. 5

Sterilization of an article is dependent upon an inverse function between sterilant concentration and time exposed to that sterilant concentration. A packaging materials permeability rate will control the sterilant concentration and the length of time this concentration exists, therefore selection of a packaging material with the proper permeability properties is important when sterilizing within a permeable package. I

There are alternate methods of encapsulating article 11 within package 17, for example, interposing article 11 between two superposed, coextensive, heat sealable sheets, bottom sheet 15 and top sheet 16, before any of the seal strips 12 are made; after this stack-up of bottom sheet 15-article ll-top sheet 16 is made, the seal strips 12 can be made byan appropriate means, e.g.', with a thermal impulse heat sealer which is well known to those skilled in the packaging arts and commercially available from Vertrod, Brooklyn, N.Y. (hereinafter referred to as a Vertrod).

Package 17 of FIG. 1, closed on three sides with a Vertrod and with article 11 inserted, is ready to be completely sealed. When the package is used as the sterilization chamber, it is advantageous to initially expel all air from the package interior, therefore a vacuum is drawn on the package interior before the sterilant is admitted. The packages shown in FIGS. 2 and 3 show that vacuum packing removes all the air possible. The expelled air carries unwanted organisms with it and leaves more free space for the sterilant so the sterilant can be injected without inducing extreme internal pressure on the package. Also, no dilution of the sterilant occurs, and better diffusion and penetration by the sterilant occurs if the air is removed from the package before the sterilant is admitted.

Preferably encapsulation of article 11 is completed by sealing the fourth side of package 17 in a vacuum sealer. It is a machine which draws a vacuum on the package, clamps the open edge of the package, and then heat seals the open edge of the package. One brand of vacuum sealer is the Flex Vac available from the Standard Packing Corporation, New York, N.Y. The vacuum on the package interior can also be drawn after the package is completely sealed, i.e., by puncturing the package, subjecting it to a vacuum, and subsequently rescaling it to maintain the vacuum on the package interior.

Several sterilants and sterilant concentrations are available to choose from. Ethylene oxide is the most preferred sterilant because it is highly effective and generally available, and a mixture consisting essentially of nominally 12 percent ethylene oxide, 44 percent Freon 11, and 44 percent Freon l2, commercially available from The Matheson Company, Inc., East Rutherford, N.J., is a preferred mixture because it is below the flammability threshold of the ethylene oxide. Another sterilant which could be used is propylene oxide. These sterilants are both noxious and dangerous, i.e., at certain concentration levels they become toxic, flammable, and explosive, and for these reasons must be handled cautiously. For example, the maximum allowable exposure concentration of ethylene oxide for humans is 3,000 parts per million (ppm). But ethylene oxide has a built-in warning factor in that at 700 ppm it will irritate ones nose and eyes, thus drawing attention to the fact that a potentially toxic condition exists. The recommended 8 hour exposure level to ethylene oxides is 100 ppm; as a comparison, the level recommended for ammonia is 50 ppm. In concentrations of greater than approximately 30,000 ppm in air it is flammable and if contained, it is explosive. Liquid ethylene oxide boils, i.e., vaporizes, at about 51 F at 1 atmosphere of pressure.

As shown in FIG. 4, the sterilant can be injected through a hollow probe 13, e.g., a number hyperchrome stainless hypodermic needle, with a luerlok fitting as is well known to men of ordinary skill in the injection art and available from Becton, Dickinson & Co., Rutherford, N.J., which pierces the package 17. The needle is attached to a common gas syringe as is well known to those skilled in the art and commercially available from Hamilton Co., Inc. Whittier, California as a Super Syringe, Model No. 8-1500, 1.5 liter; the

syringe is loaded with the desired quantity of the gaseous sterilant; the needle is pushed through one sheet of the package 17 so that the dispensing orifice of the needle is located within the confines of the package 17; and the sterilant is then forced through the needle 13 and into package 17. After the desired quantity of sterilant is put inside package 17, needle 13 is removed from package 17 and a seal tape 14 is used to seal the aperture remaining in the package after needle 13 is removed. The aperture is sealed by covering it with tape 14. FIG. 4 shows package 17 with the sterilant inside and seal tape 14 in position ready to seal the aperture when needle 13 is withdrawn. The seal tape 14 can be any material which will form a bacteria impervious seal. Ordinary cellophane tape such as Scotch brand tape sold by the Minnesota, Mining, & Manufacturing Co., St. Paul, Minn., has been found to perform well as a seal tape 14.

There are other ways to get a sterilizing atmosphere within a sealed package. One alternative to the hypodermic needle is a high pressure nozzle which does not enter the package 17, but delivers the sterilant to the exterior surface of the package at apressure high enough to force the narrow stream of sterilant through one wall of a package 17. Equipment to inject sterilant in this manner would be similar to the pneumatic innoculation equipment used by the U. S. Armed Forces for innoculations whereby the serum is forced through the epidermis of the shot recipient. A liquid sterilant is more easily delivered by means of this system than is a gaseous sterilant, but the high pressure nozzle will deliver either. a liquid or gaseous sterilant. A seal'tape 14 is also preferably used to close the opening made in package 17 when the sterilant is admitted via a high pressure nozzle.

A third way to get a sterilizing atmosphere inside the package 17 is to form, fill, and seal the package within an atmosphere of the sterilant. Sealed package 17 with entrapped sterilant is then moved out of the sterilizing atmosphere to the holding area. This method is particularly well adapted for use with one of the non-explosive sterilizing gas mixtures.

After the sterilant is put inside the package, the package is moved to a holding area where the sterilization of article 11 is completed. Each package 17 acts as a sterilization chamber for its own enclosed article 11 and maintains a sterilizing concentration for a time period sufficient to sterilize article 11 and the interior of package 17. The conditions in this holding area are not critical except that it should be well ventilated. Ventilation is necessary to prevent the build-up of sterilant concentrations greater than the toxic or flammability thresholds for the sterilant used. A complete change of air approximately once every minute is suff cient to keep the sterilant concentration at less than ppm, the maximum continuous exposure level for ethylene oxide, if the ethylene oxide is permeating 3 mil, low density, polyethylene film. Sterilant concentration build-ups are likely to occur if the holding area is not ventilated because the sterilant is heavier than air and thus will tend to settle and fill a room from the bottom to the top. The air taken from the holding area can be processed to remove or render harmless the sterilant therewithin.

The temperature of the holding area can be varied in order to get different sterilization times, but room temperature is usually sufficient to provide satisfactory sterilization times. The preferred temperature range is 70 F and above. With temperatures below 70 F the time required to achieve sterilization can be very long. Higher temperatures yield shorter sterilization times because the higher temperature speeds up the chemical process wherein the bacteria are destroyed.

After a sufficient time period has elapsed for sterilization to be completed for a given sterilant concentration and holding area temperature, e.g., six hours for 9.1 percent ethylene oxide and 73 F, the package 17 can be removed from the holding area and placed in a normal storage area. One factor to consider in removing the sterilized packages from the holding area is whether the sterilant remaining within package 17 will, after permeating the package, accumulate in concentrations which surpass the toxic or flammability thresholds. To be completely safe, the package 17 should preferably be held in the ventilated holding area until substantially all the sterilant has permeated the package; then little sterilant would remain to accumulate in concentrations greater than the danger thresholds.

EXAMPLE I An absorbent pad constructed in accordance with the teachings of U. S. Pat. Re. 26,151, Disposable Diaper, Reissued Jan. 31, 1967 without the plastic backsheet, weighing 55.12 grams and measuring 11.0 X 21.0 X 1.6 centimetersin a folded condition and a Bacterial Spore Strip, such as the Spordex made by American Sterilizer Company of Erie, Penna, were inserted between two superposed sheets of the 3 mil, low density, polyethylene film, mentioned above, which previously were heat sealed together along three sides of the prospective package with a Vertrod heat sealer mentioned above. The partially closed package was then placed in the Flex Vac, mentioned above, wherein a vacuum of approximately 29 inches of mercury was drawn on the package interior and the fourth side of the package was heat sealed. The package was then removed from the Flex Vac and the fourth side was resealed on the Vertrod to insure that the fourth side was sealed tightly. The dimensions of the package within the seal strips were 12.7 X 23.0 X 1.0 centimeters, yielding a package surface area of approximately 584.2 square centimeters. 400 cubic centimeters, of the nominal 12 percent ethylene oxide mentioned above was loaded at room temperature (70-7 5 F) and atmospheric pressure into the gas syringe mentioned above from a pressurized tank of the sterilant. A number hypodermic needle was then attached to the gas syringe and the needle was forced through one package wall and into the disposable diaper. The gaseous sterilant mixture was then injected into the package, the needle was withdrawn from the package,

' and a seal tape of the cellophane tape mentioned above was placed over the aperture left by the needle. The package was then immediately moved to a 73 F, constant temperature room, where it was stored on an open, imperforate shelf with nothing placed on top of it. The package was withdrawn after six hours and the spore strip was removed using sterile techniques and EXAMPLE II A package was prepared encapsulating an absorbent pad, spore strip and sterilant as described in EXAM- PLE l, was placed in a F, constant temperature room, and was removed after 2 hours in the 120 F holding area. The spore strip, removed and processed as described in EXAMPLE 1, indicated no living organisms remained in the package. Exposure to the sterilant for 2 hours at 120 F was sufficient to eliminate all bacteria in the package when the sterilant charge was 400 milliliters of ethylene oxide even ,though the sterilant was constantly escaping by permeation.

EXAMPLE III A package was prepared from the 1.5 mil polypropylene film mentioned above, encapsulating an absorbent pad and spore strip, and 500 milliliters of ethylene oxide was injected, all as described in EXAM- PLE I. The package then was placed in a 120 F, constant temperature room and was removed after 2 hours in the 120 F holding area. The spore strip, removed and processed as described in EXAMPLE 1, indicated no living organisms remained in the package. Exposure to the sterilant for 2 hours at 120 F was sufficient to eliminate all bacteria in the package when the sterilant charge was 500 milliliters of ethylene oxide even though the sterilant was constantly escaping by permeation.

Thus it is apparent that there has been provided, in accordance with the invention, a method of in package sterilization that fully satisfies the objects, aims and advantages set forth above. While the invention has been described in conjunction with specific embodiments thereof it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and broad scope of the appended claims.

We claim:

1. The method of manufacturing sterilized articles comprising: sequentially a. encapsulating one or more articles within a gaspermeable, bacteria-impervious package;

b. impinging a high pressure stream of sterilant upon said package to create an aperture in the package wall, whereby said sterilant is forced through the wall of the package and the sterilant immediately contacts said one or more articles within the package;

. placing the sterilant-containing package in a wellventilated holding area; and

. holding said package in said holding area while a substantial portion of the sterilant permeates the package, whereby upon shipment, danger of physical harm to humans from further permeation of the sterilant is substantially reduced.

Claims

1. The method of manufacturing sterilized articles comprising: sequentially a. encapsulating one or more articles within a gas-permeable, bacteria-impervious package; b. impinging a high pressure stream of sterilant upon said package to create an aperture in the package wall, whereby said sterilant is forced through the wall of the package and the sterilant immediately contacts said one or more articles within the package; c. placing the sterilant-containing package in a well-ventilated holding area; and d. holding said package in said holding area while a substantial portion of the sterilant permeates the package, whereby upon shipment, danger of physical harm to humans from further permeation of the sterilant is substantially reduced.